Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

We present a concept of a millimeter wavefront sensor that allows real-time sensing of the surface of a groundbased millimeter/submillimeter telescope. It is becoming important for ground-based millimeter/submillimeter astronomy to make telescopes larger with keeping their surface accurate. To establish 'millimetric adaptive optics (MAO)' that instantaneously corrects the wavefront degradation induced by deformation of telescope optics, our wavefront sensor based on radio interferometry measures changes in excess path lengths from characteristic positions on the primary mirror surface to the focal plane. This plays a fundamental role in planed 50-m class submillimeter telescopes such as LST and AtLAST.

DOI： 10.1117/12.2561885

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

Ultra-wideband 3D imaging spectrometry in the millimeter-submillimeter
(mm-submm) band is an essential tool for uncovering the dust-enshrouded portion
of the cosmic history of star formation and galaxy evolution. However, it is
challenging to scale up conventional coherent heterodyne receivers or
free-space diffraction techniques to sufficient bandwidths ($\geq$1 octave) and
numbers of spatial pixels (>$10^2$). Here we present the design and first
astronomical spectra of an intrinsically scalable, integrated superconducting
spectrometer, which covers 332-377 GHz with a spectral resolution of $F/\Delta
F \sim 380$. It combines the multiplexing advantage of microwave kinetic
inductance detectors (MKIDs) with planar superconducting filters for dispersing
the signal in a single, small superconducting integrated circuit. We
demonstrate the two key applications for an instrument of this type: as an
efficient redshift machine, and as a fast multi-line spectral mapper of
extended areas. The line detection sensitivity is in excellent agreement with
the instrument design and laboratory performance, reaching the atmospheric
foreground photon noise limit on sky. The design can be scaled to bandwidths in
excess of an octave, spectral resolution up to a few thousand and frequencies
up to $\sim$1.1 THz. The miniature chip footprint of a few $\mathrm{cm^2}$
allows for compact multi-pixel spectral imagers, which would enable
spectroscopic direct imaging and large volume spectroscopic surveys that are
several orders of magnitude faster than what is currently possible.

DOI： 10.1038/s41550-019-0850-8

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Cosmological simulations predict that the Universe contains a network of intergalactic gas filaments, within which galaxies form and evolve. However, the faintness of any emission from these filaments has limited tests of this prediction. We report the detection of rest-frame ultraviolet Lyman-α radiation from multiple filaments extending more than one megaparsec between galaxies within the SSA22 protocluster at a redshift of 3.1. Intense star formation and supermassive black-hole activity is occurring within the galaxies embedded in these structures, which are the likely sources of the elevated ionizing radiation powering the observed Lyman-α emission. Our observations map the gas in filamentary structures of the type thought to fuel the growth of galaxies and black holes in massive protoclusters....

DOI： 10.1126/science.aaw5949

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

<title>Abstract</title>
We present new ALMA observations and physical properties of a Lyman break galaxy at z = 7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, MUV ≈ −22.4, and has been spectroscopically identified in Lyα with a small rest-frame equivalent width of ≈4 Å. A previous Hubble Space TElescope (HST) image has shown that the target is composed of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [O iii] 88 μm, [C ii] 158 μm, and their underlying dust continuum emission. In the whole system of B14-65666, the [O iii] and [C ii] lines have consistent redshifts of 7.1520 ± 0.0003, and the [O iii] luminosity, (34.4 ± 4.1) × 108 L⊙, is about three times higher than the [C ii] luminosity, (11.0 ± 1.4) × 108 L⊙. With our two continuum flux densities, the dust temperature is constrained to be Td ≈ 50–60 K under the assumption of a dust emissivity index of βd = 2.0–1.5, leading to a large total infrared luminosity of LTIR ≈ 1 × 1012 L⊙. Owing to our high spatial resolution data, we show that the [O iii] and [C ii] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by ≈200 km s−1. We also find these two clumps have comparable UV, infrared, [O iii], and [C ii] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major merger. The merger interpretation is also supported by the large specific star formation rate (defined as the star formation rate per unit stellar mass), sSFR $= 260^{+119}_{-57}\:$Gyr−1, inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [O iii]-to-[C ii] luminosity ratio.

DOI： 10.1093/pasj/psz049

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Language：Japanese   Publishing type：Research paper (scientific journal)  

A fundamental quest of modern astronomy is to locate the earliest galaxies and study how they influenced the intergalactic medium a few hundred million years after the Big Bang<SUP>1-3</SUP>. The abundance of star-forming galaxies is known to decline<SUP>4,5</SUP> from redshifts of about 6 to 10, but a key question is the extent of star formation at even earlier times, corresponding to the period when the first galaxies might have emerged. Here we report spectroscopic observations of MACS1149-JD1<SUP>6</SUP>, a gravitationally lensed galaxy observed when the Universe was less than four per cent of its present age. We detect an emission line of doubly ionized oxygen at a redshift of 9.1096 ± 0.0006, with an uncertainty of one standard deviation. This precisely determined redshift indicates that the red rest-frame optical colour arises from a dominant stellar component that formed about 250 million years after the Big Bang, corresponding to a redshift of about 15. Our results indicate that it may be possible to detect such early episodes of star formation in similar galaxies with future telescopes....

DOI： 10.1038/s41586-018-0117-z

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For efficient spectroscopic redshift identification of early galaxies in the northern hemisphere, we aim to combine the Large Millimeter Telescope (LMT) with a wide-band heterodyne receiver, FINER, which will cover radio frequencies of 120-360 GHz and offer a 3-21 GHz intermediate frequency (IF) per sideband and polarization. To take full advantage of such wide IFs, we present a novel 10.24-GHz-wide digital spectrometer, DRS4 (Elecs Industry Co., Ltd.). It incorporates 20.48 Gsps samplers with an FPGA-based digital signal processing module. To mitigate the noise contamination from the image sideband, it is equipped with a digital sideband separation function to improve the sideband rejection up to 25 dB. Laboratory performance evaluations show that it exhibits an Allan time of at least ∼ 100 s and a total power dynamic range of at least 7 dB. These results demonstrate its capability of instantaneously wide-band spectroscopy toward high-redshift galaxies with position-switching observations.

DOI： 10.1117/12.3018296

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Spectroscopic observations of the far-infrared [O iii] 88 µm and [C ii] 158 µm lines present a pathway to explore the mechanisms of the emergence of massive galaxies in the epoch of reionization and beyond, which is one of the most fundamental questions in astronomy. To address this question, the Far-Infrared Nebular Emission Receiver (FINER) project is developing two wideband dual-polarization sideband-separating heterodyne receivers at 120-210 GHz and 210-360 GHz for the Large Millimeter Telescope (LMT) in Mexico. Compared with Atacama Large Millimeter/submillimeter Array (ALMA), LMT provides 40% of ALMA's light-collecting area and a similar atmospheric transmittance, but FINER plans to have an instantaneous intermediate frequency (IF) of 3-21 GHz per sideband per polarization which is five times wider than current ALMA's bandwidth. Therefore, FINER is going to offer cutting-edge spectral scanning capability in the next several years. The project is currently in an active development phase. In this proceeding, the latest development status for FINER, including the optics, wideband waveguide components as well as low-noise superconductor-insulator-superconductor (SIS) mixers is reported.

DOI： 10.1117/12.3018190

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We present Atacama Large Millimetre/submillimetre Array (ALMA) observations of the [O iii] 88 emission of a sample of thirteen galaxies at to 7.6 selected as [C ii]-emitting companion sources of quasars. To disentangle the origins of the luminous Oxygen line in the Universe, we looked at emission-line galaxies that are selected through an excellent star-formation tracer [C ii] with star-formation rates between 9 and 162. Direct observations reveal [O iii] emission in just a single galaxy (), and a stacked image shows no [O iii] detection, providing deep upper limits on the ratios in the Universe (at). While the fidelity of this sample is high, no obvious optical/near-infrared counterpart is seen in the JWST imaging available for four galaxies. Additionally accounting for low-z CO emitters, line stacking shows that our sample-wide result remains robust: The enhanced reported in the first billion years of the Universe is likely due to the selection towards bright, blue Lyman-break galaxies with high surface star-formation rates or young stellar populations. The deep upper limit on the rest-frame 90 μm continuum emission (Jy at), implies a low average dust temperature (K) and high-dust mass (). As more normal galaxies are explored in the early Universe, synergy between JWST and ALMA is fundamental to further investigate the ISM properties of the a broad range of samples of high-z galaxies.

DOI： 10.1093/mnras/stae1613

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We report on deep SCUBA-2 observations at 850 μm and NOrthern Extended Millimetre Array (NOEMA) spectroscopic measurements at 2 mm of the environment surrounding the luminous, massive (M∗ ≈ 2 × 1011 M☉) Herschel-selected source HerBS-70. This source was revealed by previous NOEMA observations to be a binary system of dusty star-forming galaxies at z = 2.3, with the east component (HerBS-70E) hosting an active galactic nucleus. The SCUBA-2 observations detected, in addition to the binary system, 21 sources at >3.5σ over an area of ∼25 square comoving Mpc with a sensitivity of 1σ850 = 0.75 mJy. The surface density of continuum sources around HerBS-70 is three times higher than for field galaxies. The NOEMA spectroscopic measurements confirm the protocluster membership of three of the nine brightest sources through their CO(4–3) line emission, yielding a volume density 36 times higher than for field galaxies. All five confirmed sub-mm galaxies in the HerBS-70 system have relatively short gas depletion times (80−500 Myr), indicating the onset of quenching for this protocluster core due to the depletion of gas. The dark matter halo mass of the HerBS-70 system is estimated around 5 × 1013 M☉, with a projected current-day mass of 1015 M☉, similar to the local Virgo and Coma clusters. These observations support the claim that DSFGs, in particular the ones with observed multiplicity, can trace cosmic overdensities.

DOI： 10.1093/mnras/stae1155

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We present Atacama Large Millimeter/submillimeter Array (ALMA) deep spectroscopy for a lensed galaxy at z spec = 8.496 with log ( M star / M ⊙ ) ∼ 7.8 whose optical nebular lines and stellar continuum are detected by JWST/NIRSpec and NIRCam Early Release Observations in the field of SMACS J0723.3-7327. Our ALMA spectrum shows [O iii] 88 μm and [C ii] 158 μm line detections at 4.0σ and 4.5σ, respectively. The redshift and position of the [O iii] line coincide with those of the JWST source, while the [C ii] line is blueshifted by 90 km s−1 with a spatial offset of 0.″5 (≈0.5 kpc in the source plane) from the centroid of the JWST source. The NIRCam F444W image, including [O iii] λ5007 and Hβ line emission, spatially extends beyond the stellar components by a factor of >8. This indicates that the z = 8.5 galaxy has already experienced strong outflows as traced by extended [O iii] λ5007 and offset [C ii] emission, which would promote ionizing photon escape and facilitate reionization. With careful slit-loss corrections and the removal of emission spatially outside the galaxy, we evaluate the [O iii] 88 μm/λ5007 line ratio, and derive the electron density n e by photoionization modeling to be 220 − 130 + 230 cm−3, which is comparable with those of z ∼ 2-3 galaxies. We estimate an [O iii] 88 μm/[C ii] 158 μm line ratio in the galaxy of >4, as high as those of known z ∼ 6-9 galaxies. This high [O iii] 88 μm/[C ii] 158 μm line ratio is generally explained by the high n e as well as the low metallicity ( Z gas / Z ⊙ = 0.04 − 0.02 + 0.02 ), high ionization parameter ( log U > − 2.27 ), and low carbon-to-oxygen abundance ratio (log(C/O) = [−0.52: −0.24]) obtained from the JWST/NIRSpec data; further [C ii] follow-up observations will constrain the covering fraction of photodissociation regions.

DOI： 10.3847/1538-4357/ad235c

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

Abstract

We present emission maps ($1\buildrel{\,\prime}\over{.} 5\,\times \,1\buildrel{\,\prime}\over{.} 5$ scale, corresponding to 0.18 pc) of the DCN (J = 2 − 1) and DCO⁺ (J = 2 − 1) lines in the 2 mm band toward the Orion KL region obtained with the 2 mm receiver system named B4R installed on the Large Millimeter Telescope. The DCN emission shows a peak at the Orion KL hot core position, whereas no DCO⁺ emission has been detected there. The DCO⁺ emission shows enhancement at the west side of the hot core, which is well shielded from the UV radiation from OB massive stars in the Trapezium cluster. We have derived the abundance ratio of DCN/DCO⁺ at three representative positions where both species have been detected. The gas components with V_LSR ≈ 7.5–8.7 km s⁻¹ are associated with low abundance ratios of ∼4–6, whereas much higher abundance ratios (∼22–30) are derived for the gas components with V_LSR ≈ 9.2–11.6 km s⁻¹. We have compared the observed abundance ratio to our chemical models and found that the observed differences in the DCN/DCO⁺ abundance ratios are explained by different densities.

DOI： 10.3847/1538-4357/ad1e5a

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DOI： 10.3847/1538-4357/ad0df5

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We present results of [C II] 158 μm emission line observations, and report the spectroscopic redshift confirmation of a strongly lensed (μ ∼ 20) star-forming galaxy, MACS0308-zD1 at z = 6.2078 ± 0.0002. The [C II] emission line is detected with a signal-to-noise ratio >6 within the rest-frame UV-bright clump of the lensed galaxy (zD1.1) and exhibits multiple velocity components; the narrow [C II] has a velocity full width half maximum (FWHM) of 110 ± 20 km s−1, while broader [C II] is seen with an FWHM of 230 ± 50 km s−1. The broader [C II] component is blueshifted (−80 ± 20 km s−1) with respect to the narrow [C II] component, and has a morphology that extends beyond the UV-bright clump. We find that, while the narrow [C II] emission is most likely associated with zD1.1, the broader component is possibly associated with a physically distinct gas component from zD1.1 (e.g., outflowing or inflowing gas). Based on the nondetection of λ158μm dust continuum, we find that MACS0308-zDl's star formation activity occurs in a dust-free environment indicated by a strong upper limit of infrared luminosity ≲9 × 108 Le. Targeting this strongly lensed faint galaxy for follow-up Atacama Large Millimeter/submillimeter Array and JWST observations will be crucial to characterize the details of typical galaxy growth in the early Universe.

DOI： 10.3847/1538-4357/ad0f95

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DOI： 10.3847/2041-8213/acff63

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We present an imaging molecular line survey in the 3 mm band (85–114 GHz) focused on one of the nearest galaxies with an active galactic nucleus (AGN), NGC 1068, based on observations taken with the Atacama Large Millimeter/submillimeter Array. Distributions of 23 molecular transitions are obtained in the central ∼3 kpc region, including both the circumnuclear disk (CND) and starburst ring (SBR) with 60 and 350 pc resolution. The column densities and relative abundances of all the detected molecules are estimated under the assumption of local thermodynamic equilibrium in the CND and SBR. Then, we discuss the physical and chemical effects of the AGN on molecular abundance corresponding to the observation scale. We found that H¹³CN, SiO, HCN, and H¹³CO⁺ are abundant in the CND relative to the SBR. In contrast, ¹³CO is more abundant in the SBR. Based on the calculated column density ratios of N(HCN)/N(HCO⁺), N(HCN)/N(CN), and other molecular distributions, we conclude that the enhancement of HCN in the CND may be due to high-temperature environments resulting from strong shocks, which are traced by the SiO emission. Moreover, the abundance of CN in the CND is significantly lower than the expected value of the model calculations in the region affected by strong radiation. The expected strong X-ray irradiation from the AGN has a relatively lower impact on the molecular abundance in the CND than mechanical feedback.

DOI： 10.3847/1538-4357/ace4c7

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We report the physical characterization of four CO emitters detected near the bright submillimeter galaxy (SMG) SSA22-AzTEC26. We analyze the data from Atacama Large Millimeter/submillimeter Array band 3, 4, and 7 observations of the SSA22-AzTEC26 field. In addition to the targeted SMG, we detect four line emitters with signal-to-noise ratio >5.2 in the cube smoothed with a 300 km s−1 FWHM Gaussian filter. All four sources have NIR counterparts within 1″. We perform UV-to-FIR spectral energy distribution modeling to derive the photometric redshifts and physical properties. Based on the photometric redshifts, we reveal that two of them are CO(2-1) at redshifts of 1.113 and 1.146 and one is CO(3-2) at z = 2.124. The three sources are massive galaxies with a stellar mass ≳1010.5 M ⊙, but have different levels of star formation. Two lie within the scatter of the main sequence (MS) of star-forming galaxies at z ∼ 1-2, and the most massive galaxy lies significantly below the MS. However, all three sources have a gas fraction within the scatter of the MS scaling relation. This shows that a blind CO line search can detect massive galaxies with low specific star formation rates that still host large gas reservoirs and that it also complements targeted surveys, suggesting later gas acquisition and the need for other mechanisms in addition to gas consumption to suppress star formation.

DOI： 10.3847/1538-4357/ace0c0

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We report Atacama Large Millimeter/submillimeter Array Band 3 observations of CO(6−5), CO(7−6), and [C i](2−1) in B14-65666 (“Big Three Dragons”), one of the brightest Lyman-break galaxies at z > 7 in the rest-frame ultraviolet continuum, far-infrared continuum, and emission lines of [O iii] 88 μm and [C ii] 158 μm. CO(6−5), CO(7−6), and [C i](2−1), whose 3σ upper limits on the luminosities are approximately 40 times fainter than the [C ii] luminosity, are all not detected. The L [C II]/L CO(6-5) and L [C II]/L CO(7-6) ratios are higher than the typical ratios obtained in dusty star-forming galaxies or quasar host galaxies at similar redshifts, and they may suggest a lower gas density in the photodissociated region in B14-65666. By using the (1) [C ii] luminosity, (2) dust mass-to-gas mass ratio, and (3) a dynamical mass estimate, we find that the molecular gas mass (M mol) is (0.05-11) × 1010 M ⊙. This value is consistent with the upper limit inferred from the nondetection of mid-J CO and [C i](2−1). Despite the large uncertainty in M mol, we estimate a molecular gas-to-stellar mass ratio (μ gas) of 0.65-140 and a gas depletion time (τ dep) of 2.5-550 Myr; these values are broadly consistent with those of other high-redshift galaxies. B14-65666 could be an ancestor of a passive galaxy at z ≳ 4 if no gas is fueled from outside the galaxy.

