Faculty Profiles - INUTSUKA, Shu-ichiro

Papers - INUTSUKA, Shu-ichiro

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ALMA CO Observations of Supernova Remnant N63A in the Large Magellanic Cloud: Discovery of Dense Molecular Clouds Embedded within Shock-ionized and Photoionized Nebulae Open Access

Sano, H; Matsumura, H; Nagaya, T; Yamane, Y; Alsaberi, RZE; Filipovic, MD; Tachihara, K; Fujii, K; Tokuda, K; Tsuge, K; Yoshiike, S; Onishi, T; Kawamura, A; Minamidani, T; Mizuno, N; Yamamoto, H; Inutsuka, S; Inoue, T; Maxted, N; Rowell, G; Sasaki, M; Fukui, Y

ASTROPHYSICAL JOURNAL Vol. 873 ( 1 ) 2019.3

Publisher：Astrophysical Journal

We carried out new <sup>12</sup> CO(J = 1-0, 3-2) observations of a N63A supernova remnant (SNR) from the LMC using the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Submillimeter Telescope Experiment. We find three giant molecular clouds toward the northeast, east, and near the center of the SNR. Using the ALMA data, we spatially resolved clumpy molecular clouds embedded within the optical nebulae in both the shock-ionized and photoionized lobes discovered by previous H and [S ii] observations. The total mass of the molecular clouds is ∼800 M for the shock-ionized region and ∼1700 M for the photoionized region. Spatially resolved X-ray spectroscopy reveals that the absorbing column densities toward the molecular clouds are ∼(1.5-6.0) ? 10 <sup>21</sup> cm <sup>-2</sup> , which are ∼1.5-15 times less than the averaged interstellar proton column densities for each region. This means that the X-rays are produced not only behind the molecular clouds, but also in front of them. We conclude that the dense molecular clouds have been completely engulfed by the shock waves, but have still survived erosion owing to their high density and short interacting time. The X-ray spectrum toward the gas clumps is well explained by an absorbed power-law model or a high-temperature plasma model, in addition to thermal plasma components, implying that the shock-cloud interaction is efficiently working for both cases through the shock ionization and magnetic field amplification. If the hadronic gamma-ray is dominant in the GeV band, the total energy of the cosmic-ray protons is calculated to be ∼(0.3-1.4) ? 10 <sup>49</sup> erg, with an estimated interstellar proton density of ∼190 ? 90 cm <sup>-3</sup> , containing both the shock-ionized gas and neutral atomic hydrogen.

DOI： 10.3847/1538-4357/ab02fd

The Early Stage of Molecular Cloud Formation by Compression of Two-phase Atomic Gases Open Access

Iwasaki, K; Tomida, K; Inoue, T; Inutsuka, S

ASTROPHYSICAL JOURNAL Vol. 873 ( 1 ) 2019.3

Publisher：Astrophysical Journal

We investigate the formation of molecular clouds from atomic gas by using three-dimensional magnetohydrodynamic simulations, including non-equilibrium chemical reactions and heating/cooling processes. We consider super-Alfvénic head-on colliding flows of atomic gas possessing the two-phase structure that consists of H i clouds and surrounding warm diffuse gas. We examine how the formation of molecular clouds depends on the angle θ between the upstream flow and the mean magnetic field. We find that there is a critical angle θ <inf>cr</inf> above which the shock-amplified magnetic field controls the post-shock gas dynamics. If the atomic gas is compressed almost along the mean magnetic field (θ ≪ θ <inf>cr</inf> ), super-Alfvénic anisotropic turbulence is maintained by the accretion of the highly inhomogeneous upstream atomic gas. As a result, a greatly extended turbulence-dominated post-shock layer is generated. Around θ ∼ θ <inf>cr</inf> , the shock-amplified magnetic field weakens the post-shock turbulence, leading to a dense post-shock layer. For θ ≫ θ <inf>cr</inf> , the strong magnetic pressure suppresses the formation of cold dense clouds. Efficient molecular cloud formation is expected if θ is less than a few times θ <inf>cr</inf> . Developing an analytic model and performing a parameter survey, we obtain an analytic formula for the critical angle as a function of the mean density, collision speed, and field strength of the upstream atomic gas. The critical angle is found to be less than ∼15° as long as the field strength is larger than 1 μG, indicating that the probability of occurrence of compression with θ < θ <inf>cr</inf> is limited if shock waves come from various directions.

