Faculty Profiles - INUTSUKA, Shu-ichiro

Fragmenting Filaments and Evolving Cores-Insights from Dust Polarization Study of a Filament in Northern Orion B Open Access

Mallick, KK; Arzoumanian, D; Takahashi, S; Furuya, RS; Misugi, Y; Shimajiri, Y; Pattle, K; Inutsuka, S

ASTROPHYSICAL JOURNAL Vol. 998 ( 1 ) 2026.2

Modeling of Collisional Outcomes Based on Impact Simulations of Mars-sized Bodies Open Access

Kobayashi, H; Tanaka, H; Hasegawa, Y; Inutsuka, SI

ASTROPHYSICAL JOURNAL Vol. 998 ( 1 ) 2026.2

Linear analyses of thermal instability in stratified medium Open Access

Seno, I; Inutsuka, SI; Shimoda, J

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY Vol. 546 ( 1 ) 2026.2

Publisher：Monthly Notices of the Royal Astronomical Society

Thermal instability in the circumgalactic medium (CGM) can be responsible for the existence of cold clouds (e.g. high-velocity clouds) embedded in a hot diffuse medium (e.g. X-ray emitting gas). While many previous studies have analysed thermal instability in uniform medium, the instability mechanism in gravitationally stratified medium like CGM has not been fully analysed. This study investigates how gravity affects the behaviour of thermal instability through linear perturbation analyses. We find that in stratified medium, thermal instability can drive overstable modes, a behaviour distinctly different from the monotonic growth of thermal instability in a uniform medium. Furthermore, we find that the combination of buoyancy and thermal instability drives other two unstable modes. Applying our results to a simplified model of the CGM, we estimate the gas accretion rate from the CGM to the Galactic disc and the typical size of high-velocity cloud driven by thermal instability to be a few M yr −1 . This gas accretion rate is comparable to the observed star formation rate, and hence, the mass in the Galactic disc can be maintained. Our results provide a theoretical framework for understanding the formation of multi-phase gas, particularly in the CGM.

DOI： 10.1093/mnras/staf2268

Special relativistic smoothed particle hydrodynamics based on Riemann solver

Kitajima, K; Inutsuka, SI; Seno, I

JOURNAL OF COMPUTATIONAL PHYSICS Vol. 545 2026.1

The Dynamical Interaction between Low-mass Planets and Dust Coagulation Open Access

Hou, Q; Yu, C; Inutsuka, S

ASTROPHYSICAL JOURNAL LETTERS Vol. 995 ( 1 ) 2025.12

Publisher：Astrophysical Journal Letters

We investigate the impact of a low-mass planet on dust coagulation, and its consequent feedback on planetary migration, using a linear analysis of the coupled dust–gas hydrodynamic equations. Dust coagulation is incorporated via a single-size approximation. In the co-orbital region of the planet, we find that the growth of dust size is significantly suppressed by planet-induced coagulation modes (CMs). These effects are less pronounced with smaller stopping times, stronger gaseous turbulence, or imperfect sticking. Regarding planetary migration, we find that CMs make outward migration require τ ≳ 0.3 (τ is dimensionless stopping time) with typical turbulent strength and dust coagulation efficiency. We demonstrate that the torque variations are reasonable and arise from phase shifts between the density and stopping time perturbations in the coagulation modes.

DOI： 10.3847/2041-8213/ae2331

Evolution of magnetized hub-filament systems Comparing the observed properties of W3(OH), W3 Main, and S 106 Open Access