DOI： 10.3847/1538-4357/acdd5c

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We present integral field, far-infrared (FIR) spectroscopy of Mrk 54, a local Lyman continuum emitter, obtained with FIFI-LS on the Stratospheric Observatory for Infrared Astronomy. This is only the second time, after Haro 11, that [C ii] 158 mu m and [O iii] 88 mu m spectroscopy of the known LCEs have been obtained. We find that Mrk 54 has a strong [C ii] emission that accounts for similar to 1% of the total FIR luminosity, whereas it has only moderate [O iii] emission, resulting in the low [O iii]/[C ii] luminosity ratio of 0.22 +/- 0.06. In order to investigate whether [O iii]/[C ii] is a useful tracer of f (esc) (LyC escape fraction), we examine the correlations of [O iii]/[C ii] and (i) the optical line ratio of O-32 equivalent to [O iii] 5007 angstrom/[O ii] 3727 angstrom, (ii) specific star formation rate, (iii) [O iii] 88 mu m/[O i] 63 mu m ratio, (iv) gas-phase metallicity, and (v) dust temperature based on a combined sample of Mrk 54 and the literature data from the Herschel Dwarf Galaxy Survey and the LITTLE THINGS Survey. We find that galaxies with high [O iii]/[C ii] luminosity ratios could be the result of high ionization (traced by O-32), bursty star formation, high ionized-to-neutral gas volume filling factors (traced by [O iii] 88 mu m/[O i] 63 mu m), and low gas-phase metallicities, which is in agreement with theoretical predictions. We present an empirical relation between the [O iii]/[C ii] ratio and f (esc) based on the combination of the [O iii]/[C ii] and O-32 correlation, and the known relation between O-32 and f (esc). The relation implies that high-redshift galaxies with high [O iii]/[C ii] ratios revealed by the Atacama Large Millimeter/submillimeter Array may have f (esc) greater than or similar to 0.1, significantly contributing to the cosmic reionization.

DOI： 10.3847/1538-4357/acc530

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DOI： 10.3847/1538-3881/acb707

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Monthly Notices of the Royal Astronomical Society  

We present 101- and 151-GHz ALMA continuum images for 85 fields selected from Herschel observations that have 500-μm flux densities >80 mJy and 250–500-μm colours consistent with z > 2, most of which are expected to be gravitationally lensed or hyperluminous infrared galaxies. Approximately half of the Herschel 500-μm sources were resolved into multiple ALMA sources, but 11 of the 15 brightest 500-μm Herschel sources correspond to individual ALMA sources. For the 37 fields containing either a single source with a spectroscopic redshift or two sources with the same spectroscopic redshift, we examined the colour temperatures and dust emissivity indices. The colour temperatures only vary weakly with redshift and are statistically consistent with no redshift-dependent temperature variations, which generally corresponds to results from other samples selected in far-infrared, submillimetre, or millimetre bands but not to results from samples selected in optical or near-infrared bands. The dust emissivity indices, with very few exceptions, are largely consistent with a value of 2. We also compared spectroscopic redshifts to photometric redshifts based on spectral energy distribution templates designed for infrared-bright high-redshift galaxies. While the templates systematically underestimate the redshifts by ∼15 per cent, the inclusion of ALMA data decreases the scatter in the predicted redshifts by a factor of ∼2, illustrating the potential usefulness of these millimetre data for estimating photometric redshifts.

DOI： 10.1093/mnras/stac3771

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Monthly Notices of the Royal Astronomical Society  

We analyse the molecular and atomic emission lines of 71 bright Herschel-selected galaxies between redshifts 1.4 and 4.6 detected by the Atacama Large Millimeter/submillimeter Array. These lines include a total of 156 CO, [C i], and H2O emission lines. For 46 galaxies, we detect two transitions of CO lines, and for these galaxies we find gas properties similar to those of other dusty star-forming galaxy (DSFG) samples. A comparison to photodissociation models suggests that most of Herschel-selected galaxies have similar interstellar medium conditions as local infrared-luminous galaxies and high-redshift DSFGs, although with denser gas and more intense far-ultraviolet radiation fields than normal star-forming galaxies. The line luminosities agree with the luminosity scaling relations across five orders of magnitude, although the star formation and gas surface density distributions (i.e. Schmidt-Kennicutt relation) suggest a different star formation phase in our galaxies (and other DSFGs) compared to local and low-redshift gas-rich, normal star-forming systems. The gas-to-dust ratios of these galaxies are similar to Milky Way values, with no apparent redshift evolution. Four of 46 sources appear to have CO line ratios in excess of the expected maximum (thermalized) profile, suggesting a rare phase in the evolution of DSFGs. Finally, we create a deep stacked spectrum over a wide rest-frame frequency (220-890 GHz) that reveals faint transitions from HCN and CH, in line with previous stacking experiments.

DOI： 10.1093/mnras/stad784

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DOI： 10.3847/1538-4357/acb8ab

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DOI： 10.48550/arXiv.2303.04830

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DOI： 10.1093/mnras/stad307

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DOI： 10.1093/mnras/stac3723

DOI： 10.48550/arXiv.2208.13642

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：2023 35th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2023  

In this paper, we present a new data scientific approach for efficient and automated spectroscopy with millimeter and submillimeter single-dish telescopes. The proposed approach avoids direct subtraction between two noisy spectra (i.e. on-source and off-source spectra) that is common in the current data reduction: It then offers us to improve the observation sensitivity by a factor of 2 and reduce artificial baseline ripples in parallel with developing observational instruments. We demonstrate such upgrades in the real observed spectra taken by existing large millimeter single-dish telescopes. We finally discuss the application of the proposed approach for the future large submillimeter single-dish telescopes that will yield petabytes of data resulting from sensitive, wide field (1°2), and wide band (>100 GHz) imaging spectroscopy.

DOI： 10.23919/URSIGASS57860.2023.10265475

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Abstract

We present our new Atacama Large Millimeter/submillimeter Array (ALMA) observations targeting CO(6–5) emission from three luminous Lyman-break galaxies (LBGs) at z_spec = 6.0293–6.2037 found in the Subaru/Hyper Suprime-Cam survey, whose [O iii] 88 μm and [C ii] 158 μm emissions have been detected with ALMA. We find a marginal detection of the CO(6–5) line from one of our LBGs, J0235–0532, at the ≃4σ significance level and obtain upper limits for the other two LBGs, J1211–0118 and J0217–0208. Our z = 6 luminous LBGs are consistent with the previously found correlation between the CO luminosity and the infrared luminosity. The unique ensemble of the multiple far-infrared emission lines and underlying continuum fed to a photodissociation region model reveals that J0235–0532 has a relatively high density of hydrogen nuclei n_H that is comparable to those of low-z (U)LIRGs, quasars, and Galactic star-forming regions with high n_H values, while the other two LBGs have lower n_H consistent with local star-forming galaxies. By carefully taking account of various uncertainties, we obtain constraints on total gas mass and gas surface density from their CO luminosity measurements. We find that J0235–0532 is located below the Kennicutt–Schmidt (KS) relation, comparable to the z = 5.7 LBG, HZ10, previously detected with CO(2–1). Combined with previous results for dusty starbursts at similar redshifts, the KS relation at z = 5–6 is on average consistent with the local one.

DOI： 10.3847/1538-4357/ac9ea6

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DOI： 10.1093/pasj/psac082

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We present a feasibility study for the high-redshift galaxy part of the Science Verification Campaign with the 220–440 GHz deshima 2.0 integrated superconducting spectrometer on the ASTE telescope. The first version of the deshima 2.0 chip has been recently manufactured and tested in the lab. Based on these realistic performance measurements, we evaluate potential target samples and prospects for detecting the [CII] and CO emission lines. The planned observations comprise two distinct, but complementary objectives: (1) acquiring spectroscopic redshifts for dusty galaxies selected in far-infrared/mm-wave surveys; (2) multi-line observations to infer physical conditions in dusty galaxies.

DOI： 10.1007/s10909-022-02730-y

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Integrated superconducting spectrometer (ISS) technology will enable ultra-wideband, integral-field spectroscopy for (sub)millimeter-wave astronomy, in particular, for uncovering the dust-obscured cosmic star formation and galaxy evolution over cosmic time. Here, we present the development of DESHIMA 2.0, an ISS for ultra-wideband spectroscopy toward high-redshift galaxies. DESHIMA 2.0 is designed to observe the 220–440 GHz band in a single shot, corresponding to a redshift range of z = 3.3–7.6 for the ionized carbon emission ([C II] 158 μ m). The first-light experiment of DESHIMA 1.0, using the 332–377 GHz band, has shown an excellent agreement among the on-sky measurements, the laboratory measurements, and the design. As a successor to DESHIMA 1.0, we plan the commissioning and the scientific observation campaign of DESHIMA 2.0 on the ASTE 10-m telescope in 2023. Ongoing upgrades for the full octave-bandwidth system include the wideband 347-channel chip design and the wideband quasi-optical system. For efficient measurements, we also develop the observation strategy using the mechanical fast sky-position chopper and the sky-noise removal technique based on a novel data-scientific approach. In the paper, we show the recent status of the upgrades and the plans for the scientific observation campaign.

DOI： 10.1007/s10909-022-02888-5

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Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

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We report the detection of an ionized gas outflow from an X-ray active galactic nucleus hosted in a massive quiescent galaxy in a protocluster at z = 3.09 (J221737.29+001823.4). It is a type-2 QSO with broad (W₈₀ &gt; 1000 km s⁻¹) and strong ($\mathrm{log}({L}_{[\mathrm{OIII}]}$/erg s⁻¹) ≈ 43.4) [O iii]λλ 4959,5007 emission lines detected by slit spectroscopy in three-position angles using Multi-Object Infra-Red Camera and Spectrograph (MOIRCS) on the Subaru telescope and the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) on the Keck-I telescope. In the all slit directions, [O iii] emission is extended to ∼15 physical kpc and indicates a powerful outflow spreading over the host galaxy. The inferred ionized gas mass outflow rate is 22 ± 3 M_⊙ yr⁻¹. Although it is a radio source, according to the line diagnostics using Hβ, [O ii], and [O iii], photoionization by the central QSO is likely the dominant ionization mechanism rather than shocks caused by radio jets. On the other hand, the spectral energy distribution of the host galaxy is well characterized as a quiescent galaxy that has shut down star formation several hundred Myr ago. Our results suggest a scenario that QSOs are powered after the shutdown of the star formation and help complete the quenching of massive quiescent galaxies at high redshift.

DOI： 10.3847/1538-4357/ac7f2d

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We present spatially resolved morphological properties of [C II] 158 μm, [O III] 88 μm, dust, and rest-frame ultraviolet (UV) continuum emission for A1689-zD1, a strongly lensed, sub-L* galaxy at z = 7.13, by utilizing deep Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope (HST) observations. While the [O III] line and UV continuum are compact, the [C II] line is extended up to a radius of r ∼ 12 kpc. Using multi-band rest-frame far-infrared continuum data ranging from 52 to 400 μm, we find an average dust temperature and emissivity index of T dust = 41 − 14 + 17 K and β = 1.7 − 0.7 + 1.1 , respectively, across the galaxy. We find slight differences in the dust continuum profiles at different wavelengths, which may indicate that the dust temperature decreases with distance. We map the star formation rate (SFR) via IR and UV luminosities and determine a total SFR of 37 ± 1M ⊙yr−1 with an obscured fraction of 87%. While the [O III] line is a good tracer of the SFR, the [C II] line shows deviation from the local L [C II]-SFR relations in the outskirts of the galaxy. Finally, we observe a clear difference in the line profile between [C II] and [O III], with significant residuals (∼5σ) in the [O III] line spectrum after subtracting a single Gaussian model. This suggests a possible origin of the extended [C II] structure from the cooling of hot ionized outflows. The extended [C II] and high-velocity [O III] emission may both contribute in part to the high L [O III]/L [C II] ratios recently reported in z > 6 galaxies.

DOI： 10.3847/1538-4357/ac795b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

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We present new Atacama Large Millimeter/submillimeter Array (ALMA) results obtained from spatially resolved CO J = 2–1 line (0.″4 resolution) and 870 μm continuum (0.″2 resolution) observations of cluster galaxies in XMMXCS J2215.9-1738 at z = 1.46. Our sample comprises 17 galaxies within ∼0.5 Mpc (0.6R₂₀₀) of the cluster center, all of which have previously been detected in the CO J = 2–1 line at a lower resolution. The effective radii of both the CO J = 2–1 line and 870 μm dust continuum emissions are robustly measured for nine galaxies by modeling the visibilities. We find that the CO J = 2–1 line emission in all of the nine galaxies is more extended than the dust continuum emission by a factor of 2.8 ± 1.4. We investigate the spatially resolved Kennicutt–Schmidt (KS) relation in two regions within the interstellar medium of the galaxies. The relation for our sample reveals that the central region (0 &lt; r &lt; R_e,870μm) of galaxies tends to have a shorter gas depletion timescale, i.e., a higher star formation efficiency, compared to the extended region (R_e,870μm &lt; r &lt; R_e,CO). Overall, our result suggests that star formation activities are concentrated inside the extended gas reservoir, possibly resulting in the formation of a bulge structure. We find consistency between the ALMA 870 μm radii of star-forming members and the Hubble Space Telescope/1.6 μm radii of passive members in a mass–size distribution, which suggests a transition from star-forming to passive members within ∼0.5 Gyr. In addition, no clear differences in the KS relation nor in the sizes are found between galaxies with and without a close companion.

DOI： 10.3847/1538-4357/ac6cdc

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DOI： 10.3847/2041-8213/ac7447

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

Abstract

We present observations of [N ii] 205 μm, [O iii] 88 μm, and dust emission in a strongly-lensed, submillimeter galaxy (SMG) at z = 6.0, G09.83808, with the Atacama Large Millimeter/submillimeter Array (ALMA). Both [N ii] and [O iii] line emissions are detected at &amp;gt;12σ in the ${0{^{\prime \prime}_{. } }8}$-resolution maps. Lens modeling indicates that the spatial distribution of the dust continuum emission is well characterized by a compact disk with an effective radius of 0.64 ± 0.02 kpc and a high infrared surface brightness of ΣIR = (1.8 ± 0.3) × 1012 L⊙ kpc−2. This result supports that G09.83808 is the progenitor of compact quiescent galaxies at z ∼ 4, where the majority of its stars are expected to be formed through a strong and short burst of star formation. G09.83808 and other lensed SMGs show a decreasing trend in the [N ii] line to infrared luminosity ratio with increasing continuum flux density ratio between 63 and 158 μm, as seen in local luminous infrared galaxies (LIRGs). The decreasing trend can be reproduced by photoionization models with increasing ionization parameters. Furthermore, by combining the [N ii]/[O iii] luminosity ratio with far-infrared continuum flux density ratio in G09.83808, we infer that the gas phase metallicity is already Z ≈ 0.5–0.7 Z⊙. G09.83808 is likely one of the earliest galaxies that has been chemically enriched at the end of reionization.

DOI： 10.1093/pasj/psac018

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Monthly Notices of the Royal Astronomical Society  

We present spectroscopic measurements for 71 galaxies associated with 62 of the brightest high-redshift submillimetre sources from the Southern fields of the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS), while targeting 85 sources which resolved into 142. We have obtained robust redshift measurements for all sources using the 12-m Array and an efficient tuning of ALMA to optimize its use as a redshift hunter, with 73 per cent of the sources having a robust redshift identification. Nine of these redshift identifications also rely on observations from the Atacama Compact Array. The spectroscopic redshifts span a range 1.41 < z < 4.53 with a mean value of 2.75, and the CO emission line full-width at half-maxima range between 110, km, s-1 < FWHM < 1290, km, s-1 with a mean value of ∼500 km s-1, in line with other high-z samples. The derived CO(1-0) luminosity is significantly elevated relative to line-width to CO(1-0) luminosity scaling relation, which is suggestive of lensing magnification across our sources. In fact, the distribution of magnification factors inferred from the CO equivalent widths is consistent with expectations from galaxy-galaxy lensing models, though there is a hint of an excess at large magnifications that may be attributable to the additional lensing optical depth from galaxy groups or clusters.

DOI： 10.1093/mnras/stac150

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

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We present two bright galaxy candidates at z ∼ 12–13 identified in our H-dropout Lyman break selection with 2.3 deg² near-infrared deep imaging data. These galaxy candidates, selected after careful screening of foreground interlopers, have spectral energy distributions showing a sharp discontinuity around 1.7 μm, a flat continuum at 2–5 μm, and nondetections at &lt;1.2 μm in the available photometric data sets, all of which are consistent with a z &gt; 12 galaxy. An ALMA program targeting one of the candidates shows a tentative 4σ [O iii] 88 μm line at z = 13.27, in agreement with its photometric redshift estimate. The number density of the z ∼ 12–13 candidates is comparable to that of bright z ∼ 10 galaxies and is consistent with a recently proposed double-power-law luminosity function rather than the Schechter function, indicating little evolution in the abundance of bright galaxies from z ∼ 4 to 13. Comparisons with theoretical models show that the models cannot reproduce the bright end of rest-frame ultraviolet luminosity functions at z ∼ 10–13. Combined with recent studies reporting similarly bright galaxies at z ∼ 9–11 and mature stellar populations at z ∼ 6–9, our results indicate the existence of a number of star-forming galaxies at z &gt; 10, which will be detected with upcoming space missions such as the James Webb Space Telescope, Nancy Grace Roman Space Telescope, and GREX-PLUS.