DOI： 10.3847/1538-4357/ab02ff

An Origin of Multiple Ring Structure and Hidden Planets in HL Tau: A Unified Picture by Secular Gravitational Instability (vol 152, 184, 2016) Open Access

Takahashi, SZ; Inutsuka, S

ASTRONOMICAL JOURNAL Vol. 157 ( 3 ) 2019.3

Publisher：Astronomical Journal

In our paper (Takahashi & Inutsuka 2016), there are typographical errors in Equations (13) and (17). The correct equations are σφ = -2πG/|κ| (σ∑/1 + kH + σ∑ <inf>d</inf>/1 + kH<inf>d</inf>), c<inf>d</inf><sup>2</sup> = 1 + 2(t<inf>stop</inf>ω)<sup>2</sup> + (5/4) (t<inf>stop</inf>ω)<sup>3</sup>/[1 + (t<inf>stop</inf>ω)<sup>2</sup>]<sup>2</sup> αc<inf>s</inf><sup>2</sup>. respectively. Since we used the correct equations in our calculations, these typographical errors do not change the dispersion relation in our original paper. Apart from the above typographical errors, we used an incorrect equation for the dust diffusion by the turbulence to calculate the dispersion relations. We underestimated (overestimated) the diffusion of dust particles with small (large) Stoke number. The secular GI is stabilized when we use the corrected equation with the exponential cutoff surface density model with the parameters given in the original paper, since the secular GI was marginally unstable with the parameters used in the original paper. Thus, we show the alternative results whose strength of the turbulence α are 2/3 times smaller than that used in the original paper. The fiducial value of α in the original paper is observationally suggested by Pinte et al. (2016). Since this α value is required from the observed sharp ring structure, this value should be regarded as an upper limit. Thus, the observation of the continuum emission of the disk around HL Tau can be explained by α = 2 × 10<sup>-4</sup>, with which the secular GI grows. Figures 1-5 are the same as Figures 1-5 in the original paper, but here we use α = 2 × 10<sup>-4</sup> instead of the value used in the original paper, α = 3 × 10<sup>-4</sup>. In Figure 3, the growth timescale in the upper right region is of the order of 10<inf>4</inf> yr, in which the Secular GI is stable in the original paper. In this region, the Stokes number becomes larger than unity. In the disk around HL Tau, however, it does not seem realized. We do not discuss the details of the instability in this region, which is beyond the scope of the paper. For Figures 6 and 7, we use α1 = 2 × 10<sup>-4</sup>(r/100 au)<sup>2</sup>, α2 = 2 × 10<sup>-4</sup>(r/100 au)<sup>3</sup>, instead of Equations (22) and (23) in the original paper. Since the growth timescales and the wavenumber in Figures 1-7 are similar to that in the original paper, all the conclusions in the original paper remain unchanged. We would like to thank Nicolai Skovby for pointing out our typographical errors and reproducing the dispersion relation, which drew our attention to our error. We also thank Ryosuke Tominaga for numerical comparison of the results in this erratum.

DOI： 10.3847/1538-3881/ab01d0

Two-component Secular Gravitational Instability in a Protoplanetary Disk: A Possible Mechanism for Creating Ring-like Structures (vol 794, 55, 2014) Open Access

Takahashi, SZ; Inutsuka, S

ASTROPHYSICAL JOURNAL Vol. 871 ( 1 ) 2019.1

Publisher：Astrophysical Journal

In our published article (Takahashi & Inutsuka 2014), there are typographical errors in Equations (26) and (29). The correct equations are (Formula Presented) respectively. Since we used the correct equations in our calculations, these typographical errors do not change the dispersion relation in our published article. We also found that the dispersion relation in Figure 2 is incorrect. The corrected Figure 2 is provided here. We used Equations (6), (9)-(12), (23), and (24) for the solid line in Figure 2, which means that we did not take into account the effect of the dust velocity dispersion and the disk thickness. When we use Equations (6), (9), (11), (23), (28), and (29) in the published article, the secular gravitational instability (GI) is stabilized with the parameters used in Figure 2. Therefore, we provide the alternative figure here (Figure 2). Figure 2 shows the dispersion relation with t <inf>stop</inf> ω = 0.02, Q = 3, ϵ = 0.1, and α = 10 <sup>-4</sup> . The solid line shows the dispersion relation calculated from Equations (6), (9), (11), (23), (28), and (29); and dashed line shows that calculated from Equations (6)-(12). Figure 2 shows that the growth rate of the instability decreases due to the turbulent viscosity, the dust velocity dispersion, and the disk thickness. All the discussions and conclusions in the published article remain unchanged. We would like to thank Nicolai Skovby for pointing out our typographical errors and reproducing the dispersion relation, which drew our attention to our error. We also thank Ryosuke Tominaga for numerical comparison of the results in this erratum. (Figure Presented).