Kumar, MSN; Arzoumanian, D; Inutsuka, S; Furuya, R; Bhadari, NK

ASTRONOMY & ASTROPHYSICS Vol. 703 2025.11

Publisher：Astronomy and Astrophysics

Context. Hub-filament systems (HFSs) span a broad range of star-forming gas densities and are widely recognized as the progenitors of open star clusters. They serve as ideal targets for investigating the physical properties of star-forming gas and observing how dense gas is removed during the assembly of star clusters. Aims. In this study, we explore the characteristics of three cluster-forming HFSs – W3(OH), W3 Main, and S 106 – that represent evolutionary stages from early to evolved, with a particular focus on the structure of their magnetic fields (B-field) and filament line-mass distributions. The goal is to identify indicators of the evolution of the HFSs, in particular, their hubs, as star formation proceeds. Methods. Our analysis combines observations of dense star-forming gas and young stellar populations. We present new JCMT/POL-2 observations of 850 µm dust polarized emission to probe the dense gas and magnetic field structures. Additionally, we utilized archival infrared and radio data from WIRCAM, WFCAM, Spitzer, Herschel, and the VLA to identify markers of star formation. We derived radial column density profiles centred in the hubs and used them to define distinct filament and hub regions. We analysed istograms of line mass (M<inf>line</inf>), polarization intensity (PI), polarization fraction (PF), and the relative orientation between the magnetic field and the filaments. Results. Each hub contains two adjacent nodes or peaks of star formation, with one peak consistently more evolved than the other. The radial intensity profiles for all three targets fit well with two distinct power laws, -s between 0.6–0.8 pc; these define the semimajor axes of the hub, which approximates an elliptical shape. The power-law indices for the hub regions (0.6–0.8 pc) are −2.1, −1.7, and −0.9, and for the filament regions (>0.8 pc) they are −2.9, −4.2, and −11.7, corresponding to W3(OH), W3 Main, and S 106, respectively. These power-law slopes indicate different dynamical behaviours (where ≤−2 suggests global collapse), which is important to understand HFSs evolution. The hubs contain the highest line masses across all targets. In the earliest stage W3(OH), the filament line-mass function (FLMF) smoothly includes both the hub and filament regions in a Salpeter-like slope. In the evolved S 106, the hub FLMF slope is −0.85 and the filament region FLMF slope is −1.4. The plane-of-sky (POS) magnetic field structures display two notable features: (a) at low densities, B-field lines are misaligned with filaments but gradually align with them as density increases towards the hub; (b) B-field lines trace the walls of bipolar cavities formed by massive outflows from stars in the hub. PF and PI contour maps show disc and bipolar outflow-like patterns centred on the most luminous sources. Additionally, we identify a foreground mini-spiral HFS in W3 Main, previously recognized as the coldest clump in the region. Conclusions. As HFSs evolve, discernible changes can be found in the FLMF, PF, and B-field-Filament angles, especially inside the hub, which is also found to increase in size. Massive bipolar outflows and radiation bubbles significantly reshape POS magnetic fields, aligning them along cavity walls and shells, adding to the well-documented rearrangements around HII region cavities. We notice there is an intriguing similarity between hub sizes and young cluster radii. The presence of ‘double-node’ star formation within hubs – characterized by systematic evolutionary differences – appears to be a common feature of HFSs. We present evidence for their widespread occurrence in several well-studied, nearby star-forming clouds.

DOI： 10.1051/0004-6361/202554901

Growth of Massive Molecular Cloud Filament by Accretion Flows. II. New Mechanism to Support a Supercritical Filament Against Radial Collapse

Abe, D; Inoue, T; Inutsuka, SI; Arzoumanian, D

ASTROPHYSICAL JOURNAL Vol. 987 ( 2 ) 2025.7

Publisher：Astrophysical Journal

Observations indicate that dense molecular filamentary clouds are sites of star formation. The filament width determines the most unstable scale for self-gravitational fragmentation and influences the stellar mass. Therefore, constraining the evolution of filaments and the origin of their properties is important for understanding star formation. Although some observations show a universal width of 0.1 pc, many theoretical studies predict the contraction of thermally supercritical filaments (>17 M<inf>⊙ </inf>pc−1) due to radial collapse. Through nonideal magnetohydrodynamics simulations with ambipolar diffusion, we explore the formation and evolution of filaments via slow-shock instability at the front of accretion flows. We reveal that ambipolar diffusion allows the gas in the filament to flow across the magnetic fields around the shock front, forming dense blobs behind the concave points of the shock front. The blobs transfer momentum that drives internal turbulence. We name this mechanism “the STORM”(Slow-shock-mediated Turbulent flOw Reinforced by Magnetic diffusion). The persistence and efficiency of the turbulence inside the filament are driven by the magnetic field and the ambipolar diffusion effect, respectively. The STORM mechanism sustains the width even when the filament reaches very large line masses (∼100 M<inf>⊙ </inf>pc−1).

DOI： 10.3847/1538-4357/add529

The JCMT BISTRO Survey: Unveiling the Magnetic Fields around Galactic Center

Yang, MZ; Lai, SP; Karoly, J; Pattle, K; Lu, X; Eden, D; Lin, SJ; Poidevin, F; Sharma, E; Hwang, J; Fanciullo, L; Tahani, M; Koch, PM; Inutsuka, S; Le Gouellec, VJM; Duan, HY; Wang, JW; Fuller, G; Furuya, RS; Gu, QL; Hasegawa, T; Li, GX; Liu, JH; Akshaya, MS; Najimudeen, B; Tram, L; Ward-Thompson, D; Arzoumanian, D; Di Francesco, J; Doi, Y; Hoang, T; Kang, JH; Kwon, J; Kwon, W; Lee, CW; Liu, T; Onaka, T; Sadavoy, S; Tamura, M; Bastien, P; Berry, D; Coudé, S; Qiu, KP