DOI： 10.3847/1538-4357/ac53a9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Astronomical Telescopes, Instruments, and Systems  

The next technological breakthrough in millimeter–submillimeter astronomy is three-dimensional imaging spectrometry with wide instantaneous spectral bandwidths and wide fields of view. The total optimization of the focal-plane instrument, the telescope, the observing strategy, and the signal-processing software must enable efficient removal of foreground emission from the Earth’s atmosphere, which is time-dependent and highly nonlinear in frequency. Here, we present Time-dependent End-to-end Model for Post-process Optimization (TiEMPO) of the DEep Spectroscopic HIgh-redshift MApper (DESHIMA) spectrometer. TiEMPO utilizes a dynamical model of the atmosphere and parameterized models of the astronomical source, the telescope, the instrument, and the detector. The output of TiEMPO is a time stream of sky brightness temperature and detected power, which can be analyzed by standard signal-processing software. We first compare TiEMPO simulations with an on-sky measurement by the wideband DESHIMA spectrometer, and find good agreement in the noise and sensitivity. We then use TiEMPO to simulate the detection of the line emission spectrum of a high-redshift galaxy using the DESHIMA 2.0 spectrometer in development. The TiEMPO model is open source. Its modular and parametrized design enables users to adapt it to optimize the end-to-end performance of spectroscopic and photometric instruments on existing and future telescopes

DOI： 10.1117/1.JATIS.8.2.028005

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

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Active galactic nucleus (AGN) feedback is postulated as a key mechanism for regulating star formation within galaxies. Studying the physical properties of the outflowing gas from AGNs is thus crucial for understanding the coevolution of galaxies and supermassive black holes. Here we report 55 pc resolution ALMA neutral atomic carbon [C i] ³P₁−³P₀ observations toward the central 1 kpc of the nearby Type 2 Seyfert galaxy NGC 1068, supplemented by 55 pc resolution CO(J = 1−0) observations. We find that [C i] emission within the central kiloparsec is strongly enhanced by a factor of &gt;5 compared to the typical [C i]/CO intensity ratio of ∼0.2 for nearby starburst galaxies (in units of brightness temperature). The most [C i]-enhanced gas (ratio &gt; 1) exhibits a kiloparsec-scale elongated structure centered at the AGN that matches the known biconical ionized gas outflow entraining molecular gas in the disk. A truncated, decelerating bicone model explains well the kinematics of the elongated structure, indicating that the [C i] enhancement is predominantly driven by the interaction between the ISM in the disk and the highly inclined ionized gas outflow (which is likely driven by the radio jet). Our results strongly favor the “CO dissociation scenario” rather than the “in situ C formation” one, which prefers a perfect bicone geometry. We suggest that the high-[C i]/CO intensity ratio gas in NGC 1068 directly traces ISM in the disk that is currently dissociated and entrained by the jet and the outflow, i.e., the “negative” effect of the AGN feedback.

DOI： 10.3847/2041-8213/ac59ae

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1093/pasj/psab129

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2628269

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2628600

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing Ltd  

We present new Atacama Large Millimeter/submillimeter Array Band 7 observational results of a Lyman-break galaxy at z = 7.15, B14-65666 ("Big Three Dragons"), which is an object detected in [O III] 88 mu m, [CII] 158 mu m, and dust continuum emission during the epoch of reionization. Our targets are the [N II] 122 mu m fine-structure emission line and the underlying 120 mu m dust continuum. The dust continuum is detected with a similar to 19 sigma significance. From far-infrared spectral energy distribution sampled at 90, 120, and 160 mu m, we obtain a best-fit dust temperature of 40 K (79 K) and an infrared luminosity of log(10)(L-IR/L-circle dot)=11.6 <i (12.1) at the emissivity index beta = 2.0 (1.0). The [N II] 122 mu m line is not detected. The 3 sigma upper limit of the [N II] luminosity is 8.1 x 10(7) L-circle dot. From the [N II], [O III], and [C II] line luminosities, we use the Cloudy photoionization code to estimate nebular parameters as functions of metallicity. If the metallicity of the galaxy is high (Z > 0.4 Z(circle dot)), the ionization parameter and hydrogen density are log(10)U similar or equal to-2.7 +/- 0.1 n(H) similar or equal to 50-250 cm(-3), respectively, which are comparable to those measured in low-redshift galaxies. The nitrogen-to-oxygen abundance ratio, N/O, is constrained to be subsolar. At Z < 0.4 Z(circle dot), the allowed U drastically increases as the assumed metallicity decreases. For high ionization parameters, the N/O constraint becomes weak. Finally, our Cloudy models predict the location of B14-65666 on the BPT diagram, thereby allowing a comparison with low-redshift galaxies.

DOI： 10.3847/1538-4357/ac2a36

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DOI： 10.3847/1538-4357/ac20d5

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We report ALMA Band 9 continuum observations of the normal, dusty star-forming galaxy A1689-zD1 at z = 7.13, resulting in a ∼4.6 σ detection at 702 GHz. For the first time, these observations probe the far-infrared spectrum shortward of the emission peak of a galaxy in the Epoch of Reionization (EoR). Together with ancillary data from earlier works, we derive the dust temperature, Td, and mass, Md, of A1689-zD1 using both traditional modified blackbody spectral energy density fitting, and a new method that relies only on the [C ii] 158 μm line and underlying continuum data. The two methods give Td = (42+13-7, 40+13-) K, and Md} = (1.7+1.3-0.7, 2.0+1.8-1.0), ×, 107, M⊙. Band 9 observations improve the accuracy of the dust temperature (mass) estimate by ∼50 per cent (6 times). The derived temperatures confirm the reported increasing Td-redshift trend between z = 0 and 8; the dust mass is consistent with a supernova origin. Although A1689-zD1 is a normal UV-selected galaxy, our results, implying that ∼85 per cent of its star-formation rate is obscured, underline the non-negligible effects of dust in EoR galaxies.

DOI： 10.1093/mnrasl/slab104

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We report ALMA Band 9 continuum observations of the normal, dusty star-forming galaxy A1689-zD1 at z = 7.13, resulting in a ∼4.6 σ detection at 702 GHz. For the first time, these observations probe the far-infrared spectrum shortward of the emission peak of a galaxy in the Epoch of Reionization (EoR). Together with ancillary data from earlier works, we derive the dust temperature, Td, and mass, Md, of A1689-zD1 using both traditional modified blackbody spectral energy density fitting, and a new method that relies only on the [C ii] 158 μm line and underlying continuum data. The two methods give Td=(42^+13−7,40^+13−7⁠) K, and Md=(1.7^+1.3−0.7,2.0^+1.8−1.0)×10^7M⊙⁠. Band 9 observations improve the accuracy of the dust temperature (mass) estimate by ∼50 per cent (6 times). The derived temperatures confirm the reported increasing Td-redshift trend between z = 0 and 8; the dust mass is consistent with a supernova origin. Although A1689-zD1 is a normal UV-selected galaxy, our results, implying that ∼85 per cent of its star-formation rate is obscured, underline the non-negligible effects of dust in EoR galaxies.

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

For submillimeter spectroscopy with ground-based single-dish telescopes, removing the noise contribution from the Earth's atmosphere and the instrument is essential. For this purpose, here we propose a new method based on a data-scientific approach. The key technique is statistical matrix decomposition that automatically separates the signals of astronomical emission lines from the drift noise components in the fast-sampled (1-10 Hz) time-series spectra obtained by a position-switching (PSW) observation. Because the proposed method does not apply subtraction between two sets of noisy data (i.e., on-source and off-source spectra), it improves the observation sensitivity by a factor of 2 . It also reduces artificial signals such as baseline ripples on a spectrum, which may also help to improve the effective sensitivity. We demonstrate this improvement by using the spectroscopic data of emission lines toward a high-redshift galaxy observed with a 2 mm receiver on the 50 m Large Millimeter Telescope. Since the proposed method is carried out offline and no additional measurements are required, it offers an instant improvement on the spectra reduced so far with the conventional method. It also enables efficient deep spectroscopy driven by the future 50 m class large submillimeter single-dish telescopes, where fast PSW observations by mechanical antenna or mirror drive are difficult to achieve.

DOI： 10.3847/1538-3881/ac11f7

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present observations of a giant Lyα blob (LAB) in the SSA22 protocluster at z = 3.1, SSA22-LAB1, taken with the Atacama Large Millimeter/submillimeter Array. Dust continuum, along with [C II] 158 μm and CO(4–3) line emission have been detected in LAB1, showing complex morphology and kinematics across a ∼100 kpc central region. Seven galaxies at z = 3.0987–3.1016 in the surroundings are identified in [C II] and dust continuum emission, with two of them potential companions or tidal structures associated with the most massive galaxies. Spatially resolved [C II] and infrared luminosity ratios for the widely distributed media (L[CII]/LIR ≈ 10-2-10-3) suggest that the observed extended interstellar media are likely to have originated from star formation activity and the contribution from shocked gas is probably not dominant. LAB1 is found to harbor a total molecular gas mass Mmol = (8.7 ± 2.0) × 1010 Me, concentrated in the core region of the Lyα-emitting area. While (primarily obscured) star formation activity in the LAB1 core is one of the most plausible power sources for the Lyα emission, multiple major mergers found in the core may also play a role in making LAB1 exceptionally bright and extended in Lyα as a result of cooling radiation induced by gravitational interactions.

DOI： 10.3847/1538-4357/ac1106

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We report a massive quiescent galaxy at zspec= -3.0922+0.008-0.004 spectroscopically confirmed at a protocluster in the SSA22 field by detecting the Balmer and Ca II absorption features with the multi-object spectrometer for infrared exploration on the Keck I telescope. This is the most distant quiescent galaxy confirmed in a protocluster to date. We fit the optical to mid-infrared photometry and spectrum simultaneously with spectral energy distribution (SED) models of parametric and nonparametric star formation histories (SFHs). Both models fit the observed SED well and confirm that this object is a massive quiescent galaxy with a stellar mass of log (M∗/M⊙=11.26+0.03-0.04 and 11.54+0.03-0.00 and a star formation rate of SFR/M⊙ yr-1 < 0.3 and = -0.01+0.03-0.01 for parametric and nonparametric models, respectively. The SFH from the former modeling is described as an instantaneous starburst whereas that of the latter modeling is longer-lived, but both models agree with a sudden quenching of the star formation at ~0.6 Gyr ago. This massive quiescent galaxy is confirmed in an extremely dense group of galaxies predicted as a progenitor of a brightest cluster galaxy formed via multiple mergers in cosmological numerical simulations. We discover three new plausible [O III]λ5007 emitters at 3.0791 ≤ zspec ≤ 3.0833 serendipitously detected around the target. Two of them just between the target and its nearest massive galaxy are possible evidence of their interactions. They suggest the future great size and stellar mass evolution of this massive quiescent galaxy via mergers.

DOI： 10.3847/1538-4357/ac0cf8

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present a detailed investigation of millimeter-wave line emitters ALMA J010748.3-173028 (ALMA-J0107a) and ALMA J010747.0-173010 (ALMA-J0107b), which were serendipitously uncovered in the background of the nearby galaxy VV 114 with spectral scan observations at λ = 2-3 mm. Via Atacama Large Millimeter/submillimeter Array (ALMA) detection of CO(4-3), CO(3-2), and [C i](1-0) lines for both sources, their spectroscopic redshifts are unambiguously determined to be z = 2.4666 0.0002 and z = 2.3100 0.0002, respectively. We obtain the apparent molecular gas masses M gas of these two line emitters from [C i] line fluxes as (11.2 3.1) 1010 M o˙ and (4.2 1.2) 1010 M o˙, respectively. The observed CO(4-3) velocity field of ALMA-J0107a exhibits a clear velocity gradient across the CO disk, and we find that ALMA-J0107a is characterized by an inclined rotating disk with a significant turbulence, that is, a deprojected maximum rotation velocity to velocity dispersion ratio of 1.3 0.3. We find that the dynamical mass of ALMA-J0107a within the CO-emitting disk computed from the derived kinetic parameters, (1.1 0.2) 1010 M o˙, is an order of magnitude smaller than the molecular gas mass derived from dust continuum emission, (3.2 1.6) 1011 M o˙. We suggest this source is magnified by a gravitational lens with a magnification of μ ⪆ 10, which is consistent with the measured offset from the empirical correlation between CO-line luminosity and width.

DOI： 10.3847/1538-4357/ac01cc

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Progress of Theoretical and Experimental Physics  

The Laser Interferometer Gravitational-wave Observatory Scientific Collaboration and Virgo Collaboration (LVC) sent out 56 gravitational-wave (GW) notices during the third observing run (O3). The Japanese Collaboration for Gravitational wave ElectroMagnetic follow-up (J-GEM) performed optical and near-infrared observations to identify and observe an electromagnetic (EM) counterpart. We constructed a web-based system that enabled us to obtain and share information on candidate host galaxies for the counterpart, and the status of our observations. Candidate host galaxies were selected from the GLADE catalog with a weight based on the 3D GW localization map provided by LVC. We conducted galaxy-targeted and wide-field blind surveys, real-time data analysis, and visual inspection of observed galaxies. We performed galaxy-targeted follow-ups to 23 GW events during O3, and the maximum probability covered by our observations reached 9.8%. Among these, we successfully started observations for 10 GW events within 0.5 days after the detection. This result demonstrates that our follow-up observation has the potential to constrain EM radiation models for a merger of binary neutron stars at a distance of up to ∼100 Mpc with a probability area of ≤ 500 deg 2.

DOI： 10.1093/ptep/ptab007

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We report the time variability of the late-time radio emission in a Type I superluminous supernova (SLSN), PTF10hgi, at z = 0.0987. The Karl G. Jansky Very Large Array 3 GHz observations at 8.6 and 10 yr after the explosion both detected radio emission with a ∼40% decrease in flux density in the second epoch. This is the first report of a significant variability of the late-time radio light curve in an SLSN. Through combination with previous measurements in two other epochs, we constrained both the rise and decay phases of the radio light curve over three years, peaking at approximately 8-9 yr after the explosion with a peak luminosity of L3 GHz = 2 &times; 1021WHz-1. Possible scenarios for the origin of the variability are an active galactic nucleus (AGN) in the host galaxy, an afterglow caused by the interaction between an off-axis jet and circumstellar medium, and a wind nebula powered by a newly born magnetar. Comparisons with models show that the radio light curve can be reproduced by both the afterglow model and magnetar wind nebula model. Considering the flat radio spectrum at 1-15 GHz and an upper limit at 0.6 GHz obtained in previous studies, plausible scenarios are a low-luminosity flat-spectrum AGN or a magnetar wind nebula with a shallow injection spectral index. &copy; 2021 The American Astronomical Society. All rights reserved.

DOI： 10.3847/2041-8213/abef03

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We revisit the cold gas contents of galaxies in a protocluster at z = 2.49 using the lowest neutral atomic carbon transition [C i] 3 P 1 - 3 P 0 from Atacama Large Millimeter/submillimeter Array observations. We aim to test if the same gas-mass calibration adopted in field galaxies can be applied to protocluster galaxies. Five galaxies out of 16 targeted galaxies are detected in the [C i] line, and these are all previously detected in CO (3-2) and CO (4-3) and three in 1.1 mm dust continuum. We investigate the line luminosity relations between CO and [C i] in the protocluster and compare with other previous studies. We then compare the gas mass based on three gas tracers of [C i], CO(3-2), and dust if at least one of the last two tracers are available. Using the calibration adopted for field main-sequence galaxies, the [C i]-based gas measurements are lower than or comparable to the CO-based gas measurements by -0.35 dex at the lowest with the mean deviation of -0.14 dex. The differences between [C i]- and the dust- based measurements are relatively mild by up to 0.16 dex with the mean difference of 0.02 dex. Taking these all together with calibration uncertainties, with the [C i] line, we reconfirm our previous findings that the mean gas fraction is comparable to field galaxies for a stellar-mass range of . However, at least for these secure five detections, the depletion timescale decreases more rapidly with stellar mass than field galaxies that might be related to earlier quenching in dense environments.

DOI： 10.3847/1538-4357/abdbb5

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

<italic>Context.</italic> Characterizing the galaxy population in the early Universe holds the key to understanding the evolution of these objects and the role they played in cosmic reionization. However, there have been very few observations at the very highest redshifts to date.


<italic>Aims.</italic> In order to shed light on the properties of galaxies in the high-redshift Universe and their interstellar media, we observe the Lyman-<italic>α</italic> emitting galaxy <ext-link ext-link-type="aoi">z7_GSD_3811</ext-link> at <italic>z</italic> = 7.664 with bands 6 and 8 at the Atacama Large Millimeter/submillimeter Array (ALMA).


<italic>Methods.</italic> We target the far-infrared [O <sc>III</sc>] 88 <italic>μ</italic>m and [C <sc>II</sc>] 158 <italic>μ</italic>m emission lines and dust continuum in the star-forming galaxy z7_GSD_3811 with ALMA. We combine these measurements with earlier observations in the rest-frame ultraviolet (UV) in order to characterize the object and compare the results to those of earlier studies that observed [O <sc>III</sc>] and [C <sc>II</sc>] emission in high-redshift galaxies.