DOI： 10.3847/1538-4357/aafc28

The Exchange of Mass and Angular Momentum in the Impact Event of Ice Giant Planets: Implications for the Origin of Uranus Open Access

Kurosaki, K; Inutsuka, S

ASTRONOMICAL JOURNAL Vol. 157 ( 1 ) 2019.1

Publisher：Astronomical Journal

Uranus has a tilted rotation axis, which is supposed to have been caused by a giant impact. In general, an impact event also changes the internal compositional distribution and drives mass ejection from the planet, which may provide the origin of satellites. Previous studies of the impact simulation of Uranus investigated the resultant angular momentum and the ejected mass distribution. However, the effect of changing the initial condition of the thermal and compositional structure is not studied. In this paper, we perform hydrodynamics simulations for the impact events of Uranus-size ice giants composed of a water core surrounded by a hydrogen envelope using two variant methods of the smoothed particle hydrodynamics. We find that the higher-entropy target loses its envelope more efficiently than the low-entropy target. However, the higher-entropy target gains more angular momentum than the lower-entropy target since the higher-entropy target has a more expanded envelope. We discuss the efficiency of angular momentum transport and the amount of the ejected mass and find a simple analytical model to roughly reproduce the outcomes of numerical simulations. We suggest the range of possible initial conditions for the giant impact on proto-Uranus that reproduces the present rotation tilt of Uranus and sufficiently provides the total angular momentum of the satellite system that can be created from the fragments from the giant impact.

DOI： 10.3847/1538-3881/aaf165

Radiation-hydrodynamic Simulations of Spherical Protostellar Collapse for Very Low-mass Objects Open Access

Stamer, T; Inutsuka, S

ASTROPHYSICAL JOURNAL Vol. 869 ( 2 ) 2018.12

Publisher：Astrophysical Journal

We perform radiation-hydrodynamical simulations of protostellar collapse in spherical symmetry, with a special focus on very low-mass objects, i.e., brown dwarfs and sub-brown dwarfs. The inclusion of a realistic equation of state, which includes the effect of hydrogen dissociation, allows for a modeling of the complete process from the beginning of the collapse until the formation of the protostar. We solve the frequency-dependent radiative transfer equation without any diffusion approximation, using realistic dust and gas opacities. Our results show that the properties of the protostar are essentially independent of the initial conditions, which had previously only been confirmed for higher mass ranges. For very low-mass initial conditions, however, we find that the first core phase of the collapse shows some significant differences in the time evolution, with the first core lifetime increasing dramatically because of the reduced accretion rate from the surrounding envelope. We consider the observational implications of this. We also investigate the opposite case of a collapse without any first core phase, which may occur for very unstable initial conditions. In the Appendix, we describe a severe numerical problem that causes an unphysical expansion after the formation of the protostar, which may affect other attempts at similar calculations of self-gravitational collapse. We explain the origin of the unphysical behavior and present a solution that can be used in similar investigations.

DOI： 10.3847/1538-4357/aaee81

Toward understanding the origin of asteroid geometries Variety in shapes produced by equal-mass impacts Open Access

Sugiura, K; Kobayashi, H; Inutsuka, S

ASTRONOMY & ASTROPHYSICS Vol. 620 2018.12

Publisher：Astronomy and Astrophysics

More than a half of the asteroids in the main belt have irregular shapes with ratios of the minor to major axis lengths of less than 0.6. One of the mechanisms that create such shapes is collisions between asteroids. The relationship between the shapes of collisional outcomes and impact conditions such as impact velocities may provide information on the collisional environments and its evolutionary stages when those asteroids are created. In this study, we perform numerical simulations of collisional destruction of asteroids with radii 50 km and subsequent gravitational reaccumulation using smoothed-particle hydrodynamics for elastic dynamics with self-gravity, a model of rock fractures, and a model of friction in completely damaged rock. We systematically vary the impact velocity from 50 to 400 m s <sup>-1</sup> and the impact angle from 5° to 45°. We investigate shapes of the largest remnants resulting from collisional simulations. As a result, various shapes (bilobed, spherical, flat, elongated, and hemispherical shapes) are formed through equal-mass and low-velocity (50-400 m s <sup>-1</sup> ) impacts. We clarify a range of the impact angle and velocity to form each shape. Our results indicate that irregular shapes, especially flat shapes, of asteroids with diameters larger than 80 km are likely to be formed through similar-mass and low-velocity impacts, which are likely to occur in the primordial environment prior to the formation of Jupiter.

DOI： 10.1051/0004-6361/201833227

Properties of an accretion disc with a power-law stress-pressure relationship Open Access

Shadmehri, M; Khajenabi, F; Dib, S; Inutsuka, S

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY Vol. 481 ( 4 ) page： 5170 - 5179 2018.12

Publisher：Monthly Notices of the Royal Astronomical Society

Recent numerical simulations of magnetized accretion discs show that the radial-azimuthal component of the stress tensor due to the magnetorotational instability is well represented by a power-law function of the gas pressure rather than a linear relation that has been used in most of the accretion disc studies. The exponent of this power-law function that depends on the net flux of the imposed magnetic field is reported in the range between zero and unity. However, the physical consequences of this power-law stress-pressure relation within the framework of the standard disc model have not been explored so far. In this study, the structure of an accretion disc with a power-law stress-pressure relation is studied using analytical solutions in the steady state and time-dependent cases. The derived solutions are applicable to different accreting systems, and as an illustrative example, we explore structure of protoplanetary discs using these solutions. We show that the slopes of the radial surface density and temperature distributions become steeper with decreasing the stress exponent. However, if the disc opacity is dominated by icy grains and value of the stress exponent is less than about 0.5, the surface density and temperature profiles become so steep that make them unreliable. We also obtain analytical solutions for the protoplanetary discs that are irradiated by the host star. Using these solutions, we find that the effect of the irradiation becomes more significant with decreasing the stress exponent.