ASTROPHYSICAL JOURNAL Vol. 983 ( 2 ) 2025.4

Publisher：Astrophysical Journal

We acquired 450 and 850 μm dust continuum polarization observations toward the inner region of the Central Molecular Zone (CMZ) as part of the B-Fields In Star-forming Region Observations survey using the POL-2 polarimeter on the James Clerk Maxwell Telescope. These observations encompassed three dense structures: the 20 km s−1 cloud (20MC), 50 km s−1 cloud (50MC), and circumnuclear disk (CND). Our aim is to investigate the magnetic field morphology and strength in the inner region of the CMZ using polarized dust continuum and the Davis-Chandrasekhar-Fermi method. The magnetic field morphology is highly ordered in all three dense regions. The plane-of-sky magnetic field strengths are ∼1 mG for the 20MC and the 50MC, and ∼2 mG for the CND. We compare the energy contributions of turbulence, gravity, and thermal motion with that of the magnetic field using the plasma β, mass-to-flux ratio, and Alfvén Mach number. The outcomes reveal the magnetic field stands out as the predominant factor within the inner region of the CMZ. The dominance of the magnetic field may explain the low star-forming rate in the CMZ. We further investigate the dust grain alignment efficiency by exploring the relationship between polarization fraction and total intensity. The results suggest that dust grains are well aligned with the magnetic fields.

DOI： 10.3847/1538-4357/adbe34

Analytical and numerical linear analyses of convection revisited

Seno, I; Inutsuka, S

PHYSICS OF FLUIDS Vol. 37 ( 4 ) 2025.4

Publisher：Physics of Fluids

We conduct linear analyses of convection in domains larger than the temperature scale height. We employ both analytical and numerical methods in these analyses. In the case excluding all dissipation, the typical timescale of convection is determined by the free fall time over the temperature scale height. We quantitatively show the condition for the Boussinesq and Wentzel-Kramers-Brillouin (WKB) approximations to be applicable. We provide a reassessment of the critical Rayleigh number, a key indicator of convection, and show that WKB approximation tends to underestimate the critical Rayleigh number, particularly when the temperature scale height is comparable to or smaller than the domain height. We show clear explanation why both thermal conduction and viscosity are required for stabilizing a negative entropy gradient medium.

DOI： 10.1063/5.0263373

ALMA observations of massive clouds in the central molecular zone: slim filaments tracing parsec-scale shocks Reviewed International coauthorship International journal

Yang, K; Lu, X; Zhang, YC; Liu, XC; Ginsburg, A; Liu, HB; Cheng, Y; Feng, SY; Liu, T; Zhang, QZ; Mills, EAC; Walker, DL; Inutsuka, SI; Battersby, C; Longmore, SN; Tang, XD; Kauffmann, J; Gu, QL; Li, SH; Luo, QY; Kruijssen, JMD; Pillai, T; Qiao, HH; Qiu, KP; Shen, ZQ

ASTRONOMY & ASTROPHYSICS Vol. 694 2025.2

Language：English Publishing type：Research paper (scientific journal) Publisher：Astronomy and Astrophysics

The central molecular zone (CMZ) of our Galaxy exhibits widespread emission from SiO and various complex organic molecules (COMs), yet the exact origin of such emission is uncertain. Here we report the discovery of a unique class of long (>0.5 pc) and narrow (<0.03 pc) filaments in the emission of SiO 5-4 and eight additional molecular lines, including several COMs, in our ALMA 1.3 mm spectral line observations toward two massive molecular clouds in the CMZ, which we name as slim filaments. However, these filaments are not detected in the 1.3 mm continuum at the 5σ level. Their line-of-sight velocities are coherent and inconsistent with being outflows. The column densities and relative abundances of the detected molecules are statistically similar to those in protostellar outflows but different from those in dense cores within the same clouds. Turbulent pressure in these filaments dominates over self gravity and leads to hydrostatic inequilibrium, indicating that they are a different class of objects than the dense gas filaments in dynamical equilibrium ubiquitously found in nearby molecular clouds. We argue that these newly detected slim filaments are associated with parsec-scale shocks, likely arising from dynamic interactions between shock waves and molecular clouds. The dissipation of the slim filaments may replenish SiO and COMs in the interstellar medium and lead to their widespread emission in the CMZ.