<italic>Results.</italic> The [O <sc>III</sc>] 88 <italic>μ</italic>m and [C <sc>II</sc>] 158 <italic>μ</italic>m emission lines are undetected at the position of z7_GSD_3811, with 3<italic>σ</italic> upper limits of 1.6  ×  10⁸ <italic>L</italic>_⊙ and 4.0  ×  10⁷ <italic>L</italic>_⊙, respectively. We do not detect any dust continuum in band 6 nor band 8. The measured rms in the band 8 and band 6 continua are 26 and 9.9 <italic>μ</italic>Jy beam⁻¹, respectively. Similar to several other high-redshift galaxies, z7_GSD_3811 exhibits low [C <sc>II</sc>] emission for its star formation rate compared to local galaxies. Furthermore, our upper limit on the [O <sc>III</sc>] line luminosity is lower than the previously observed [O <sc>III</sc>] lines in high-redshift galaxies with similar UV luminosities. Our ALMA band 6 and 8 dust continuum observations imply that z7_GSD_3811 likely has a low dust content, and our non-detections of the [O <sc>III</sc>] and [C <sc>II</sc>] lines could indicate that z7_GSD_3811 has a low metallicity (<italic>Z</italic> ≲ 0.1 <italic>Z</italic>_⊙).

DOI： 10.1051/0004-6361/202038180

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We present Atacama Large Millimeter/submillimeter Array [C ii] 158 μm line and far-infrared (FIR) continuum emission observations toward HSC J120505.09-000027.9 (J1205-0000) at z = 6.72 with a beam size of ∼0.″8 × 0.″5 (or 4.1 kpc × 2.6 kpc), the most distant red quasar known to date. Red quasars are modestly reddened by dust and are thought to be in rapid transition from an obscured starburst to an unobscured normal quasar, driven by powerful active galactic nucleus (AGN) feedback that blows out a cocoon of interstellar medium. The FIR continuum of J1205-0000 is bright, with an estimated luminosity of L FIR ∼ 3 × 1012 L o˙. The [C ii] line emission is extended on scales of r ∼ 5 kpc, greater than that of the FIR continuum. The line profiles at the extended regions are complex and broad (FWHM ∼ 630-780 km s-1). Although it is not practical to identify the nature of this extended structure, possible explanations include (i) companion/merging galaxies and (ii) massive AGN-driven outflows. For the case of (i), the companions are modestly star-forming (∼10 M o˙ yr-1) but are not detected by our Subaru optical observations (y AB,5σ = 24.4 mag). For the case of (ii), our lower limit to the cold neutral outflow rate is ∼100 M o˙ yr-1. The outflow kinetic energy and momentum are both much lower than predicted in energy-conserving wind models, suggesting that the AGN feedback in this quasar is not capable of completely suppressing its star formation.

DOI： 10.3847/1538-4357/abd7ef

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Other Link： https://iopscience.iop.org/article/10.3847/1538-4357/abd7ef/pdf

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2560789

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2560238

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

Purpose: As deformations of the main reflector of a radio telescope directly affect the observations, the evaluation of the deformation is extremely important. Dynamic characteristics of the main reflector of the Nobeyama 45 m Radio Telescope, Japan, are measured under two conditions: the first is when the pointing observation is in operation, and the second is when the reflector is stationary and is subjected to wind loads when the observation is out of operation. Methods: Dynamic characteristics of the main reflector are measured using piezoelectric accelerometers. Results and Conclusion: When the telescope is in operation, a vibration mode with one nodal line horizontally or vertically on the reflector is induced, depending on whether the reflector is moving in the azimuthal or elevational planes, whereas under windy conditions, vibration modes that have two to four nodal lines are simultaneously induced. The predominant mode is dependent on the direction of wind loads.

DOI： 10.1007/s42417-020-00202-9

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：EDP Sciences  

Deep surveys with the Atacama Large Millimeter Array (ALMA) have uncovered a population of dusty star-forming galaxies which are faint or even undetected at optical to near-infrared wavelengths. Their faintness at short wavelengths makes the detailed characterization of the population challenging. Here we present a spectroscopic redshift identification and a characterization of one of these near-infrared-dark galaxies discovered by an ALMA deep survey. The detection of [C <sc>I</sc>](1–0) and CO(4–3) emission lines determines the precise redshift of the galaxy, ADF22.A2, to be <italic>z</italic> = 3.9913 ± 0.0008. On the basis of a multi-wavelength analysis, ADF22.A2 is found to be a massive, star-forming galaxy with a stellar mass of <italic>M</italic>_∗ = 1.1_−0.6^+1.3 × 10¹¹ <italic>M</italic>_⊙ and SFR = 430₋₁₅₀⁺²³⁰ <italic>M</italic>_⊙ yr⁻¹. The molecular gas mass was derived to be <italic>M</italic>(H₂)^[CI] = (5.9 ± 1.5)×10¹⁰ <italic>M</italic>_⊙, indicating a gas fraction of ≈35%, and the ratios of <italic>L</italic>_[CI](1−0)/<italic>L</italic>_IR and <italic>L</italic>_[CI](1−0)/<italic>L</italic>_CO(4−3) suggest that the nature of the interstellar medium in ADF22.A2 is in accordance with those of other bright submillimeter galaxies. The properties of ADF22.A2, including the redshift, star-formation rate, stellar mass, and depletion time scale (<italic>τ</italic>_dep ≈ 0.1−0.2 Gyr), also suggest that ADF22.A2 has the characteristics expected for the progenitors of quiescent galaxies at <italic>z</italic> ≳ 3. Our results demonstrate the power of ALMA contiguous mapping and line scan, which help us to obtain an unbiased view of galaxy formation in the early Universe.

DOI： 10.1051/0004-6361/202038146

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

<title>Abstract</title>
We make use of the ALMA twenty-Six Arcmin2 survey of GOODS-S At One-millimeter (ASAGAO), deep 1.2 mm continuum observations of a 26-arcmin2 region in the Great Observatories Origins Deep Survey-South (GOODS-S) obtained with Atacama Large Millimeter/sub-millimeter Array (ALMA), to probe dust-enshrouded star formation in K-band selected (i.e., stellar mass selected) galaxies, which are drawn from the FourStar Galaxy Evolution Survey (ZFOURGE) catalog. Based on the ASAGAO combined map, which was created by combining ASAGAO and ALMA archival data in the GOODS-South field, we find that 24 ZFOURGE sources have 1.2 mm counterparts with a signal-to-noise ratio &amp;gt;4.5 (1σ ≃ 30–70 μJy beam−1 at 1.2 mm). Their median redshift is estimated to be $z$median = 2.38 ± 0.14. They generally follow the tight relationship of the stellar mass versus star formation rate (i.e., the main sequence of star-forming galaxies). ALMA-detected ZFOURGE sources exhibit systematically larger infrared (IR) excess (IRX ≡ LIR/LUV) compared to ZFOURGE galaxies without ALMA detections even though they have similar redshifts, stellar masses, and star formation rates. This implies the consensus stellar-mass versus IRX relation, which is known to be tight among rest-frame-ultraviolet-selected galaxies, cannot fully predict the ALMA detectability of stellar-mass-selected galaxies. We find that ALMA-detected ZFOURGE sources are the main contributors to the cosmic IR star formation rate density at $z$ = 2–3.

DOI： 10.1093/pasj/psaa057

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Other Link： http://academic.oup.com/pasj/article-pdf/72/4/69/33562710/psaa057.pdf

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

<title>Abstract</title>
We present the results of CO(1–0) observations of the host galaxy of a Type I superluminous supernova (SLSN-I), SN 2017egm, one of the closest SLSNe-I at z = 0.03063, by using the Atacama Large Millimeter/submillimeter Array. The molecular gas mass of the host galaxy is Mgas = (4.8 ± 0.3) × 109 M⊙, placing it on the sequence of normal star-forming galaxies in an Mgas–star-formation rate (SFR) plane. The molecular hydrogen column density at the location of SN 2017egm is higher than that of the Type II SN PTF10bgl, which is also located in the same host galaxy, and those of other Type II and Ia SNe located in different galaxies, suggesting that SLSNe-I have a preference for a dense molecular gas environment. On the other hand, the column density at the location of SN 2017egm is comparable to those of Type Ibc SNe. The surface densities of molecular gas and the SFR at the location of SN 2017egm are consistent with those of spatially resolved local star-forming galaxies and follow the Schmidt–Kennicutt relation. These facts suggest that SLSNe-I can occur in environments with the same star-formation mechanism as in normal star-forming galaxies.

DOI： 10.1093/pasj/psaa052

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Cambridge University Press (CUP)  

<title>Abstract</title>We present ALMA detection of the [O <sc>iii</sc>] 88 <italic>μ</italic>m line and 850 <italic>μ</italic>m dust continuum emission in a <italic>Y</italic>-dropout Lyman break galaxy, MACS0416_Y1. The [O <sc>iii</sc>] detection confirms the object with a spectroscopic redshift to be <italic>z</italic> = 8.3118±0.0003. The 850 <italic>μ</italic>m continuum intensity (0.14 mJy) implies a large dust mass on the order of 4×10⁶<italic>M</italic>_⊙. The ultraviolet-to-far infrared spectral energy distribution modeling, where the [O <sc>iii</sc>] emissivity model is incorporated, suggests the presence of a young (τ_age ≍ 4 Myr), star-forming (SFR ≍ 60<italic>M</italic>_⊙yr⁻¹), and moderately metal-polluted (<italic>Z</italic> ≍ 0.2<italic>Z</italic>_⊙) stellar component with a stellar mass of 3 × 10⁸<italic>M</italic>_⊙. An analytic dust mass evolution model with a single episode of star formation does not reproduce the metallicity and dust mass in ≍ 4 Myr, suggesting an underlying evolved stellar component as the origin of the dust mass.

DOI： 10.1017/s1743921319002436

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Other Link： http://stacks.iop.org/0004-637X/874/i=1/a=27?key=crossref.08977684a624e2093b8b0428fd4f056e

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DOI： 10.3847/1538-4357/ab94bd

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Cambridge University Press (CUP)  

<title>Abstract</title>We present a 4.7σ detection of the [OIII] 88 <italic>μ</italic>m line in a gravitationally-lensed Lyman break galaxy, RXC J2248-ID3, using the Atacama Large Millimeter/submillimeter Array (ALMA). We did not detect [CII] 158 <italic>μ</italic>m and rest-frame 90 <italic>μ</italic>m dust continuum emission, suggesting that the bulk of the interstellar medium (ISM) is ionized. Our two-component SED model combining the previous Hubble Space Telescope (HST) data and new photometry obtained from Very Large Telescope (VLT), Spitzer and ALMA suggests the presence of young (∼2 Myr) and mature (∼600 Myr) stellar components with the metallicity of <italic>Z</italic> = 0.2Z_⊙. Our findings are in contrast with previous results claiming a very young, metal-poor stellar component.

DOI： 10.1017/s174392131900245x

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<title>Abstract</title>We present ALMA [CII] line and far-infrared (FIR) continuum observations of seven <italic>z</italic> &gt; 6 low-luminosity quasars (<italic>M</italic>₁₄₅₀ &gt; −25 mag) discovered by our on-going Subaru Hyper Suprime-Cam survey. The [CII] line was detected in all targets with luminosities of ∼(2−10) × 10⁸ L_⊙, about one order of magnitude smaller than optically luminous quasars. Also found was a wide scatter of FIR continuum luminosity, ranging from <italic>L</italic>_FIR &lt; 10¹¹<italic>L</italic>_⊙ to ∼2 × 10¹²<italic>L</italic>_⊙. With the [CII]-based dynamical mass, we suggest that a significant fraction of low-luminosity quasars are located on or even below the local Magorrian relation, particularly at the massive end of the galaxy mass distribution. This is a clear contrast to the previous finding that luminous quasars tend to have overmassive black holes relative to the relation. Our result is expected to show a less-biased nature of the early co-evolution of black holes and their host galaxies.

DOI： 10.1017/s1743921319009487

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<title>Abstract</title>We have developed a new SED fitting tool specialized for frontier redshift galaxies. It is a common case for high-<italic>z</italic> galaxies that the available data are restricted to rich optical to near-infrared photometry and few far-infrared (FIR) data deep enough to detect the faint object (e.g., <italic>HST</italic>/WFC3 + <italic>Spitzer</italic>/IRAC + ALMA). In such situation, one cannot perform a complicated modeling of dust emission in FIR regime. We then adopt simple treatment for the dust emission using empirical LIRG templates. Instead, we adopt a sophisticated and physically motivated modeling for stellar and nebular emission parts in rest-frame UV-to-optical regime. Our new code fits not only broad band photometry but also spectral emission line flux. There is an option to fit observed SED with two templates with different physical properties. Our new code, PANHIT, is now in public, and was already applied to some high-<italic>z</italic> frontier galaxies.

DOI： 10.1017/s1743921319002606

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<title>Abstract</title>Recently huge amount of dust <italic>M</italic>_dust ≃ 10⁶⁻⁷<italic>M</italic>_⊙ in galaxies at <italic>z</italic> = 7–8 has been discovered by ALMA observations. The suggested timescale of the dust production was a few–several×10⁸ yr, while the stellar mass was several × 10⁹<italic>M</italic>_⊙. This amount of dust cannot be easily explained only by a supply from supernovae if we consider the dust destruction by reverse shocks. We propose that these values can be consistently explained if we take into account the grain growth in the interstellar medium (ISM). This scenario successfully reproduces the evolution of the dust mass, as well as the SFR, and stellar mass simultaneously. We conclude that even at such an early epoch of the Universe, the dust grain growth in the ISM plays a significant role in galaxies.

DOI： 10.1017/s1743921319003107

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

We are developing an ultra-wideband spectroscopic instrument, DESHIMA (DEep Spectroscopic HIgh-redshift MApper), based on the technologies of an on-chip filter bank and microwave kinetic inductance detector (MKID) to investigate dusty starburst galaxies in the distant universe at millimeter and submillimeter wavelengths. An on-site experiment of DESHIMA was performed using the ASTE 10-m telescope. We established a responsivity model that converts frequency responses of the MKIDs to line-of-sight brightness temperature. We estimated two parameters of the responsivity model using a set of skydip data taken under various precipitable water vapor (PWV 0.4-3.0 mm) conditions for each MKID. The line-of-sight brightness temperature of sky is estimated using an atmospheric transmission model and the PWVs. As a result, we obtain an average temperature calibration uncertainty of 1 sigma=4, which is smaller than other photometric biases. In addition, the average forward efficiency of 0.88 in our responsivity model is consistent with the value expected from the geometrical support structure of the telescope. We also estimate line-of-sight PWVs of each skydip observation using the frequency response of MKIDs and confirm the consistency with PWVs reported by the Atacama Large Millimeter/submillimeter Array.

DOI： 10.1007/s10909-020-02338-0

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Other Link： http://link.springer.com/article/10.1007/s10909-020-02338-0/fulltext.html

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DOI： 10.1093/mnras/staa509

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/ab7992

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

<title>Abstract</title>
We propose a new observing method for single-dish millimeter and submillimeter spectroscopy using a heterodyne receiver equipped with a frequency-modulating local oscillator (FMLO). Unlike conventional switching methods, which extract astronomical signals by subtracting the reference spectra of off-sources from those of on-sources, the FMLO method does not need to obtain any off-source spectra; rather, it estimates them from the on-source spectra themselves. The principle uses high-dump-rate (10 Hz) spectroscopy with radio frequency modulation achieved by fast sweeping of a local oscillator of a heterodyne receiver. Because sky emission (i.e., off-source) fluctuates as $1/f$ and is spectrally correlated, it can be estimated and subtracted from time series spectra (a timestream) by principal component analysis. Meanwhile, astronomical signals remain in the timestream since they are modulated to a higher time-frequency domain. The FMLO method therefore achieves (1) a remarkably high observation efficiency, (2) reduced spectral baseline wiggles, and (3) software-based sideband separation. We developed an FMLO system for the Nobeyama $45\:$m telescope and a data reduction procedure for it. Frequency modulation was realized by a tunable and programmable first local oscillator. With observations of Galactic sources, we demonstrate that the observation efficiency of the FMLO method is dramatically improved compared to conventional switching methods. Specifically, we find that the time to achieve the same noise level is reduced by a factor of 3.0 in single-pointed observations and by a factor of 1.2 in mapping observations. The FMLO method can be applied to observations of fainter ($\sim$mK) spectral lines and larger ($\sim$deg$^{2}$) mapping. It offers much more efficient and baseline-stable observations compared to conventional switching methods.

DOI： 10.1093/pasj/psz121

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We present a conceptual study of a large format imaging spectrograph for next-generation large (50-m class) single-dish telescopes, i.e., the Large Submillimeter Telescope (LST) and Atacama Large Aperture Submillimeter Telescope (AtLAST). Recent discoveries of high-redshift star-forming galaxies at z=8-9 and candidate quiescent galaxies at z∼6 indicate the onset of earliest star formation just a few 100 million years after the Big Bang (i.e., z = 12-15), and LST/AtLAST will provide a unique pathway to uncover spectroscopically-identified ''first forming galaxies'' in the pre-reionization era, once it will be equipped with a large format imaging spectrograph. We describe the preliminary of 3-band, medium resolution (R=2000) imaging spectrograph with ∼1.5 M detectors in total based on the KATANA concept (Karatsu et al.∼2019), which exploits technologies of the integrated superconducting spectrometer (ISS) and a large-format imaging array like A-MKID.

DOI： 10.1117/12.2561238

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DOI： 10.1117/12.2561014

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of the International Astronomical Union  

The ALMA twenty-six arcmin2 survey of GOODS-S at one millimeter (ASAGAO) is a deep (1σ ∼61μJy/beam) and wide area (26 arcmin2) survey on a contiguous field at 1.2 mm. By combining with archival data, we obtained a deeper map in the same region (1σ ∼30μJy/beam-1, synthesized beam size 0.59″ × 0.53″), providing the largest sample of sources (25 sources at 5σ, 45 sources at 4.5σ) among ALMA blank-field surveys. The median redshift of the 4.5σ sources is 2.4. The number counts shows that 52% of the extragalactic background light at 1.2 mm is resolved into discrete sources. We create IR luminosity functions (LFs) at z = 1-3, and constrain the faintest luminosity of the LF at 2 < z < 3. The LFs are consistent with previous results based on other ALMA and SCUBA-2 observations, which suggests a positive luminosity evolution and negative density evolution.