DOI： 10.1093/mnras/sty2656

ALMA Reveals a Misaligned Inner Gas Disk inside the Large Cavity of a Transitional Disk Open Access

Mayama, S; Akiyama, E; Panic, O; Miley, J; Tsukagoshi, T; Muto, T; Dong, RB; de Leon, J; Mizuki, T; Oh, D; Hashimoto, J; Sai, J; Currie, T; Takami, M; Grady, CA; Hayashi, M; Tamura, M; Inutsuka, S

ASTROPHYSICAL JOURNAL LETTERS Vol. 868 ( 1 ) 2018.11

Publisher：Astrophysical Journal Letters

Pairs of azimuthal intensity decrements at near-symmetric locations have been seen in a number of protoplanetary disks. They are most commonly interpreted as the two shadows cast by a highly misaligned inner disk. Direct evidence of such an inner disk, however, remains largely illusive, except in rare cases. In 2012, a pair of such shadows were discovered in scattered-light observations of the near face-on disk around 2MASS J16042165-2130284, a transitional object with a cavity ∼60 au in radius. The star itself is a "dipper," with quasi-periodic dimming events on its light curve, commonly hypothesized as caused by extinctions by transiting dusty structures in the inner disk. Here, we report the detection of a gas disk inside the cavity using Atacama Large Millimeter/submillimeter Array (ALMA) observations with ∼0.″2 angular resolution. A twisted butterfly pattern is found in the moment 1 map of the CO (3-2) emission line toward the center, which is the key signature of a high misalignment between the inner and outer disks. In addition, the counterparts of the shadows are seen in both dust continuum emission and gas emission maps, consistent with these regions being cooler than their surroundings. Our findings strongly support the hypothesized misaligned inner disk origin of the shadows in the J1604-2130 disk. Finally, the inclination of the inner disk would be close to -45° in contrast with 45°; it is possible that its internal asymmetric structures cause the variations on the light curve of the host star.

DOI： 10.3847/2041-8213/aae88b

Does Misalignment between Magnetic Field and Angular Momentum Enhance or Suppress Circumstellar Disk Formation? Open Access

Tsukamoto, Y; Okuzumi, S; Iwasaki, K; Machida, MN; Inutsuka, S

ASTROPHYSICAL JOURNAL Vol. 868 ( 1 ) 2018.11

Publisher：Astrophysical Journal

The effect of misalignment between the magnetic field B and the angular momentum Jang of molecular cloud cores on the angular momentum evolution during the gravitational collapse is investigated by ideal and non-ideal MHD simulations. For the non-ideal effect, we consider the ohmic and ambipolar diffusion. Previous studies that considered the misalignment reported qualitatively contradicting results. Magnetic braking was reported as being either strengthened or weakened by misalignment in different studies. We conducted simulations of cloud core collapse by varying the stability parameter α (the ratio of the thermal to gravitational energy of the core) with and without including magnetic diffusion. The non-ideal MHD simulations show the central angular momentum of the core, with θ=0° (Jang B) being always greater than that with θ=90° (Jang B), independently of α, meaning that circumstellar disks form more easily in a core with θ=0°. The ideal MHD simulations, in contrast, show the central angular momentum of the core with θ=90° being greater than with θ=0° for small α and smaller for large α. Inspection of the angular momentum evolution of the fluid elements reveals three mechanisms contributing to the evolution of the angular momentum: (i) magnetic braking in the isothermal collapse phase, (ii) selective accretion of the rapidly (for θ = 90°) or slowly (for θ = 0°) rotating fluid elements to the central region, and (iii) magnetic braking in the first core and the disk. The difference between the ideal and non-ideal simulations arises from the different efficiencies of (iii).

DOI： 10.3847/1538-4357/aae4dc

Molecular filament formation and filament-cloud interaction: Hints from Nobeyama 45 m telescope observations Open Access