DOI： 10.1051/0004-6361/202453191

A Tale of Three: Magnetic Fields along the Orion Integral-shaped Filament as Revealed by the JCMT BISTRO Survey Reviewed International coauthorship International journal

Astrophysical Journal Letters Vol. 977 ( 2 ) 2024.12

The JCMT BISTRO Survey: The Magnetic Fields of the IC 348 Star-forming Region Reviewed International coauthorship International journal

Choi, Y; Kwon, W; Pattle, K; Arzoumanian, D; Bourke, TL; Hoang, T; Hwang, J; Koch, PM; Sadavoy, S; Bastien, P; Furuya, R; Lai, SP; Qiu, KP; Ward-Thompson, D; Berry, D; Byun, DY; Chen, HRV; Chen, WP; Chen, M; Chen, ZW; Ching, TC; Cho, J; Choi, M; Choi, Y; Coudé, S; Chrysostomou, A; Chung, EJ; Dai, S; Debattista, V; Di Francesco, J; Diep, PN; Doi, Y; Duan, HY; Duan, Y; Eswaraiah, C; Fanciullo, L; Fiege, J; Fissel, LM; Franzmann, E; Friberg, P; Friesen, R; Fuller, G; Gledhill, T; Graves, S; Greaves, J; Griffin, M; Gu, QL; Han, I; Hasegawa, T; Houde, M; Hull, CLH; Inoue, T; Inutsuka, S; Iwasaki, K; Jeong, IG; Johnstone, D; Karoly, J; Könyves, V; Kang, JH; Kang, MJ; Kataoka, A; Kawabata, K; Kemper, F; Kim, J; Kim, S; Kim, G; Kim, KH; Kim, MR; Kim, KT; Kim, H; Kirchschlager, F; Kirk, J; Kobayashi, MIN; Kusune, T; Kwon, J; Lacaille, K; Law, CY; Lee, CW; Lee, H; Lee, CF; Lee, JE; Lee, SS; Li, DL; Li, D; Li, GX; Li, HB; Lin, SJ; Liu, HL; Liu, T; Liu, SY; Liu, JH; Longmore, S; Lu, X; Lyo, AR; Mairs, S; Matsumura, M; Matthews, B; Moriarty-Schieven, G; Nagata, T; Nakamura, F; Nakanishi, H; Ngoc, NB; Ohashi, N; Onaka, T; Park, G; Parsons, H; Peretto, N; Priestley, F; Pyo, TS; Qian, L; Rao, R; Rawlings, J; Rawlings, M; Retter, B; Richer, J; Rigby, A; Saito, H; Savini, G; Seta, M; Sharma, E; Shimajiri, Y; Shinnaga, H; Soam, A; Tahani, M; Tamura, M; Tang, YW; Tang, XD; Tomisaka, K; Tram, LN; Tsukamoto, Y; Viti, S; Wang, HC; Wang, JW; Whitworth, A; Wu, JT; Xie, JJ; Yang, MZ; Yen, HW; Yoo, H; Yuan, JH; Yun, HS; Zenko, T; Zhang, GY; Zhang, YP; Zhang, CP; Zhou, JJ; Zhu, L; de Looze, I; André, P; Dowell, CD; Eden, D; Eyres, S; Falle, S; Le Gouellec, VJM; Poidevin, F; van Loo, S

ASTROPHYSICAL JOURNAL Vol. 977 ( 1 ) 2024.12

Language：English Publishing type：Research paper (scientific journal) Publisher：Astrophysical Journal

We present 850 μm polarization observations of the IC 348 star-forming region in the Perseus molecular cloud as part of the B-fields In STar-forming Region Observation survey. We study the magnetic properties of two cores (HH 211 MMS and IC 348 MMS) and a filamentary structure of IC 348. We find that the overall field tends to be more perpendicular than parallel to the filamentary structure of the region. The polarization fraction decreases with intensity, and we estimate the trend by power law and the mean of the Rice distribution fittings. The power indices for the cores are much smaller than 1, indicative of possible grain growth to micron size in the cores. We also measure the magnetic field strengths of the two cores and the filamentary area separately by applying the Davis-Chandrasekhar-Fermi method and its alternative version for compressed medium. The estimated mass-to-flux ratios are 0.45-2.20 and 0.63-2.76 for HH 211 MMS and IC 348 MMS, respectively, while the ratios for the filament are 0.33-1.50. This result may suggest that the transition from subcritical to supercritical conditions occurs at the core scale (∼0.05 pc) in the region. In addition, we study the energy balance of the cores and find that the relative strength of turbulence to the magnetic field tends to be stronger for IC 348 MMS than for HH 211 MMS. The result could potentially explain the different configurations inside the two cores: a single protostellar system in HH 211 MMS and multiple protostars in IC 348 MMS.

DOI： 10.3847/1538-4357/ad88ed