DOI： 10.1017/S1743921319009542

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

<title>Abstract</title>
We present ALMA [C ii] line and far-infrared (FIR) continuum observations of three $z \gt 6$ low-luminosity quasars ($M_{\rm 1450} \gt -25$ mag) discovered by our Subaru Hyper Suprime-Cam (HSC) survey. The [C ii] line was detected in all three targets with luminosities of $(2.4\mbox{--}9.5) \times 10^8\, L_{\odot }$, about one order of magnitude smaller than optically luminous ($M_{\rm 1450} \lesssim -25$ mag) quasars. The FIR continuum luminosities range from $\lt 9 \times 10^{10}\, L_{\odot }$ (3 $\sigma$ limit) to ${\sim } 2 \times 10^{12}\, L_{\odot }$, indicating a wide range in star formation rates in these galaxies. Most of the HSC quasars studied thus far show [C ii]/ FIR luminosity ratios similar to local star-forming galaxies. Using the [C ii]-based dynamical mass ($M_{\rm dyn}$) as a surrogate for bulge stellar mass ($M_{\rm\, bulge}$), we find that a significant fraction of low-luminosity quasars are located on or even below the local $M_{\rm\, BH}$–$M_{\rm\, bulge}$ relation, particularly at the massive end of the galaxy mass distribution. In contrast, previous studies of optically luminous quasars have found that black holes are overmassive relative to the local relation. Given the low luminosities of our targets, we are exploring the nature of the early co-evolution of supermassive black holes and their hosts in a less biased way. Almost all of the quasars presented in this work are growing their black hole mass at a much higher pace at $z \sim 6$ than the parallel growth model, in which supermassive black holes and their hosts grow simultaneously to match the local $M_{\rm\, BH}$–$M_{\rm\, bulge}$ relation at all redshifts. As the low-luminosity quasars appear to realize the local co-evolutionary relation even at $z \sim 6$, they should have experienced vigorous starbursts prior to the currently observed quasar phase to catch up with the relation.

DOI： 10.1093/pasj/psz096

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We report on detections with the Atacama Large Millimeter/sub-millimeter Array of the far-infrared [O III] 88 μm line and the underlying dust continuum in two quasars in the reionization epoch, J205406.48-000514.8 (hereafter J2054-0005) at z = 6.0391 ± 0.0002 and J231038.88+185519.7 (hereafter J2310+1855) at z = 6.0035 ± 0.0007. The [O III] luminosities of J2054-0005 and J2310+1855 are L<SUB>[O III]</SUB> = (6.8 ± 0.6) × 10<SUP>9</SUP> and (2.4 ± 0.6) × 10<SUP>9</SUP> L<SUB>☉</SUB>, corresponding to ̃0.05% and 0.01% of the total infrared luminosity, L<SUB>TIR</SUB>, respectively. Combining these [O III] luminosities with [C II] 158 μm luminosities in the literature, we find that J2054-0005 and J2310+1855 have [O III]-to-[C II] luminosity ratios of 2.1 ± 0.4 and 0.3 ± 0.1, respectively, the latter of which is the lowest among objects so far reported at z &gt; 6. Combining [O III] observations at z ≈ 6-9 from our study and the literature, we identify the [O III] line deficit: objects with a larger L<SUB>TIR</SUB> (total infrared luminosity) have lower L<SUB>[O III]</SUB>-to-L<SUB>TIR</SUB> ratios. Furthermore, we also find that the anti-correlation is shifted toward a higher L<SUB>TIR</SUB> value when compared with the local [O III] line deficit....

DOI： 10.1093/pasj/psz094

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We report the first detection obtained with the Atacama Large Millimeter/submillimeter Array of the [N II] 122 μm line emission from a galaxy group BRI 1202-0725 at z = 4.69 consisting of a quasi-stellar object (QSO) and a submillimeter-bright galaxy (SMG). Combining this with a detection of [N II] 205 μm line in both galaxies, we constrain the electron densities of the ionized gas based on the line ratio of [N II] 122/205. The derived electron densities are {26}<SUB>-11</SUB><SUP>+12</SUP> and {134}<SUB>-39</SUB><SUP>+50</SUP> cm<SUP>-3</SUP> for the SMG and the QSO, respectively. The electron density of the SMG is similar to that of the Galactic Plane and to the average of the local spirals. However, higher electron densities (by up to a factor of three) could be possible for systematic uncertainties of the line flux estimates. The electron density of the QSO is comparable to high-z star-forming galaxies at z = 1.5-2.3, obtained using rest-frame optical lines and with the lower limits suggested from stacking analysis on lensed starbursts at z = 1-3.6 using the same tracer of [N II]. Our results suggest a large scatter of electron densities in global scale at fixed star formation rates for extreme starbursts. The success of the [N II] 122 μm and 205 μm detections at z = 4.69 demonstrates the power of future systematic surveys of extreme starbursts at z &gt; 4 for probing the interstellar medium conditions and the effects on surrounding environments....

DOI： 10.3847/2041-8213/ab412e

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We present our new ALMA observations targeting [OIII]88um, [CII]158um, [NII]122um, and dust continuum emission for three Lyman break galaxies at z=6.0293-6.2037 identified in the Subaru/Hyper Suprime-Cam survey. We clearly detect [OIII] and [CII] lines from all of the galaxies at 4.3-11.8sigma levels, and identify multi-band dust continuum emission in two of the three galaxies, allowing us to estimate infrared luminosities and dust temperatures simultaneously. In conjunction with previous ALMA observations for six galaxies at z&gt;6, we confirm that all the nine z=6-9 galaxies have high [OIII]/[CII] ratios of L[OIII]/L[CII]~3-20, ~10 times higher than z~0 galaxies. We also find a positive correlation between the [OIII]/[CII] ratio and the Lya equivalent width (EW) at the &gt;91% confidence level. We carefully investigate physical origins of the high [OIII]/[CII] ratios at z=6-9 using Cloudy, and find that high density of the interstellar medium, low C/O abundance ratio, and the cosmic microwave background attenuation are responsible to only a part of the z=6-9 galaxies. Instead, the observed high [OIII]/[CII] ratios are explained by 10-100 times higher ionization parameters or low photodissociation region (PDR) covering fractions of 0-10%, both of which are consistent with our [NII] observations. The latter scenario can be reproduced with a density bounded nebula with PDR deficit, which would enhance the Lya, Lyman continuum, and C+ ionizing photons escape from galaxies, consistent with the [OIII]/[CII]-Lya EW correlation we find. <P />...

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Language：Japanese   Publishing type：Research paper (scientific journal)  

We present a study of the gas kinematics of star-forming galaxies associated with protocluster 4C 23.56 at z = 2.49 using 0.″4 resolution CO (4-3) data taken with ALMA. Eleven Hα emitters (HAEs) are detected in CO (4-3), including six HAEs that were previously detected in CO (3-2) at a coarser angular resolution. The detections in both CO lines are broadly consistent in the line widths and the redshifts, confirming both detections. With an increase in the number of spectroscopic redshifts, we confirm that the protocluster is composed of two merging groups with a total halo mass of log (M <SUB>cl</SUB>/M <SUB>☉</SUB>) = 13.4-13.6, suggesting that the protocluster would evolve into a Virgo-like cluster (&gt;10<SUP>14</SUP> M <SUB>☉</SUB>). We compare the CO line widths and the CO luminosities with other (proto)clusters (n <SUB>gal</SUB> = 91) and general field (n <SUB>gal</SUB> = 80) galaxies from other studies. The 4C 23.56 protocluster galaxies have CO line widths and luminosities comparable to other protocluster galaxies on average. On the other hand, the CO line widths are on average broader by ≈50% compared to field galaxies, while the median CO luminosities are similar. The broader line widths can be attributed to both effects of unresolved gas-rich mergers and/or compact gas distribution, which is supported by our limited but decent angular resolution observations and the size estimate of three galaxies. Based on these results, we argue that gas-rich mergers may play a role in the retention of the specific angular momentum to a value similar to that of field populations during cluster assembly, though we need to verify this with a larger number of samples....

DOI： 10.3847/1538-4357/ab3b5b

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Language：English   Publishing type：Research paper (scientific journal)  

We report Atacama Large Millimetre/submillimeter Array (ALMA) Cycle-5
follow-up observations of two candidate [CII] emitters at z ~ 6 in the ALMA
deep field in SSA22 (ADF22). The candidates were detected blindly in a Cycle-2
ALMA survey covering ~ 5 square arcmins, with a single tuning, along with two
CO lines associated with galaxies at lower redshifts. Various tests suggested
at least one of the two > 6-sigma [CII] candidates should be robust (Hayatsu et
al. 2017). Nevertheless, our new, deeper observations recover neither
candidate, demonstrating a higher contamination rate than expected. The cause
of the spurious detections is under investigation but at present it remains
unclarified.

DOI： 10.3847/2515-5172/ab3228

arXiv

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We investigate the molecular gas in, and star-formation properties of, the
host galaxy (CGCG 137-068) of a mysterious transient, AT2018cow, at kpc and
larger scales, using archival band-3 data from the Atacama Large
Millimeter/submillimeter Array (ALMA). AT2018cow is the nearest Fast-Evolving
Luminous Transient (FELT), and this is the very first study unveiling
molecular-gas properties of FELTs. The achieved rms and beam size are 0.21 mJy
beam$^{-1}$ at a velocity resolution of $40$ km s$^{-1}$ and $3".66\times2".71$
($1.1~{\rm kpc} \times 0.8~{\rm kpc}$), respectively. CO($J$=1-0) emission is
successfully detected. The total molecular gas mass inferred from the CO data
is $(1.85\pm0.04)\times10^8$ M$_\odot$ with the Milky Way CO-to-H$_2$
conversion factor. The H$_2$ column density at the AT2018cow site is estimated
to be $8.6\times10^{20}$ cm$^{-2}$. The ALMA data reveal that (1) CGCG 137-068
is a normal star-forming (SF) dwarf galaxy in terms of its molecular gas and
star-formation properties and (2) AT2018cow is located between a CO peak and a
blue star cluster. These properties suggest on-going star formation and favor
the explosion of a massive star as the progenitor of AT2018cow. We also find
that CGCG 137-068 has a solar or super-solar metallicity. If the metallicity of
the other FELT hosts is not higher than average, then some property of SF dwarf
galaxies other than metallicity may be related to FELTs.

DOI： 10.3847/2041-8213/ab2915

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

The scatter in the relationship between the strength of [C II] 158 μm emission and the star formation rate at high redshift has been the source of much recent interest. Although the relationship is well established locally, several intensely star-forming galaxies have been found whose [C II] 158 μm emission is either weak, absent, or spatially offset from the young stars. Here we present new ALMA data for the two most distant gravitationally lensed and spectroscopically confirmed galaxies, A2744_YD4 at z = 8.38 and MACS1149_JD1 at z = 9.11, both of which reveal intense [O III] 88 μm emission. In both cases we provide stringent upper limits on the presence of [C II] 158 μm with respect to [O III] 88 μm. We review possible explanations for this apparent redshift-dependent [C II] deficit in the context of our recent hydrodynamical simulations. Our results highlight the importance of using several emission line diagnostics with ALMA to investigate the nature of the interstellar medium in early galaxies....

DOI： 10.1093/mnrasl/slz094

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Other Link： http://academic.oup.com/mnrasl/article-pdf/487/1/L81/28864236/slz094.pdf

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report detections of two 1.2 mm continuum sources (S <SUB>1.2 mm</SUB> ̃ 0.6 mJy) without any counterparts in the deep H- and/or K-band image (i.e., K-band magnitude ≳26 mag). These near-infrared-dark faint millimeter sources are uncovered by ASAGAO, a deep and wide-field (≃26 arcmin<SUP>2</SUP>) Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm survey. One has a red IRAC (3.6 and 4.5 μm) counterpart, and the other has been independently detected at 850 and 870 μm using SCUBA2 and ALMA Band 7, respectively. Their optical-to-radio spectral energy distributions indicate that they can lie at z ≳ 3-5 and can be in the early phase of massive galaxy formation. Their contribution to the cosmic star formation rate density is estimated to be ̃1 × 10<SUP>-3</SUP> M <SUB>☉</SUB> yr<SUP>-1</SUP> Mpc<SUP>-3</SUP> if they lie somewhere in the redshift range of z ̃ 3-5. This value can be consistent with, or greater than, that of bright submillimeter galaxies (S <SUB>870 μm</SUB> &gt; 4.2 mJy) at z ̃ 3-5. We also uncover three more candidate near-infrared-dark faint ALMA sources without any counterparts (S <SUB>1.2 mm</SUB> ̃ 0.45-0.86 mJy). These results show that an unbiased ALMA survey can reveal the dust-obscured star formation activities, which were missed in previous deep optical/near-infrared surveys....

DOI： 10.3847/1538-4357/ab0d22

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We present the results of CO(1-0) and CO(4-3) observations of the host galaxy
of a long-duration gamma-ray burst GRB080207 at z = 2.0858 by using the Karl G.
Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array.
The host is detected in CO(1-0) and CO(4-3), becoming the first case for a GRB
host with more than two CO transitions detected combined with CO(2-1) and
CO(3-2) in the literature. Adopting a metallicity-dependent CO-to-H2 conversion
factor, we derive a molecular gas mass of Mgas = 8.7 x 10^10 Modot, which
places the host in a sequence of normal star-forming galaxies in a
Mgas-star-formation rate (SFR) plane. A modified blackbody fit to the
far-infrared--millimeter photometry results in a dust temperature of 37 K and a
dust mass of Mdust = 1.5 x 10^8 Modot. The spatially-resolving CO(4-3)
observations allow us to examine the kinematics of the host. The CO velocity
field shows a clear rotation and is reproduced by a rotation-dominated disk
model with a rotation velocity of 350 km/s and a half-light radius of 2.4 kpc.
The CO spectral line energy distribution derived from the four CO transitions
is similar to that of starburst galaxies, suggesting a high excitation
condition. Comparison of molecular gas properties between the host and normal
(main-sequence) galaxies at similar redshifts shows that they share common
properties such as gas mass fraction, gas depletion timescale, gas-to-dust
ratio, location in the Mgas-SFR (or surface density) relation, and kinematics,
suggesting that long-duration GRBs can occur in normal star-forming
environments at z ~ 2.

DOI： 10.3847/1538-4357/ab1649

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present the results from Atacama Large Millimeter/submillimeter Array observations of [N II] 205 μm, [C II] 158 μm, and [O III] 88 μm lines in an unlensed submillimeter galaxy at z = 4.3, COSMOS-AzTEC-1, hosting a compact starburst core with an effective radius of ̃1 kpc. The [C II] and [N II] emission are spatially resolved in 0.″3-resolution (1 kpc in radius). The kinematic properties of the [N II] emission are consistent with those of the CO(4-3) and [C II] emission, suggesting that the ionized gas feels the same gravitational potential as the associated molecular gas and photodissociation regions (PDRs). On the other hand, the spatial extent is different among the lines and dust continuum: the [C II] emitting gas is the most extended and the dust is the most compact, leading to a difference of the physical conditions in the interstellar medium. We derive the incident far-ultraviolet flux and the hydrogen gas density through PDR modeling by properly subtracting the contribution of ionized gas to the total [C II] emission. The observed [C II] emission is likely produced by dense PDRs with {n}<SUB>{ { H</SUB> } }<SUP>PDR</SUP>}={10}<SUP>5.5{--</SUP>5.75} cm<SUP>-3</SUP> and G <SUB>0</SUB> = 10<SUP>3.5-3.75</SUP> in the central 1 kpc region and {n}<SUB>{ { H</SUB> } }<SUP>PDR</SUP>}={10}<SUP>5.0{--</SUP>5.25} cm<SUP>-3</SUP> and G <SUB>0</SUB> = 10<SUP>3.25-3.5</SUP> in the central 3 kpc region. We have also successfully measured the line ratio of [O III]/[N II] in the central 3 kpc region of COSMOS-AzTEC-1 at z = 4.3, which is the highest redshift where both nitrogen and oxygen lines are detected. Under the most likely physical conditions, the measured luminosity ratio of L <SUB>[O III]</SUB>/L <SUB>[N II]</SUB> = 6.4 ± 2.2 indicates a near solar metallicity with Z <SUB>gas</SUB> = 0.7-1.0 Z <SUB>☉</SUB>, suggesting a chemically evolved system at z = 4.3....

DOI： 10.3847/1538-4357/ab1415

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Language：English   Publishing type：Research paper (scientific journal)  

We argue that a 'sub-millimeter SDSS' - a sensitive large-area imaging+spectroscopic survey in the sub-mm window - will revolutionize our understanding of galaxy evolution in the early Universe. <P />...

arXiv

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We present the science case for mapping several thousand galaxy (proto)clusters at z=1-10 with a large aperture single dish sub-mm facility, producing a high-redshift counterpart to local large surveys of rich clusters like the well-studied Abell catalogue. <P />...

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Recent ALMA detection of the bright [OIII] 88 um line at z = 9.11, indicates the onset of star formation at z 15. In order to uncover a large number of z=10-15 galaxies, we argue two possible pathways: (1) a blind spectroscopic survey of [OIII] 88 um line emitters, and (2) a high-cadence survey of transient sources to catch the pop-III GRBs. <P />...

arXiv

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present the results from ALMA CO(3-2) observations of 66 Hα-selected galaxies in three protoclusters around radio galaxies: PKS 1138-262 (z = 2.16), USS 1558-003 (z = 2.53), and 4C 23.56 (z = 2.49). The pointing areas have an overdensity of ̃100 compared to the mean surface number density of galaxies in field environments. We detect the CO emission line in 16 star-forming galaxies, including six previously published galaxies, to measure the molecular gas mass. In the stellar mass range of 10.5 &lt; log (M<SUB>star</SUB>/M<SUB>☉</SUB>) &lt; 11.0, the protocluster galaxies have larger gas mass fractions and longer gas depletion timescales compared to the scaling relations established for field galaxies. On the other hand, the amounts of molecular gas in more massive galaxies with log (M<SUB>star</SUB>/M<SUB>☉</SUB>) &gt; 11.0 are comparable in mass to the scaling relation, or smaller. Our results suggest that the environmental effects on gas properties are mass dependent: in high-density environments, gas accretion through cosmic filaments is accelerated in less massive galaxies, while this is suppressed in the most massive system....