Arzoumanian, D; Shimajiri, Y; Inutsuka, S; Inoue, T; Tachihara, K

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN Vol. 70 ( 5 ) 2018.10

Publisher：Publications of the Astronomical Society of Japan

We present Nobeyama 45 m telescope C<sup>18</sup>O, <sup>13</sup>CO, and <sup>12</sup>CO(1-0) mapping observations towards an interstellar filament in the Taurus molecular cloud. We investigate the gas velocity structure along the filament and in its surrounding parent cloud. The filament is detected in the optically thin C<sup>18</sup>O emission as a single velocity component with a ∼1 pc long, ∼0.06 pc wide structure. The C<sup>18</sup>O emission traces dust column densities larger than ∼5 × 10<sup>21</sup> cm<sup>−2</sup>. The line-of-sight (LOS) velocity fluctuates along the filament crest with an average amplitude of ∼0.2 km s<sup>−1</sup>. The <sup>13</sup>CO and <sup>12</sup>CO integrated intensity maps show spatially extended emission around the elongated filament. We identify three extended structures with LOS velocities redshifted and blueshifted with respect to the average velocity of the filament identified in C<sup>18</sup>O. Based on combined analyses of velocity-integrated channel maps and intensity variations of the optically thick <sup>12</sup>CO spectra on and off the filament, we propose a three-dimensional structure of the cloud surrounding the filament. We further suggest a multi-interaction scenario where sheet-like extended structures interact, in space and time, with the filament and are responsible for its compression and/or disruption, playing an important role in the star formation history of the filament. We also identify, towards the same field, a very faint filament showing a velocity field compatible with the filament formation process proposed by Inoue et al. (2018, PASJ, 70, S53), where a filament is formed due to convergence of a flow of matter generated by the bending of the ambient magnetic field structure induced by an interstellar shock compression.

DOI： 10.1093/pasj/psy095

ALMA Observations of Supernova Remnant N49 in the LMC. I. Discovery of CO Clumps Associated with X-Ray and Radio Continuum Shells Open Access

Yamane, Y; Sano, H; van Loon, JT; Filipovic, MD; Fujii, K; Tokuda, K; Tsuge, K; Nagaya, T; Yoshiike, S; Grieve, K; Voisin, F; Rowell, G; Indebetouw, R; Lakicevic, M; Temim, T; Staveley-Smith, L; Rho, J; Long, KS; Park, S; Seok, J; Mizuno, N; Kawamura, A; Onishi, T; Inoue, T; Inutsuka, S; Tachihara, K; Fukui, Y

ASTROPHYSICAL JOURNAL Vol. 863 ( 1 ) 2018.8

Publisher：Astrophysical Journal

N49 (LHA 120-N49) is a bright X-ray supernova remnant (SNR) in the Large Magellanic Cloud. We present new <sup>12</sup>CO (J = 1-0, 3-2), H i, and 1.4 GHz radio continuum observations of the SNR N49 using Mopra, ASTE, ALMA, and ATCA. We have newly identified three H i clouds using ATCA with an angular resolution of ∼20″: one associated with the SNR and the others located in front of the SNR. Both the CO and H i clouds in the velocity range from 281 to 291 km s<sup>-1</sup> are spatially correlated with both the soft X-rays (0.2-1.2 keV) and the hard X-rays (2.0-7.0 keV) of N49 on a ∼10 pc scale. CO 3-2/1-0 intensity ratios indicate higher values of the CO cloud toward the SNR shell with an angular resolution of ∼45″, and thus a strong interaction was suggested. Using the ALMA, we have spatially resolved CO clumps embedded within or along the southeastern rim of N49 with an angular resolution of ∼3″. Three of the CO clumps are rim brightened on a 0.7-2 pc scale in both hard X-rays and the radio continuum: this provides further evidence for dynamical interactions between the CO clumps and the SNR shock wave. The enhancement of the radio synchrotron radiation can be understood in terms of magnetic field amplification around the CO clumps via a shock-cloud interaction. We also present a possible scenario in which the recombining plasma that dominates the hard X-rays from N49 was formed via thermal conduction between the SNR shock waves and the cold/dense molecular clumps.

DOI： 10.3847/1538-4357/aacfff

Warm CO Gas Generated by Possible Turbulent Shocks in a Low-mass Star-forming Dense Core in Taurus Open Access

Tokuda, K; Onishi, T; Saigo, K; Matsumoto, T; Inoue, T; Inutsuka, S; Fukui, Y; Machida, MN; Tomida, K; Hosokawa, T; Kawamura, A; Tachihara, K

ASTROPHYSICAL JOURNAL Vol. 862 ( 1 ) 2018.7

Publisher：Astrophysical Journal

We report ALMA Cycle 3 observations in CO isotopes toward a dense core, MC27/L1521F in Taurus, which is considered to be at an early stage of multiple star formation in a turbulent environment. Although most of the high-density parts of this core are considered to be as cold as ∼10 K, high-angular resolution (∼20 au) observations in <sup>12</sup>CO (J = 3-2) revealed complex warm (>15-60 K) filamentary/clumpy structures with the sizes from a few tens of astronomical units to ∼1000 au. The interferometric observations of <sup>13</sup>CO and C<sup>18</sup>O show that the densest part with arc-like morphologies associated with the previously identified protostar and condensations are slightly redshifted from the systemic velocity of the core. We suggest that the warm CO clouds may be consequences of shock heating induced by interactions among the different density/velocity components that originated from the turbulent motions in the core. However, such a small-scale and fast turbulent motion does not correspond to a simple extension of the line-width-size relation (i.e., Larson's law), and thus the actual origin remains to be studied. The high-angular resolution CO observations are expected to be essential in detecting small-scale turbulent motions in dense cores and to investigate protostar formation therein.