DOI： 10.1093/pasj/psz005

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.3847/1538-4357/aafa6f

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Cambridge University Press (CUP)  

We present the survey design, data reduction, construction of images, and source catalog of the Atacama Large Millimeter/submillimeter Array (ALMA) twenty-six arcmin<SUP>2</SUP> survey of GOODS-S at one millimeter (ASAGAO). ASAGAO is a deep (1 σ depth ̃ 61 μJy beam<SUP>-1</SUP> for a 250 kλ-tapered map with a synthesized beam size of 0{^''<SUB>.</SUB>}51 × 0{^''<SUB>.</SUB>}45) and wide area (26 arcmin<SUP>2</SUP>) survey on a contiguous field at 1.2 mm. By combining with ALMA archival data in the GOODS-South field, we obtained a deeper map in the same region (1 σ depth ̃ 30 μJy beam<SUP>-1</SUP> for a deep region with a 250 kλ-taper, and a synthesized beam size of 0{^''<SUB>.</SUB>}59 × 0{^''<SUB>.</SUB>}53), providing the largest sample of sources (25 sources at ≥5.0 σ, 45 sources at ≥4.5 σ) among ALMA blank-field surveys to date. The number counts show that 52^{+11}_{-8}% of the extragalactic background light at 1.2 mm is resolved into discrete sources at S<SUB>1.2 mm</SUB> &gt; 135 μJy. We create infrared (IR) luminosity functions (LFs) in the redshift range of z = 1-3 from the ASAGAO sources with K<SUB>s</SUB>-band counterparts, and constrain the faintest luminosity of the LF at 2.0 &lt; z &lt; 3.0. The LFs are consistent with previous results based on other ALMA and SCUBA-2 observations, which suggest a positive luminosity evolution and negative density evolution with increasing redshift. We find that obscured star-formation of sources with IR luminosities of log (L<SUB>IR</SUB>/L<SUB>☉</SUB>) ≳ 11.8 account for ≈60%-90% of the z ̃ 2 cosmic star-formation rate density....

DOI： 10.1093/pasj/psy104

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

We developed a simple add-on, cryogen-free, and low-power consumption calibrator for a new transition-edge sensor (TES) bolometer camera mounted on the ASTE 10-m telescope. To measure the responsivity of the TES bolometers and accurately correct for the nonlinearity and atmospheric extinction, we designed a motor-driven rotating filter wheel system installed in front of the cryostat window. This calibrator is required to cover the loading power under various atmospheric conditions, which corresponds to precipitable water vapor (PWV) of 0.5-4 mm. For this range of PWV, 25-100 K blackbodies are necessary for the observing bands of 1.1 and 0.85 mm. To simulate the temperature range, bolometers in the cryostat are also optically coupled to the low-temperature stage (&lt;4 K) inside the cryostat by spherical mirrors. In addition, we used moderately absorptive polystyrene plates that are placed between a spherical mirror and the cryostat window. Various combinations of filters result in eight different temperatures by the filter wheel system and simulate the atmospheric emission under various weather conditions at the ASTE site. <P />...

DOI： 10.1007/s10909-018-1916-1

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER/PLENUM PUBLISHERS  

We developed and deployed a simple add-on multi-temperature calibrator for our multicolor transition edge sensor (TES) bolometer camera aimed at simultaneous observation with observing wavelengths of 1.1 and 0.85 mm. To cover the power loading level from the atmospheric emission corresponding to precipitable water vapor (PWV) of 0.5-4 mm, the calibrator consists of spherical mirrors to show the low-temperature stages of the cryostat and filters with moderate opacity to mimic the eight-temperature cold blackbodies. The loading powers introduced by each filter were self-calibrated by measuring the load curves of the TES bolometers when a filter was placed in front of the cryostat window. Each science observation was preceded by the calibration process, which measures the response of the TES bolometers to the atmosphere and filters of various opacities. Then, the responsivities of TES bolometers were derived to convert their output signal to the loading power and correct for the nonlinearity inherent in its response. Furthermore, the loading power falling on the TES bolometers from atmospheric emission measured at various PWV was in good correlation with the PWV measured with the radiometer, which enables the atmospheric extinction correction by fast and sensitive bolometers compared to the available radiometers with the modest sampling speeds. <P />...

DOI： 10.1007/s10909-018-2009-x

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Recent observations with the Atacama Large Millimeter/submillimeter Array (ALMA) detected far-infrared emission lines such as the [O III] 88 μ m line from galaxies at z ̃ 7-9. We use a cosmological simulation of galaxy formation to study the physical properties of [O III] 88 μ m emitters. In a comoving volume of 50 h<SUP>-1</SUP> Mpc on a side, we locate 34 galaxies with stellar masses greater than 10^8 M_{☉} at z = 9, and more than 270 such galaxies at z = 7. We calculate the [O III] 88 μ m luminosities (L_{O III}, 88) by combining a physical model of H II regions with emission line calculations using the photoionization code CLOUDY. We show that the resulting L_{O III}, 88, for a given star formation rate, is slightly higher than predicted from the empirical relation for local galaxies, and is consistent with recent observations of galaxies at redshifts 7-9. Bright [O III] emitters with L_{O III}, 88 &gt; 10^8 L_{☉} have star formation rates higher than 3 M_{☉} yr^{-1}, and the typical metallicity is {̃ } 0.1 Z_{☉}. The galaxies are hosted by dark matter haloes with masses greater than 10^{11} M_{☉}. We propose to use the [O III] 5007 Å line, to be detected by James Webb Space Telescope, to study the properties of galaxies whose [O III] 88 μ m line emission has been already detected with ALMA....

DOI： 10.1093/mnrasl/sly167

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Language：Japanese   Publishing type：Research paper (scientific journal)  

On the basis of various data such as ALMA, JVLA, Chandra, Herschel, and Spitzer, we confirmed that two protostellar candidates in Oph A are bona fide protostars or proto-brown dwarfs (proto-BDs) in extremely early evolutionary stages. Both objects are barely visible across infrared (IR; i.e., near-IR to far-IR) bands. The physical nature of the cores is very similar to that expected in first hydrostatic cores (FHSCs), objects theoretically predicted in the evolutionary phase prior to stellar core formation with gas densities of ̃10<SUP>11-12</SUP> cm<SUP>-3</SUP>. This suggests that the evolutionary stage is close to the FHSC formation phase. The two objects are associated with faint X-ray sources, suggesting that they are in very early phase of stellar core formation with magnetic activity. In addition, we found the CO outflow components around both sources, which may originate from the young outflows driven by these sources. The masses of these objects are calculated to be ̃0.01-0.03 M <SUB>☉</SUB> from the dust continuum emission. These physical properties are consistent with that expected from the numerical model of forming brown dwarfs. These facts (the X-ray detection, CO outflow association, and FHSC-like spectral energy distributions) strongly indicate that the two objects are proto-BDs or will be in the very early phase of protostars, which will evolve to more massive protostars if they gain enough mass from their surroundings. The ages of these two objects are likely to be within ̃10<SUP>3</SUP> years after the protostellar core (or second core) formation, taking into account the outflow dynamical times (≲500 years)....

DOI： 10.3847/1538-4357/aae153

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Publishing type：Research paper (scientific journal)   Publisher：arXiv e-prints  

With the Atacama Large Millimeter/sub-millimeter Array (ALMA), we report detections of the far-infrared (FIR) [OIII] 88 $\mu$m line and the underlying dust continuum in the two quasars in the reionization epoch, J205406.48-000514.8 (hereafter J2054-0005) at $z=6.0391\pm0.0002$ and J231038.88+185519.7 (hereafter J2310+1855) at $z=6.0035\pm0.0007$. The [OIII] luminosity of J2054-0005 and J2310+1855 are $L_{\rm [OIII]} = (6.8\pm0.6) \times 10^{9}$ and $(2.4\pm0.6) \times 10^{9}$ $L_{\rm \odot}$, corresponding to $\approx$ 0.05\%\ and 0.01\%\ of the total infrared luminosity, $L_{\rm TIR}$, respectively. Combining these [OIII] luminosities with [CII] 158 $\mu$m luminosities in the literature, we find that J2054-0005 and J2310+1855 have the [OIII]-to-[CII] luminosity ratio of $2.1\pm0.4$ and $0.3\pm0.1$, respectively, the latter of which is the lowest among objects so far reported at $z&gt;6$. Combining [OIII] observations at $z\approx6-9$ from our study and the literature, we identify the [OIII] line deficit: objects with larger $L_{\rm TIR}$ have lower $L_{\rm [OIII]}$-to-$L_{\rm TIR}$ ratios. Furthermore, we also find that the anti-correlation is shifted toward higher $L_{\rm TIR}$ value when compared to the local [OIII] line deficit. <P />...

arXiv

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Language：English   Publishing type：Research paper (scientific journal)  

We present observations at 1.1 mm towards 16 powerful radio galaxies and a radio-quiet quasar at 0.5 &lt; z &lt; 6.3 acquired with the AzTEC camera mounted at the James Clerk Maxwell Telescope and Atacama Submillimeter Telescope Experiment to study the spatial distribution of submillimetre galaxies (SMGs) towards possible protocluster regions. The survey covers a total area of 1.01 sq deg with rms depths of 0.52-1.44 mJy and detects 728 sources above 3σ. We find overdensities of a factor of ̃2 in the source counts of three individual fields (4C+23.56, PKS1138-262, and MRC0355-037) over areas of ̃200 sq deg. When combining all fields, the source-count analysis finds an overdensity that reaches a factor ≳3 at S<SUB>1.1mm</SUB> ≥ 4 mJy covering a 1.5-arcmin-radius area centred on the active galactic nucleus. The large size of our maps allows us to establish that beyond a radius of 1.5 arcmin, the radial surface density of SMGs falls to that of a blank field. In addition, we find a trend for SMGs to align closely to a perpendicular direction with respect to the radio jets of the powerful central radio galaxies (73_{+13}^{-14} deg). This misalignment is found over projected comoving scales of 4-20 Mpc, departs from perfect alignment (0 deg) by ̃5σ, and apparently has no dependence on SMG luminosity. Under the assumption that the AzTEC sources are at the redshift of the central radio galaxy, the misalignment reported here can be interpreted as SMGs preferentially inhabiting mass-dominant filaments funnelling material towards the protoclusters, which are also the parent structures of the radio galaxies. <P />...

DOI： 10.1093/mnras/sty1714

arXiv

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Galaxies in the early Universe that are bright at submillimetre wavelengths (submillimetre-bright galaxies) are forming stars at a rate roughly 1,000 times higher than the Milky Way. A large fraction of the new stars form in the central kiloparsec of the galaxy<SUP>1-3</SUP>, a region that is comparable in size to the massive, quiescent galaxies found at the peak of cosmic star-formation history<SUP>4</SUP> and the cores of present-day giant elliptical galaxies. The physical and kinematic properties inside these compact starburst cores are poorly understood because probing them at relevant spatial scales requires extremely high angular resolution. Here we report observations with a linear resolution of 550 parsecs of gas and dust in an unlensed, submillimetre-bright galaxy at a redshift of z = 4.3, when the Universe was less than two billion years old. We resolve the spatial and kinematic structure of the molecular gas inside the heavily dust-obscured core and show that the underlying gas disk is clumpy and rotationally supported (that is, its rotation velocity is larger than the velocity dispersion). Our analysis of the molecular gas mass per unit area suggests that the starburst disk is gravitationally unstable, which implies that the self-gravity of the gas is stronger than the differential rotation of the disk and the internal pressure due to stellar-radiation feedback. As a result of the gravitational instability in the disk, the molecular gas would be consumed by star formation on a timescale of 100 million years, which is comparable to gas depletion times in merging starburst galaxies<SUP>5</SUP>....

DOI： 10.1038/s41586-018-0443-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

To search for dust-obscured star-formation activity in the early Universe, it is essential to obtain a deep and wide submillimeter/millimeter map. The advent of the Atacama Large Millimeter/submillimeter Array (ALMA) has enabled us to obtain such maps with sufficiently high spatial resolution to be free from source confusion. We present a new 1.1 mm-wave map obtained by ALMA in the SSA22 field. The field contains a remarkable proto-cluster at z = 3.09; therefore, it is an ideal region to investigate the role of a large-scale cosmic web on dust-obscured star formation. The typical 1σ depth of our map is 73 μJy beam<SUP>-1</SUP> with a {0^{^''<SUB>.</SUB>}5} resolution. Combining the present survey with earlier, archived observations, we map an area of 20 arcmin<SUP>2</SUP> (71 comoving Mpc<SUP>2</SUP> at z = 3.09). Within the combined survey area we have detected 35 sources at a signal-to-noise ratio (S/N) &gt;5, with flux densities of S<SUB>1.1mm</SUB> = 0.43-5.6 mJy, equivalent to star-formation rates of ≳100-1000 M<SUB>☉</SUB> yr<SUP>-1</SUP> at z = 3.09, for a Chabrier initial mass function: 17 sources out of 35 are new detections. The cumulative number counts show an excess by a factor of three to five compared to blank fields. The excess suggests enhanced, dust-enshrouded star-formation activity in the proto-cluster on a 10 comoving Mpc scale, indicating accelerated galaxy evolution in this overdense region....

DOI： 10.1093/pasj/psy065

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We present morphological properties of dusty star-forming galaxies at z = 1-3 determined with the high-resolution (FWHM ̃ 0.″19) Atacama Large Milllimeter/submillimeter Array (ALMA) 1 mm map of our ASAGAO survey covering a 26 arcmin<SUP>2</SUP> area in GOODS-S. In conjunction with the ALMA archival data, our sample consists of 45 ALMA sources with infrared luminosity (L <SUB>IR</SUB>) range of ̃10<SUP>11</SUP>-10<SUP>13</SUP> L <SUB>☉</SUB>. To obtain an average rest-frame far-infrared (FIR) profile, we perform individual measurements and careful stacking of the ALMA sources using the uv-visibility method that includes positional-uncertainty and smoothing-effect evaluations through Monte Carlo simulations. We find that our sample has an average FIR-wavelength Sérsic index and effective radius of n <SUB>FIR</SUB> = 1.2 ± 0.2 and R <SUB>e,FIR</SUB> = 1.0-1.3 kpc, respectively, additionally with a point-source component at the center, indicative of the existence of active galactic nuclei. The average FIR profile agrees with a morphology of an exponential disk clearly distinguished from a de Vaucouleurs spheroidal profile (Sérsic index of 4). We also examine the rest-frame optical Sérsic index n <SUB>opt</SUB> and effective radius R <SUB>e,opt</SUB> with deep Hubble Space Telescope (HST) images. Interestingly, we obtain n <SUB>opt</SUB> = 0.9 ± 0.3 (≃n <SUB>FIR</SUB>) and R <SUB>e,opt</SUB> = 3.2 ± 0.6 kpc (&gt;R <SUB>e,FIR</SUB>), suggesting that the dusty disk-like structure is embedded within a larger stellar disk. The rest-frame UV and FIR data of HST and ALMA provide us with a radial profile of the total star formation rate (SFR), where the infrared SFR dominates over the UV SFR at the center. Under the assumption of a constant SFR, a compact stellar distribution in z ̃ 1-2 compact quiescent galaxies (cQGs) is well reproduced, while a spheroidal stellar morphology of cQGs (n <SUB>opt</SUB> = 4) is not, suggestive of other important mechanism(s) such as dynamical dissipation....

DOI： 10.3847/1538-4357/aac6c4

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE-INT SOC OPTICAL ENGINEERING  

The Mid-Infrared Multi-field Imager for gaZing at the UnKnown Universe (MIMIZUKU) is a mid-infrared camera and spectrograph developed as a first-generation instrument on the University of Tokyo Atacama Observatory (TAO) 6.5-m telescope. MIMIZUKU covers a wide wavelength range from 2 to 38 pm and has a unique optical device called Field Stacker which realizes accurate calibration of variable atmospheric transmittance with a few percent accuracy. By utilizing these capabilities, MIMIZUKU realizes mid-infrared long-term monitoring, which has not been challenged well.MIMIZUKU has three optical channels, called NIR, MIR-S, and MIR-L, to realize the wide wavelength coverage. The MIR-S channel, which covers 6.8-26 pm, has been completed by now. We are planning to perform engineering observations with this channel at the Subaru telescope before the completion of the TAO 6.5-m telescope. In this paper, we report the results of the laboratory tests to evaluate the optical and detector performances of the MIR-S channel. As a result, we confirmed a pixel scale of 0.12 arcsec/pix and a vignetting free field of view of 2.10 x1.18. The instrument throughputs for imaging modes are measured to be 20-30%. Those for N- and Q-band spectroscopy modes are 17 and 5%, respectively. As for the detector performance, we derived the quantum efficiency to be 40-50% in the mid-infrared wavelength region and measured the readout noise to be 3000-6000 electrons, which are larger than the spec value. It was found that this large readout noise degrades the sensitivity of MIMIZUKU by a factor of two.