DOI： 10.3847/1538-4357/aac898

Magnetic Fields toward Ophiuchus-B Derived from SCUBA-2 Polarization Measurements Open Access

Soam, A; Pattle, K; Ward-Thompson, D; Lee, CW; Sadavoy, S; Koch, PM; Kim, G; Kwon, J; Kwon, W; Arzoumanian, D; Berry, D; Hoang, T; Tamura, M; Lee, SS; Liu, T; Kim, KT; Johnstone, D; Nakamura, F; Lyo, AR; Onaka, T; Kim, J; Furuya, RS; Hasegawa, T; Lai, SP; Bastien, P; Chung, EJ; Kim, S; Parsons, H; Rawlings, MG; Mairs, S; Graves, SF; Robitaille, JF; Liu, HL; Whitworth, AP; Eswaraiah, C; Rao, R; Yoo, H; Houde, M; Kang, JH; Doi, Y; Choi, M; Kang, M; Coudé, S; Li, HB; Matsumura, M; Matthews, BC; Pon, A; Di Francesco, J; Hayashi, SS; Kawabata, KS; Inutsuka, SI; Qiu, K; Franzmann, E; Friberg, P; Greaves, JS; Kirk, JM; Li, D; Shinnaga, H; van Loo, S; Aso, Y; Byun, DY; Chen, HR; Chen, MCY; Chen, WP; Ching, TC; Cho, J; Chrysostomou, A; Drabek-Maunder, E; Eyres, SPS; Fiege, J; Friesen, RK; Fuller, G; Gledhill, T; Griffin, MJ; Gu, QL; Hatchell, J; Holland, W; Inoue, T; Iwasaki, K; Jeong, IG; Kang, SJ; Kemper, F; Kim, KH; Kim, MR; Lacaille, KM; Lee, JE; Li, DL; Liu, JH; Liu, SY; Moriarty-Schieven, GH; Nakanishi, H; Ohashi, N; Peretto, N; Pyo, TS; Qian, L; Retter, B; Richer, J; Rigby, A; Savini, G; Scaife, AMM; Tang, YW; Tomisaka, K; Wang, HC; Wang, JW; Yen, HW; Yuan, JH; Zhang, CP; Zhang, GY; Zhou, JJ; Zhu, L; André, P; Dowell, D; Falle, S; Tsukamoto, Y; Kanamori, Y; Kataoka, A; Kobayashi, MIN; Nagata, T; Saito, H; Seta, M; Hwang, J; Han, I; Lee, H; Zenko, T

ASTROPHYSICAL JOURNAL Vol. 861 ( 1 ) 2018.7

Publisher：Astrophysical Journal

We present the results of dust emission polarization measurements of Ophiuchus-B (Oph-B) carried out using the Submillimetre Common-User Bolometer Array 2 (SCUBA-2) camera with its associated polarimeter (POL-2) on the James Clerk Maxwell Telescope in Hawaii. This work is part of the B-fields in Star-forming Region Observations survey initiated to understand the role of magnetic fields in star formation for nearby star-forming molecular clouds. We present a first look at the geometry and strength of magnetic fields in Oph-B. The field geometry is traced over ∼0.2 pc, with clear detection of both of the sub-clumps of Oph-B. The field pattern appears significantly disordered in sub-clump Oph-B1. The field geometry in Oph-B2 is more ordered, with a tendency to be along the major axis of the clump, parallel to the filamentary structure within which it lies. The degree of polarization decreases systematically toward the dense core material in the two sub-clumps. The field lines in the lower density material along the periphery are smoothly joined to the large-scale magnetic fields probed by NIR polarization observations. We estimated a magnetic field strength of 630 ± 410 μG in the Oph-B2 sub-clump using a Davis-Chandrasekhar-Fermi analysis. With this magnetic field strength, we find a mass-to-flux ratio λ = 1.6 ± 1.1, which suggests that the Oph-B2 clump is slightly magnetically supercritical.

DOI： 10.3847/1538-4357/aac4a6

The diverse lives of massive protoplanets in self-gravitating discs Open Access

Stamatellos, D; Inutsuka, S

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY Vol. 477 ( 3 ) page： 3110 - 3135 2018.7

Publisher：Monthly Notices of the Royal Astronomical Society

Gas giant planets may form early on during the evolution of protostellar discs, while these are relatively massive. We study how Jupiter-mass planet-seeds (termed protoplanets) evolve in massive, but gravitationally stable (Q ≳ 1.5), discs using radiative hydrodynamic simulations. We find that the protoplanet initially migrates inwards rapidly, until it opens up a gap in the disc. Thereafter, it either continues to migrate inwards on a much longer time-scale or starts migrating outwards. Outward migration occurs when the protoplanet resides within a gap with gravitationally unstable edges, as a high fraction of the accreted gas is high angular momentum gas from outside the protoplanet's orbit. The effect of radiative heating from the protoplanet is critical in determining the direction of the migration and the eccentricity of the protoplanet. Gap opening is facilitated by efficient cooling that may not be captured by the commonly used β-cooling approximation. The protoplanet initially accretes at a high rate (~10<sup>-3</sup> M<inf>J</inf> yr<sup>-1</sup>), and its accretion luminosity could be a few tenths of the host star's luminosity, making the protoplanet easily observable (albeit only for a short time). Due to the high gas accretion rate, the protoplanet generally grows above the deuterium-burning mass-limit. Protoplanet radiative feedback reduces its mass growth so that its final mass is near the brown dwarfplanet boundary. The fate of a young planet-seed is diverse and could vary from a gas giant planet on a circular orbit at a few au from the central star to a brown dwarf on an eccentric, wide orbit.

DOI： 10.1093/mnras/sty827

A Fast and Accurate Method of Radiation Hydrodynamics Calculation in Spherical Symmetry Open Access

Stamer, T; Inutsuka, S

ASTRONOMICAL JOURNAL Vol. 155 ( 6 ) 2018.6

Publisher：Astronomical Journal

We develop a new numerical scheme for solving the radiative transfer equation in a spherically symmetric system. This scheme does not rely on any kind of diffusion approximation, and it is accurate for optically thin, thick, and intermediate systems. In the limit of a homogeneously distributed extinction coefficient, our method is very accurate and exceptionally fast. We combine this fast method with a slower but more generally applicable method to describe realistic problems. We perform various test calculations, including a simplified protostellar collapse simulation. We also discuss possible future improvements.

DOI： 10.3847/1538-3881/aac023

A First Look at BISTRO Observations of the ρ Oph-A core Open Access

Kwon, J; Doi, Y; Tamura, M; Matsumura, M; Pattle, K; Berry, D; Sadavoy, S; Matthews, BC; Ward-Thompson, D; Hasegawa, T; Furuya, RS; Pon, A; Di Francesco, J; Arzoumanian, D; Hayashi, SS; Kawabata, KS; Onaka, T; Choi, M; Kang, M; Hoang, T; Lee, CW; Lee, SS; Liu, HL; Liu, T; Inutsuka, S; Eswaraiah, C; Bastien, P; Kwon, W; Lai, SP; Qiu, KP; Coudé, S; Franzmann, E; Friberg, P; Graves, SF; Greaves, JS; Houde, M; Johnstone, D; Kirk, JM; Koch, PM; Di Li, D; Parsons, H; Rao, R; Rawlings, MG; Shinnaga, H; van Loo, S; Aso, Y; Byun, DY; Chen, HR; Chen, MCY; Chen, WP; Ching, TC; Cho, J; Chrysostomou, A; Chung, EJ; Drabek-Maunder, E; Eyres, SPS; Fiege, J; Friesen, RK; Fuller, G; Gledhill, T; Griffin, MJ; Gu, Q; Hatchell, J; Holland, W; Inoue, T; Iwasaki, K; Jeong, IG; Kang, JH; Kang, SJ; Kemper, F; Kim, G; Kim, J; Kim, KT; Kim, KH; Kim, MR; Kim, S; Lacaille, KM; Lee, JE; Li, DL; Li, HB; Liu, JH; Liu, SY; Lyo, AR; Mairs, S; Moriarty-Schieven, GH; Nakamura, F; Nakanishi, H; Ohashi, N; Peretto, N; Pyo, TS; Qian, L; Retter, B; Richer, J; Rigby, A; Robitaille, JF; Savini, G; Scaife, AMM; Soam, A; Tang, YW; Tomisaka, K; Wang, HC; Wang, JW; Whitworth, AP; Yen, HW; Yoo, H; Yuan, JH; Zhang, CP; Zhang, GY; Zhou, JJ; Zhu, L; André, P; Dowell, CD; Falle, S; Tsukamoto, Y; Nakagawa, T; Kanamori, Y; Kataoka, A; Kobayashi, MIN; Nagata, T; Saito, H; Seta, M; Zenko, T

ASTROPHYSICAL JOURNAL Vol. 859 ( 1 ) 2018.5

Publisher：Astrophysical Journal

We present 850 μm imaging polarimetry data of the ρ Oph-A core taken with the Submillimeter Common-User Bolometer Array-2 (SCUBA-2) and its polarimeter (POL-2) as part of our ongoing survey project, -fields In STar forming RegiOns (BISTRO). The polarization vectors are used to identify the orientation of the magnetic field projected on the plane of the sky at a resolution of 0.01 pc. We identify 10 subregions with distinct polarization fractions and angles in the 0.2 pc ρ Oph-A core; some of them can be part of a coherent magnetic field structure in the ρ Oph region. The results are consistent with previous observations of the brightest regions of ρ Oph-A, where the degrees of polarization are at a level of a few percent, but our data reveal for the first time the magnetic field structures in the fainter regions surrounding the core where the degree of polarization is much higher (>5%). A comparison with previous near-infrared polarimetric data shows that there are several magnetic field components that are consistent at near-infrared and submillimeter wavelengths. Using the Davis-Chandrasekhar-Fermi method, we also derive magnetic field strengths in several subcore regions, which range from approximately 0.2 to 5 mG. We also find a correlation between the magnetic field orientations projected on the sky and the core centroid velocity components.