DOI： 10.1117/12.2312443

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Language：Japanese   Publishing type：Research paper (scientific journal)  

We present our ALMA Cycle 4 measurements of the [C II] emission line and the underlying far-infrared (FIR) continuum emission from four optically low-luminosity (M<SUB>1450</SUB> &gt; -25) quasars at z ≳ 6 discovered by the Subaru Hyper Suprime Cam (HSC) survey. The [C II] line and FIR continuum luminosities lie in the ranges L_[C II] = (3.8-10.2)× 10<SUP>8</SUP> L_{☉} and L<SUB>FIR</SUB> = (1.2-2.0) × 10<SUP>11</SUP> L_{☉}, which are at least one order of magnitude smaller than those of optically-luminous quasars at z ≳ 6. We estimate the star formation rates (SFRs) of our targets as ≃ 23-40 M_{☉} yr<SUP>-1</SUP>. Their line and continuum-emitting regions are marginally resolved, and found to be comparable in size to those of optically-luminous quasars, indicating that their SFR or likely gas mass surface densities (key controlling parameter of mass accretion) are accordingly different. The L_[C II}]}/L_FIR ratios of the hosts, ≃ (2.2-8.7) × 10<SUP>-3</SUP>, are fully consistent with local star-forming galaxies. Using the [C II] dynamics, we derived their dynamical masses within a radius of 1.5-2.5 kpc as ≃ (1.4-8.2) × 10<SUP>10</SUP> M_{☉}. By interpreting these masses as stellar ones, we suggest that these faint quasar hosts are on or even below the star-forming main sequence at z ̃ 6, i.e., they appear to be transforming into quiescent galaxies. This is in contrast to the optically-luminous quasars at those redshifts, which show starburst-like properties. Finally, we find that the ratios of black hole mass to host galaxy dynamical mass of most of the low-luminosity quasars, including the HSC ones, are consistent with the local value. The mass ratios of the HSC quasars can be reproduced by a semi-analytical model that assumes merger-induced black hole host galaxy evolution....

DOI： 10.1093/pasj/psy026

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

DOI： 10.3847/1538-4357/aab616

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We present molecular gas reservoirs of eighteen galaxies associated with the
XMMXCS J2215.9-1738 cluster at z=1.46. From Band 7 and Band 3 data of the
Atacama Large Millimeter/submillimeter Array (ALMA), we detect dust continuum
emission at 870 um and CO J=2-1 emission line from 8 and 17 member galaxies
respectively within a cluster-centric radius of $R_{200}$. The molecular gas
masses derived from the CO and/or dust continuum luminosities show that the
fraction of molecular gas mass and the depletion time scale for the cluster
galaxies are larger than expected from the scaling relations of molecular gas
on stellar mass and offset from the main sequence of star-forming galaxies in
general fields. The galaxies closer to the cluster center in terms of both
projected position and accretion phase seem to show a larger deviation from the
scaling relations. We speculate that the environment of galaxy cluster helps
feed the gas through inflow to the member galaxies and also reduce the
efficiency of star formation. The stacked Band 3 spectrum of 12 quiescent
galaxies with stellar mass $\sim10^{11}$ M$_\odot$ within 0.5$R_{200}$ shows no
detection of CO emission line, giving the upper limit of molecular gas mass and
molecular gas fraction to be $<10^{10}$ M$_\odot$ and $<10$%, respectively.
Therefore, the massive galaxies in the cluster core quench the star formation
activity while consuming most of the gas reservoirs.

DOI： 10.3847/1538-4357/aab3e7

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We investigate the X-ray active galactic nucleus (AGN) properties of millimeter galaxies in the Great Observatories Origins Deep Survey South (GOODS-S) field detected with the Atacama Large Millimeter/submillimeter Array (ALMA), by utilizing the Chandra 7-Ms data, the deepest X-ray survey to date. Our millimeter galaxy sample comes from the ASAGAO survey covering 26 arcmin<SUP>2</SUP> (12 sources at a 1.2 mm flux-density limit of ≈ 0.6 mJy), supplemented by the deeper but narrower 1.3 mm survey of a part of the ASAGAO field by Dunlop et al. Ofthe 25 total millimeter galaxies, 14 have Chandra counterparts. The observed AGN fractions at z=1.5{--}3 are found to be {90}<SUB>-19</SUB><SUP>+8</SUP>% and {57}<SUB>-25</SUB><SUP>+23</SUP>% for the ultra-luminous and luminous infrared galaxies with log {L}<SUB>{IR</SUB>}/{L}<SUB>☉ </SUB> = 12-12.8 and log {L}<SUB>{IR</SUB>}/{L}<SUB>☉ </SUB> = 11.5-12, respectively. The majority (̃2/3) of the ALMA and/or Herschel detected X-ray AGNs at z = 1.5-3 appear to be star-formation-dominant populations, having {L}<SUB>{ { X</SUB> } }/ {L}<SUB>{IR</SUB>} ratios smaller than the “simultaneous evolution” value expected from the local black-hole-mass-to-stellar-mass ({M}<SUB>{BH</SUB>}-M <SUB>*</SUB>) relation. On the basis of the {L}<SUB>{ { X</SUB> } } and stellar mass relation, we infer that a large fraction of star-forming galaxies at z=1.5{--}3 have black hole masses that are smaller than those expected from the local {M}<SUB>{BH</SUB>}-M <SUB>*</SUB> relation. This contrasts previous reports on luminous AGNs at the same redshifts detected in wider and shallower surveys, which are subject to selection biases against lower luminosity AGNs. Our results are consistent with an evolutionary scenario in which star formation occurs first, and an AGN-dominant phase follows later, in objects that finally evolve into galaxies with classical bulges....

DOI： 10.3847/1538-4357/aa9f10

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Language：Japanese   Publishing type：Research paper (international conference proceedings)   Publisher：SPIE  

DOI： 10.1117/12.2310060

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We study the heating mechanisms and Lyα escape fractions of 35 Lyα blobs (LABs) at z ≈ 3.1 in the SSA22 field. Dust continuum sources have been identified in 11 of the 35 LABs, all with star formation rates (SFRs) above 100 M <SUB>☉</SUB> yr<SUP>-1</SUP>. Likely radio counterparts are detected in 9 out of 29 investigated LABs. The detection of submillimeter dust emission is more linked to the physical size of the Lyα emission than to the Lyα luminosities of the LABs. A radio excess in the submillimeter/radio-detected LABs is common, hinting at the presence of active galactic nuclei. Most radio sources without X-ray counterparts are located at the centers of the LABs. However, all X-ray counterparts avoid the central regions. This may be explained by absorption due to exceptionally large column densities along the line-of-sight or by LAB morphologies, which are highly orientation dependent. The median Lyα escape fraction is about 3% among the submillimeter-detected LABs, which is lower than a lower limit of 11% for the submillimeter-undetected LABs. We suspect that the large difference is due to the high dust attenuation supported by the large SFRs, the dense large-scale environment as well as large uncertainties in the extinction corrections required to apply when interpreting optical data....

DOI： 10.3847/1538-4357/aa960f

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

GW170817 is the first detected gravitational wave source from a neutron star merger. We present the Japanese collaboration for gravitational-wave electro-magnetic (J-GEM) follow-up observations of SSS17a, an electromagnetic counterpart of GW170817. SSS17a shows a 2.5mag decline in the z band during the period between 1.7 and 7.7 d after the merger. Such a rapid decline is not comparable with supernovae light curves at any epoch. The color of SSS17a also evolves rapidly and becomes redder during later epochs: the z - H color has changed by approximately 2.5mag during the period between 0.7 and 7.7 d. The rapid evolutions of both the color and the optical brightness are consistent with the expected properties of a kilonova that is powered by the radioactive decay of newly synthesized r-process nuclei. Kilonova models with Lanthanide elements can reproduce the aforementioned observed properties well, which suggests that r-process nucleosynthesis beyond the second peak takes place in SSS17a. However, the absolute magnitude of SSS17a is brighter than the expected brightness of the kilonova models with an ejectamass of 0.01M(circle dot), which suggests a more intensemass ejection (similar to 0.03M(circle dot)) or possibly an additional energy source.

DOI： 10.1093/pasj/psx118

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

Recent detection of gravitational waves from a neutron star (NS) merger event GW170817 and identification of an electromagnetic counterpart provide a unique opportunity to study the physical processes in NS mergers. To derive properties of ejected material from the NS merger, we perform radiative transfer simulations of kilonova, optical and near-infrared emissions powered by radioactive decays of r-process nuclei synthesized in the merger. We find that the observed near-infrared emission lasting for &gt;10 d is explained by 0.03 M<SUB>☉</SUB> of ejecta containing lanthanide elements. However, the blue optical component observed at the initial phases requires an ejecta component with a relatively high electron fraction (Y<SUB>e</SUB>). We show that both optical and near-infrared emissions are simultaneously reproduced by the ejecta with a medium Y<SUB>e</SUB> of ̃0.25. We suggest that a dominant component powering the emission is post-merger ejecta, which exhibits that the mass ejection after the first dynamical ejection is quite efficient. Our results indicate that NS mergers synthesize a wide range of r-process elements and strengthen the hypothesis that NS mergers are the origin of r-process elements in the Universe. <P />...

DOI： 10.1093/pasj/psx121

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We present an 8 pc x 5 pc resolution view of the central ~ 200 pc region of
the nearby starburst galaxy NGC 253, based on ALMA Band 7 ({\lambda} ~ 0.85 mm
or {\nu} ~ 350 GHz) observations covering 11 GHz. We resolve the nuclear
starburst of NGC 253 into eight dusty star-forming clumps, 10 pc in scale, for
the first time. These clumps, each of which contains (4-10) x 10^4 M_sun of
dust (assuming that the dust temperature is 25 K) and up to 6 x 10^2 massive
(O5V) stars, appear to be aligned in two parallel ridges, while they have been
blended in previous studies. Despite the similarities in sizes and dust masses
of these clumps, their line spectra vary drastically from clump to clump
although they are separated by only ~ 10 pc. Specifically, one of the clumps,
Clump 1, exhibits line confusion-limited spectra with at least 36 emission
lines from 19 molecules (including CH3OH, HNCO, H2CO, CH3CCH, H2CS, and H3O+)
and a hydrogen recombination line (H26{\alpha}), while much fewer kinds of
molecular lines are detected in some other clumps where fragile species, such
as complex organic molecules and HNCO, completely disappear from their spectra.
We demonstrate the existence of hot molecular gas ($T_rot (SO2) = 90 {\pm} 11
K) in the former clump, which suggests that the hot and chemically rich
environments are localized within a 10-pc scale star-forming clump.

DOI： 10.3847/1538-4357/aa8fd4

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We report the study of the far-infrared (IR) sizes of submillimeter galaxies (SMGs) in relation to their dust-obscured star formation rate (SFR) and active galactic nuclei (AGN) presence, determined using mid-IR photometry. We determined the millimeter-wave ({λ }<SUB>{obs</SUB>}=1100 μ m) sizes of 69 Atacama Large Millimeter/submillimeter Array (ALMA)-identified SMGs, selected with ≥slant 10σ confidence on ALMA images ({F}<SUB>1100μ { { m</SUB> } }=1.7-7.4 mJy). We found that all of the SMGs are located above an avoidance region in the size-flux plane, as expected by the Eddington limit for star formation. In order to understand what drives the different millimeter-wave sizes in SMGs, we investigated the relation between millimeter-wave size and AGN fraction for 25 of our SMGs at z = 1-3. We found that the SMGs for which the mid-IR emission is dominated by star formation or AGN have extended millimeter-sizes, with respective median {R}<SUB>{ { c</SUB>},{ { e } } }={1.6}<SUB>-0.21</SUB><SUP>+0.34</SUP> and {1.5}<SUB>-0.24</SUB><SUP>+0.93</SUP> kpc. Instead, the SMGs for which the mid-IR emission corresponds to star-forming/AGN composites have more compact millimeter-wave sizes, with median {R}<SUB>{ { c</SUB>},{ { e } } }={1.0}<SUB>-0.20</SUB><SUP>+0.20</SUP> kpc. The relation between millimeter-wave size and AGN fraction suggests that this size may be related to the evolutionary stage of the SMG. The very compact sizes for composite star-forming/AGN systems could be explained by supermassive black holes growing rapidly during the SMG coalescing, star-formation phase....

DOI： 10.3847/2041-8213/aa9572

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Other Link： https://iopscience.iop.org/article/10.3847/2041-8213/aa9572

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of similar to 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of 40(-8)(+8) Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M-circle dot. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at similar to 40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over similar to 10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position similar to 9 and similar to 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

DOI： 10.3847/2041-8213/aa91c9

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Other Link： https://iopscience.iop.org/article/10.3847/2041-8213/aa91c9/pdf

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We present the results of a blind millimeter line emitter search using ALMA
Band 6 data with a single frequency tuning toward four gravitational lensing
clusters (RXJ1347.5-1145, Abell S0592, MACS J0416.1-2403, and Abell 2744). We
construct three-dimensional signal-to-noise ratio (S/N) cubes with 60 MHz and
100 MHz binning, and search for millimeter line emitters. We do not detect any
line emitters with a peak S/N > 5, although we do find a line emitter candidate
with a peak S/N ~ 4.5. These results provide upper limits to the CO(3-2),
CO(4-3), CO(5-4), and [CII] luminosity functions at z ~ 0.3, 0.7, 1.2, and 6,
respectively. Because of the magnification effect of gravitational lensing
clusters, the new data provide the first constraints on the CO and [CII]
luminosity functions at unprecedentedly low luminosity levels, i.e., down to
$<~ 10^{-3}-10^{-1} $Mpc$^{-3}$ dex$^{-1}$ at $L'_{CO} ~ 10^8-10^{10}$ K km
$s^{-1}$ pc$^2$ and $<~ 10^{-3}-10^{-2}$ Mpc$^{-3}$ dex$^{-1}$ at $L_[CII] ~
10^8-10^{10} L_\odot$, respectively. Although the constraints to date are not
stringent yet, we find that the evolution of the CO and [CII] luminosity
functions are broadly consistent with the predictions of semi-analytical
models. This study demonstrates that the wide observations with a single
frequency tuning toward gravitational lensing clusters are promising for
constraining the CO and [CII] luminosity functions.

DOI： 10.3847/1538-4357/aa80e0

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We have investigated properties of the interstellar medium in interacting galaxies in early and mid stages using mapping data of <SUP>12</SUP>CO(J = 1-0) and H i. Assuming the standard CO-H<SUB>2</SUB> conversion factor, we found no difference in molecular gas mass, atomic gas mass, and total gas mass (the sum of atomic and molecular gas mass) between interacting galaxies and isolated galaxies. However, interacting galaxies have a higher global molecular gas fraction f_{mol}^{global} (the ratio of molecular gas mass to total gas mass averaged over a whole galaxy) at 0.71 ± 0.15 than isolated galaxies (0.52 ± 0.18). The distribution of the local molecular gas fraction f<SUB>mol</SUB>, the ratio of the surface density of molecular gas to that of the total gas, is different from the distribution in typical isolated galaxies. By a pixel-to-pixel comparison, isolated spiral galaxies show a gradual increase in f<SUB>mol</SUB> along the surface density of total gas until it is saturated at 1.0, while interacting galaxies show no clear relation. We performed pixel-to-pixel theoretical model fits by varying metallicity and external pressure. According to the model fitting, external pressure can explain the trend of f<SUB>mol</SUB> in the interacting galaxies. Assuming half of the standard CO-H<SUB>2</SUB> conversion factor for interacting galaxies, the results of pixel-to-pixel theoretical model fitting get worse than adopting the standard conversion factor, although f_{mol}^{global} of interacting galaxies (0.62 ± 0.17) becomes the same as in isolated galaxies. We conclude that external pressure occurs due to the shock prevailing over a whole galaxy or due to collisions between giant molecular clouds even in the early stage of the interaction. The external pressure accelerates an efficient transition from atomic gas to molecular gas. Regarding the chemical timescale, high f<SUB>mol</SUB> can be achieved at the very early stage of interaction even if the shock induced by the collision of galaxies ionizes interstellar gas. <P />...

DOI： 10.1093/pasj/psx041

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present long-baseline ALMA observations of the strong gravitational lens H-ATLAS J090740.0-004200 (SDP.9), which consists of an elliptical galaxy at {z}<SUB>{ { L</SUB> } }=0.6129 lensing a background submillimeter galaxy into two extended arcs. The data include Band 6 continuum observations, as well as CO J = 6-5 molecular line observations, from which we measure an updated source redshift of {z}<SUB>{ { S</SUB> } }=1.5747. The image morphology in the ALMA data is different from that of the Hubble Space Telescope (HST) data, indicating a spatial offset between the stellar, gas, and dust component of the source galaxy. We model the lens as an elliptical power law density profile with external shear using a combination of archival HST data and conjugate points identified in the ALMA data. Our best model has an Einstein radius of {θ }<SUB>{ { E</SUB> } }=0.66+/- 0.01 and a slightly steeper than isothermal mass profile slope. We search for the central image of the lens, which can be used constrain the inner mass distribution of the lens galaxy including the central supermassive black hole, but do not detect it in the integrated CO image at a 3σ rms level of 0.0471 Jy km s<SUP>-1</SUP>....

DOI： 10.3847/2041-8213/aa7d4a

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We investigate gas contents of star-forming galaxies associated with
protocluster 4C23.56 at z = 2.49 by using the redshifted CO(3-2) and 1.1 mm
dust continuum with the Atacama Large Millimeter/submillimeter Array. The
observations unveil seven CO detections out of 22 targeted H$\alpha$ emitters
(HAEs) and four out of 19 in 1.1 mm dust continuum. They have high stellar mass
($M_{\star}>4\times 10^{10}$ $M_{\odot}$) and exhibit a specific star-formation
rate typical of main-sequence star forming galaxies at $z\sim2.5$. Different
gas mass estimators from CO(3-2) and 1.1 mm yield consistent values for
simultaneous detections. The gas mass ($M_{\rm gas}$) and gas fraction ($f_{\rm
gas}$) are comparable to those of field galaxies, with $M_{\rm gas}=[0.3,
1.8]\times10^{11} \times (\alpha_{\rm CO}/(4.36\times A(Z)$)) M$_{\odot}$,
where $\alpha_{\rm CO}$ is the CO-to-H$_2$ conversion factor and $A(Z)$ the
additional correction factor for the metallicity dependence of $\alpha_{\rm
CO}$, and $\langle f_{\rm gas}\rangle = 0.53 \pm 0.07$ from CO(3-2). Our
measurements place a constraint on the cosmic gas density of high-$z$
protoclusters, indicating the protocluster is characterized by a gas density
higher than that of the general fields by an order of magnitude. We found $\rho
(H_2)\sim 5 \times 10^9 \,M_{\odot}\,{\rm Mpc^{-3 } }$ with the CO(3-2)
detections. The five ALMA CO detections occur in the region of highest galaxy
surface density, where the density positively correlates with global
star-forming efficiency (SFE) and stellar mass. Such correlations imply a
potentially critical role of environment on early galaxy evolution at high-z
protoclusters, although future observations are necessary for confirmation.