DOI： 10.3847/1538-4357/aabd82

Differences in the Gas and Dust Distribution in the Transitional Disk of a Sun-like Young Star, PDS 70 Open Access

Long, ZC; Akiyama, E; Sitko, M; Fernandes, RB; Assani, K; Grady, CA; Cure, M; Danchi, WC; Dong, RB; Fukagawa, M; Hasegawa, Y; Hashimoto, J; Henning, T; Inutsuka, SI; Kraus, S; Kwon, J; Lisse, CM; Liu, HB; Mayama, S; Muto, T; Nakagawa, T; Takami, M; Tamura, M; Currie, T; Wisniewski, JP; Yang, Y

ASTROPHYSICAL JOURNAL Vol. 858 ( 2 ) 2018.5

Publisher：Astrophysical Journal

We present ALMA 0.87 mm continuum, HCO<sup>+</sup> J = 4-3 emission line, and CO J = 3-2 emission line data of the disk of material around the young, Sun-like star PDS 70. These data reveal the existence of a possible two-component transitional disk system with a radial dust gap of 0.″42 ±0.″05, an azimuthal gap in the HCO<sup>+</sup> J = 4-3 moment zero map, as well as two bridge-like features in the gas data. Interestingly these features in the gas disk have no analog in the dust disk making them of particular interest. We modeled the dust disk using the Monte Carlo radiative transfer code HOCHUNK3D using a two-disk component. We find that there is a radial gap that extends from 15 to 60 au in all grain sizes, which differs from previous work.

DOI： 10.3847/1538-4357/aaba7c

Star formation induced by cloud-cloud collisions and galactic giant molecular cloud evolution Open Access

Kobayashi, MIN; Kobayashi, H; Inutsuka, S; Fukui, Y

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN Vol. 70 ( Special Issue 2 ) 2018.5

Publisher：Publications of the Astronomical Society of Japan

Recent millimeter/submillimeter observations towards nearby galaxies have started to map the whole disk and to identify giant molecular clouds (GMCs) even in the regions between galactic spiral structures. Observed variations of GMC mass functions in different galactic environments indicates that massive GMCs preferentially reside along galactic spiral structures whereas inter-arm regions have many small GMCs. Based on the phase transition dynamics from magnetized warm neutral medium to molecular clouds, Kobayashi et al. (2017, ApJ, 836, 175) proposes a semi-analytical evolutionary description for GMC mass functions including a cloud-cloud collision (CCC) process. Their results show that CCC is less dominant in shaping the mass function of GMCs than the accretion of dense HI gas driven by the propagation of supersonic shock waves. However, their formulation does not take into account the possible enhancement of star formation by CCC. Millimeter/submillimeter observations within the Milky Way indicate the importance of CCC in the formation of star clusters and massive stars. In this article, we reformulate the time-evolution equation largelymodified from Kobayashi et al. (2017, ApJ, 836, 175) so that we additionally compute star formation subsequently taking place in CCC clouds. Our results suggest that, although CCC events between smaller clouds are more frequent than the ones between massive GMCs, CCC-driven star formation is mostly driven by massive GMCs ≲ 10<sup>5.5</sup> M<inf>⊙</inf> (where M<inf>⊙</inf> is the solar mass). The resultant cumulative CCC-driven star formation may amount to a few 10 percent of the total star formation in the Milky Way and nearby galaxies.

DOI： 10.1093/pasj/psy018

The formation of massive molecular filaments and massive stars triggered by a magnetohydrodynamic shock wave

Inoue, T; Hennebelle, P; Fukui, Y; Matsumoto, T; Iwasaki, K; Inutsuka, S

PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN Vol. 70 ( Special Issue 2 ) 2018.5

Publisher：Publications of the Astronomical Society of Japan

Recent observations suggest an that intensive molecular cloud collision can trigger massive star/cluster formation. The most important physical process caused by the collision is a shock compression. In this paper, the influence of a shock wave on the evolution of a molecular cloud is studied numerically by using isothermal magnetohydrodynamics simulations with the effect of self-gravity. Adaptive mesh refinement and sink particle techniques are used to follow the long-time evolution of the shocked cloud. We find that the shock compression of a turbulent inhomogeneous molecular cloud creates massive filaments, which lie perpendicularly to the background magnetic field, as we have pointed out in a previous paper. The massive filament shows global collapse along the filament, which feeds a sink particle located at the collapse center. We observe a high accretion rate M<inf>acc</inf> > 10<sup>-4</sup> M<inf>⊙</inf> yr<sup>-1</sup> that is high enough to allow the formation of even O-type stars. The most massive sink particle achieves M > 50M<inf>⊙</inf> in a fewtimes 10<sup>5</sup> yr after the onset of the filament collapse.

DOI： 10.1093/pasj/psx089

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