DOI： 10.3847/1538-4357/aa74c2

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We report a survey of molecular gas in galaxies in the XMMXCS J2215.9-1738 cluster at z = 1.46. We have detected emission lines from 17 galaxies within a radius of R <SUB>200</SUB> from the cluster center, in Band 3 data of the Atacama Large Millimeter/submillimeter Array, with a coverage of 93-95 GHz in frequency and 2.33 arcmin<SUP>2</SUP> in spatial direction. The lines are all identified as CO J = 2-1 emission lines from cluster members at z̃ 1.46 by their redshifts and the colors of their optical and near-infrared (NIR) counterparts. The line luminosities reach down to {L}<SUB>{CO</SUB>(2{--}1)}<SUP>\prime </SUP>=4.5× {10}<SUP>9</SUP> K km s<SUP>-1</SUP> pc<SUP>2</SUP>. The spatial distribution of galaxies with a detection of CO(2-1) suggests that they disappear from the very center of the cluster. The phase-space diagram showing relative velocity versus cluster-centric distance indicates that the gas-rich galaxies have entered the cluster more recently than the gas-poor star-forming galaxies and passive galaxies located in the virialized region of this cluster. The results imply that the galaxies experienced ram-pressure stripping and/or strangulation during the course of infall toward the cluster center and then the molecular gas in the galaxies at the cluster center was depleted by star formation....

DOI： 10.3847/2041-8213/aa71ad

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Language：Japanese   Publishing type：Research paper (scientific journal)  

We report the identification of four millimeter line-emitting galaxies with the Atacama Large Milli/submillimeter Array (ALMA) in SSA22 Field (ADF22). We analyze the ALMA 1.1-mm survey data, with an effective survey area of 5 arcmin<SUP>2</SUP>, frequency ranges of 253.1-256.8 and 269.1-272.8 GHz, angular resolution of 0{^''<SUB>.</SUB>}7 and rms noise of 0.8 mJy beam<SUP>-1</SUP> at 36 km s<SUP>-1</SUP> velocity resolution. We detect four line-emitter candidates with significance levels above 6σ. We identify one of the four sources as a CO(9-8) emitter at z = 3.1 in a member of the proto-cluster known in this field. Another line emitter with an optical counterpart is likely a CO(4-3) emitter at z = 0.7. The other two sources without any millimeter continuum or optical/near-infrared counterpart are likely to be [C II] emitter candidates at z = 6.0 and 6.5. The equivalent widths of the [C II] candidates are consistent with those of confirmed high-redshift [C II] emitters and candidates, and are a factor of 10 times larger than that of the CO(9-8) emitter detected in this search. The [C II] luminosity of the candidates are 4-7 × 10<SUP>8</SUP> L<SUB>☉</SUB>. The star formation rates (SFRs) of these sources are estimated to be 10-20 M<SUB>☉</SUB> yr<SUP>-1</SUP> if we adopt an empirical [C II] luminosity-SFR relation. One of them has a relatively low S/N ratio, but shows features characteristic of emission lines. Assuming that at least one of the two candidates is a [C II] emitter, we derive a lower limit of [C II]-based star formation rate density (SFRD) at z ̃ 6. The resulting value of &gt;10<SUP>-2</SUP> M<SUB>☉</SUB> yr<SUP>-1</SUP> Mpc<SUP>-3</SUP> is consistent with the dust-uncorrected UV-based SFRD. Future millimeter/submillimeter surveys can be used to detect a number of high-redshift line emitters, with which to study the star formation history in the early universe....

DOI： 10.1093/pasj/psx018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present spatially resolved ALMA observations of the CO J=3-2 emission line in two massive galaxies at z = 2.5 on the star-forming main sequence. Both galaxies have compact dusty star-forming cores with effective radii of {R}<SUB>{ { e</SUB> } }=1.3+/- 0.1 {kpc} and {R}<SUB>{ { e</SUB> } }=1.2+/- 0.1 {kpc} in the 870 μm continuum emission. The spatial extent of star-forming molecular gas is also compact with {R}<SUB>{ { e</SUB> } }=1.9+/- 0.4 {kpc} and {R}<SUB>{ { e</SUB> } }=2.3+/- 0.4 {kpc}, but more extended than the dust emission. Interpreting the observed position-velocity diagrams with dynamical models, we find the starburst cores to be rotation dominated with the ratio of the maximum rotation velocity to the local velocity dispersion of {v}<SUB>\max </SUB>/{σ }<SUB>0</SUB>={7.0}<SUB>-2.8</SUB><SUP>+2.5</SUP> ({v}<SUB>\max </SUB>={386}<SUB>-32</SUB><SUP>+36</SUP> km s<SUP>-1</SUP>) and {v}<SUB>\max </SUB>/{σ }<SUB>0</SUB>={4.1}<SUB>-1.5</SUB><SUP>+1.7</SUP> ({v}<SUB>\max </SUB>={391}<SUB>-41</SUB><SUP>+54</SUP> km s<SUP>-1</SUP>). Given that the descendants of these massive galaxies in the local universe are likely ellipticals with v/σ nearly an order of magnitude lower, the rapidly rotating galaxies would lose significant net angular momentum in the intervening time. The comparisons among dynamical, stellar, gas, and dust mass suggest that the starburst CO-to-H<SUB>2</SUB> conversion factor of {α }<SUB>{CO</SUB>}=0.8 {M}<SUB>☉ </SUB> (K km s<SUP>-1</SUP> pc<SUP>-2</SUP>)<SUP>-1</SUP> is appropriate in the spatially resolved cores. The dense cores are likely to be formed in extreme environments similar to the central regions of local ultraluminous infrared galaxies. Our work also demonstrates that a combination of medium-resolution CO and high-resolution dust continuum observations is a powerful tool for characterizing the dynamical state of molecular gas in distant galaxies....

DOI： 10.3847/2041-8213/aa7338

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arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We present 1{^''<SUB>.</SUB>}4 (98 pc) resolution ALMA observations of <SUP>13</SUP>CO(J = 1-0), C<SUP>18</SUP>O(J = 1-0), CS(J = 2-1), and CH<SUB>3</SUB>OH(J<SUB>K</SUB> = 2<SUB>K</SUB>-1<SUB>K</SUB>) molecular rotational lines in the central 1΄ (4.2 kpc) diameter region of NGC 1068 to study the physical and chemical properties of giant molecular clouds (GMCs) and to test whether these GMC-scale properties are linked to the larger-scale galactic environment. Using the derived <SUP>13</SUP>CO cube, we have identified 187 high-significance (&gt;8 σ) GMCs by employing the CLUMPFIND algorithm. The molecular gas masses of GMCs (M_^{13CO}), derived from the <SUP>13</SUP>CO data, range from 1.8 × 10<SUP>4</SUP> M<SUB>☉</SUB> to 4.2 × 10<SUP>7</SUP> M<SUB>☉</SUB>. A mass function of GMCs in NGC 1068 has been obtained for the first time at ∼100 pc resolution. We find the slope of the mass function γ = -1.25 ± 0.07 for a mass range of M_^{13CO} ≥ 10<SUP>5</SUP> M<SUB>☉</SUB>. This is shallower than the GMCs in the disk regions of the Milky Way, M 51, and NGC 300. Further, we find that the high mass cut-off of the GMC mass function occurs at M_^{13CO} ̃ 6 × 10<SUP>7</SUP> M<SUB>☉</SUB>, which is an order of magnitude larger than that in the nuclear bar region of M 51, indicating that the more massive clouds dominate the mass budget in NGC 1068. The observed C<SUP>18</SUP>O(J = 1-0)/<SUP>13</SUP>CO(J = 1-0) intensity ratios are found to be fairly uniform (0.27 ± 0.05) among the identified GMCs. In contrast, the CH<SUB>3</SUB>OH(J<SUB>K</SUB> = 2<SUB>K</SUB>-1<SUB>K</SUB>)/<SUP>13</SUP>CO(J = 1-0) ratios exhibit striking spatial variation across the disk, with the smallest values around the bar-end (&lt;0.03), and larger ratios along the spiral arms (∼0.1-0.2). We find that GMCs with detectable methanol emission tend to have systematically larger velocity widths than those without methanol emission, suggesting that (relatively weak) shocks are responsible for the enhancement of the CH<SUB>3</SUB>OH/<SUP>13</SUP>CO ratios of GMCs in the disk of NGC 1068. <P />...

DOI： 10.1093/pasj/psw122

Web of Science

Scopus

arXiv

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：OXFORD UNIV PRESS  

We report the results of optical-infrared follow-up observations of the gravitational wave (GW) event GW151226 detected by the Advanced LIGO in the framework of J-GEM (Japanese collaboration for Gravitational wave ElectroMagnetic follow-up). We performed wide-field optical imaging surveys with the Kiso Wide Field Camera (KWFC), Hyper Suprime-Cam (HSC), and MOA-cam3. The KWFC survey started at 2.26 d after the GW event and covered 778 deg<SUP>2</SUP> centered at the high Galactic region of the skymap of GW151226. We started the HSC follow-up observations from ̃12 d after the event and covered an area of 63.5 deg<SUP>2</SUP> of the highest probability region of the northern sky with limiting magnitudes of 24.6 and 23.8 for the i and z bands, respectively. MOA-cam3 covered 145 deg<SUP>2</SUP> of the skymap with the MOA-red filter ̃2.5 mon after the GW alert. The total area covered by the wide-field surveys was 986.5 deg<SUP>2</SUP>. The integrated detection probability for the observed area was ̃29%. We also performed galaxy-targeted observations with six optical and near-infrared telescopes from 1.61 d after the event. A total of 238 nearby (≤100 Mpc) galaxies were observed with a typical I band limiting magnitude of ̃19.5. We detected 13 supernova candidates with the KWFC survey, and 60 extragalactic transients with the HSC survey. Two thirds of the HSC transients were likely supernovae and the remaining one third were possible active galactic nuclei. With our observational campaign, we found no transients that are likely to be associated with GW151226. <P />...

DOI： 10.1093/pasj/psw113

Web of Science

Scopus

arXiv

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Language：English   Publishing type：Research paper (scientific journal)  

We present the detailed characterization of two extremely red submillimeter galaxies (SMGs), ASXDF1100.053.1 and 231.1, with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Jansky Very Large Array. These SMGs were originally selected using AzTEC at 1100 μm, and are observed by Herschel to be faint at 100-500 μm. Their (sub)millimeter colors are as red as—or redder—than known z ≳ 5 SMGs; indeed, ASXDF1100.053.1 is redder than HFLS 3, which lies at z = 6.3. They are also faint and red in the near-/mid-infrared: ̃1 μJy at IRAC 4.5 μm and &lt;0.2 μJy in the K <SUB>s</SUB> filter. These SMGs are also faint in the radio waveband, where F <SUB>6GHz</SUB> = 4.5 μJy for ASXDF1100.053.1 and F <SUB>1.4GHz</SUB> = 28 μJy for ASXDF1100.231.1, suggestive of z={6.5}<SUB>-1.1</SUB><SUP>+1.4</SUP> and z={4.1}<SUB>-0.7</SUB><SUP>+0.6</SUP> for ASXDF1100.053.1 and 231.1, respectively. ASXDF1100.231.1 has a flux excess in the 3.6 μm filter, probably due to Hα emission at z = 4-5. Derived properties of ASXDF1100.053.1 for z = 5.5-7.5 and 231.1 for z = 3.5-5.5 are as follows: their infrared luminosities are [6.5 - 7.4] × 10<SUP>12</SUP> and [4.2-4.5] × 10<SUP>12</SUP> L <SUB>☉</SUB> their stellar masses are [0.9-2] × 10<SUP>11</SUP> and [0.4-3] × 10<SUP>10</SUP> M <SUB>☉</SUB> their circularized half-light radii in the ALMA maps are ̃1 and ≲0.2 kpc (̃2-3 kpc for 90% of the total flux). Last, their surface infrared luminosity densities, Σ<SUB>IR</SUB>, are ̃1 × 10<SUP>12</SUP> and ≳1.5 × 10<SUP>13</SUP> L <SUB>☉</SUB> kpc<SUP>-2</SUP>, similar to values seen for local (U)LIRGs. These data suggest that ASXDF1100.053.1 and 231.1 are compact SMGs at z ≳ 4 and can plausibly evolve into z ≳ 3 compact quiescent galaxies....

DOI： 10.3847/1538-4357/835/2/286

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We present results from a deep 2'x3' (comoving scale of 3.7 Mpc x 5.5 Mpc at
z=3) survey at 1.1 mm taken with the Atacama Large Millimeter/submillimeter
Array (ALMA) in the SSA22 field. We observe the core region of a z = 3.09
protocluster, achieving a typical rms sensitivity of 60 micro-Jy/beam at a
spatial resolution of 0".7. We detect 18 robust ALMA sources at a
signal-to-noise ratio (SNR) > 5. Comparison between the ALMA map and a 1.1 mm
map taken with the AzTEC camera on the Atacama Submillimeter Telescope
Experiment (ASTE) indicates that three submillimeter sources discovered by the
AzTEC/ASTE survey are resolved into eight individual submillimeter galaxies
(SMGs) by ALMA. At least ten of our 18 ALMA SMGs have spectroscopic redshifts
of z = 3.09, placing them in the protocluster. This shows that a number of
dusty starburst galaxies are forming simultaneously in the core of the
protocluster. The nine brightest ALMA SMGs with SNR > 10 have a median
intrinsic angular size of 0".32+0".13-0".06 (2.4+1.0-0.4 physical kpc at z =
3.09), which is consistent with previous size measurements of SMGs in other
fields. As expected the source counts show a possible excess compared to the
counts in the general fields at S_1.1mm >= 1.0 mJy due to the protocluster. Our
contiguous mm mapping highlights the importance of large-scale structures on
the formation of dusty starburst galaxies.

DOI： 10.3847/1538-4357/835/1/98

Web of Science

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Astronomical Society  

We report the result from observations conducted with the Atacama Large
Millimeter/submillimeter Array (ALMA) to detect [CII] 158 um fine structure
line emission from galaxies embedded in one of the most spectacular Lyman-alpha
blobs (LABs) at z=3.1, SSA22-LAB1. Of three dusty star-forming galaxies
previously discovered by ALMA 860 um dust continuum survey toward SSA22-LAB1,
we detected the [CII] line from one, LAB1-ALMA3 at z=3.0993+/-0.0004. No line
emission was detected, associated with the other ALMA continuum sources or from
three rest-frame UV/optical selected z_spec~3.1 galaxies within the field of
view. For LAB1-ALMA3, we find relatively bright [CII] emission compared to the
infrared luminosity (L_[CII]/L_[CII]) and an extremely high [CII] 158 um and
[NII] 205 um emission line ratio (L_[CII]/L_[NII]>55). The relatively strong
[CII] emission may be caused by abundant photodissociation regions and
sub-solar metallicity, or by shock heating. The origin of the unusually strong
[CII] emission could be causally related to the location within the giant LAB,
although the relationship between extended Lyman-alpha emission and ISM
conditions of associated galaxies is yet to be understand.

DOI： 10.3847/2041-8213/834/2/L16

Web of Science

arXiv

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We present 0.″2-resolution Atacama Large Millimeter/submillimeter Array observations at 870 μm for 25 Hα-seleced star-forming galaxies around the main sequence at z = 2.2-2.5. We detect significant 870 μm continuum emission in 16 (64%) of these galaxies. The high-resolution maps reveal that the dust emission is mostly radiated from a single region close to the galaxy center. Exploiting the visibility data taken over a wide uv distance range, we measure the half-light radii of the rest-frame far-infrared emission for the best sample of 12 massive galaxies with log(M<SUB>*</SUB>/M<SUB>☉</SUB>) &gt; 11. We find nine galaxies to be associated with extremely compact dust emission with R<SUB>1/2,870 μm</SUB> &lt; 1.5 kpc, which is more than a factor of 2 smaller than their rest-optical sizes, &lt; {R}<SUB>1/2,1.6μ { { m</SUB> } }&gt; =3.2 {kpc}, and is comparable with optical sizes of massive quiescent galaxies at similar redshifts. As they have an exponential disk with Sérsic index of &lt; {n}<SUB>1.6μ { { m</SUB> } }&gt; =1.2 in the rest-optical, they are likely to be in the transition phase from extended disks to compact spheroids. Given their high star formation rate surface densities within the central 1 kpc of &lt; { { Σ } }{ { SFR } }<SUB>1{kpc</SUB>}&gt; =40 M<SUB>☉</SUB> yr<SUP>-1</SUP> kpc<SUP>-2</SUP>, the intense circumnuclear starbursts can rapidly build up a central bulge with ΣM<SUB>*,1 kpc</SUB> &gt; 10<SUP>10</SUP> M<SUB>☉</SUB> kpc<SUP>-2</SUP> in several hundred megayears, I.e., by z ̃ 2. Moreover, ionized gas kinematics reveal that they are rotation supported with an angular momentum as large as that of typical star-forming galaxies at z = 1-3. Our results suggest that bulges are commonly formed in extended rotating disks by internal processes, not involving major mergers....

DOI： 10.3847/1538-4357/834/2/135

Web of Science

arXiv

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