O. R. Jadhav

Intense radiation from high-mass stars is expected to significantly affect dust grain alignment and evolution through radiative torques (RATs). We investigate this effect in a massive star-forming region, NGC 6334I, using 1.2 mm dust continuum polarization observations from the Atacama Large Millimeter/submillimeter Array. The polarization fraction spans from ≲1% to ∼10% and decreases with increasing column density, remaining below 2% in dense cores despite high temperatures (∼100 K), where efficient grain alignment by RATs is expected. We investigate how grain alignment, grain growth, grain disruption, B -field tangling, and local physical conditions affect the polarization properties of MM1, MM2, MM3, and their surroundings. Polarization-angle dispersion shows that B -field tangling contributes to depolarization at moderate densities but cannot fully explain the lowest-polarization fractions. Using RAT-based grain alignment and polarization modeling, we find that reduced alignment efficiency and high optical depth reproduce the low polarization in the densest regions. MM2 shows evidence of grain growth, with maximum grain sizes a max ∼ 0.35 – 1.0 μ m, while MM1 exhibits smaller values of ∼0.35–0.50 μ m. Accounting for optical depth increases the inferred grain sizes in MM1 to ∼1.0–2.0 μ m. Analytical estimates of RAT disruption from the intense outburst suggest that micron-sized grains in high-temperature, moderate-density regions can fragment into submicron grains. Alternatively, high optical depth may also explain the low polarization in the densest regions even in the presence of micron-sized grains. Incorporating the B -field inclination effect indicates a transition from predominantly plane-of-sky fields at low densities to more line-of-sight-aligned configurations at high densities.

We present a multiscale kinematic study of the hub–filament system in Mon R2 using James Clerk Maxwell Telescope (JCMT) ¹³ CO(3–2) and Atacama Large Millimeter/submillimeter Array (ALMA) C ¹⁸ O(1–0) observations to investigate how molecular gas converges toward the central hub and connects across cloud-to-core scales. The ¹³ CO data reveal several velocity-coherent filaments with diverse position angles converging toward the central region hosting massive stars and stellar clusters, where distinct velocity components become spatially superposed. Two dominant velocity regimes at ∼8.8–10.2 and ∼10.4–11.8 km s ⁻¹ are identified, with their velocity separation decreasing toward the central hub. The position–position–velocity (PPV) and longitude–velocity maps of the ¹³ CO emission exhibit a butterfly/X-shaped morphology, consistent with converging motions. A phenomenological rotating-and-infalling envelope model reproduces the longitude–velocity morphology, indicating that rotation and infall may contribute to the observed kinematics, although the model does not uniquely identify the underlying mechanism. At higher resolution, the ALMA C ¹⁸ O observations resolve the molecular gas into multiple velocity-coherent filaments spanning ∼8–13 km s ⁻¹ , with distinct kinematic domains at ∼9–10.5, 10.5–11.5, and 12–13 km s ⁻¹ converging toward the hub. The ALMA and JCMT position–velocity (PV) diagrams show consistent velocity structures across their respective spatial scales, with the ALMA-resolved features embedded within the broader molecular gas velocity field traced by JCMT, demonstrating a multiscale kinematic connection. These results support a hierarchical picture in which converging flows and filamentary accretion contribute to hub growth and ongoing star formation in Mon R2, while other dynamical processes may also contribute to the observed kinematics.

Our understanding of magnetic fields (B-fields) in massive star formation remains incomplete. Linear polarized emission from magnetically aligned dust grains provides a good way to map the morphology of the B-field on the plane of the sky. Here, we present the 1.2 mm full polarization observation of W33 A, a massive star-forming region at 2.4 kpc, obtained with the Atacama Large Mil-limeter/Submillimeter Array (ALMA) to achieve an angular resolution of ∼0″.3 (∼730 au). W33 A is resolved into 20 dense cores and nine filaments. It reveals various B-field structures, including two perpendicular large-scale components oriented northwest–southeast (NW–SE) and northeast–southwest (NE–SW), as well as two local distinct features toward the millimeter peaks MM1 and MM2. The NW–SE component could be shaped by a molecular outflow. The NE–SW one is remarkably coherent along the main filamentary structures (F1, F-Main, Tail), all with trans-Alfvénic turbulence. In F-Main, the line mass exceeds the turbulent critical limits, so magnetic support is required to prevent radial collapse and suppress local fragmentation. In F1 and Tail, turbulence is sufficient to support gravity, although B-fields can potentially provide additional support. Toward MM1, the fields follow a spiral-like, infalling streamer traced by CH ₃ CN; the inferred trans-Alfvénic turbulence in the accreting material indicates magnetic damping of turbulence and a magnetically regulated, laminar accretion flow that continues to feed the core. Toward MM2, the field exhibits an hourglass geometry described by parabolic curves. Two independent methods yield a consistently strong field strength of ∼8.1 ± 1.9 mG. The virial analysis shows that the B-field can add 25% (75% from turbulence) support against gravity but is not by itself sufficient to halt collapse. Our study shows that within one protocluster, B-fields can both help stabilize gas filament against local fragmentation to facilitate mass accretion and delay gravitational collapse. The distinct evolutionary stages of MM1 and MM2 highlight the dynamic importance of B-fields in massive star formation.

To investigate the role of magnetic fields toward the G35N and G35S subregions in the G35.20–0.74 star-forming complex, we utilized multiwavelength polarimetric observations from the SOFIA/HAWC+ at 154 μ m and Atacama Cosmology Telescope (ACT) at 220 GHz/1.3 mm. The ACT 220 GHz polarization data (resolution ∼1 ′ ) show an hourglass-shaped plane-of-sky magnetic field morphologies toward both the subregions, though with distinct symmetry axes. SOFIA/HAWC+ 154 μ m data (resolution ∼13 . ″ 6) confirm an hourglass morphology in G35N, whereas G35S displays a different magnetic field configuration compared to the ACT observations. An hourglass morphology identified at clump scales (∼a parsec) toward G35N is consistent with the previously reported B -field morphology at core scales (∼0.05 pc), supporting the scenario of a magnetically regulated collapse. Using the SOFIA/HAWC+ data, we estimate magnetic field strengths of ∼600 ± 200 μ G in G35N and ∼850 ± 310 μ G in G35S. Energy balance analysis suggests that gravity and magnetic fields contribute comparably in G35N, while in G35S the gas dynamics are dominated by magnetic field, followed by gravity and turbulence. The higher field strength in G35S likely results from compression by the expanding H ii region, highlighting the impact of stellar feedback. The derived magnetic field strengths and corresponding magnetic energies should be treated as upper limits due to unresolved beam-scale correlations and the limited fitting range of the polarization angle structure function. Overall, our results show that magnetic fields decisively regulate star formation, with G35N shaped by magnetically controlled collapse and G35S being strongly influenced by stellar feedback.

We present the SOFIA/HAWC+ 214 μm polarimetric observations toward the infrared dark cloud G351.77-0.53 (hereafter G351), complemented by existing multi-wavelength data sets. Infrared excess from the embedded sources indicate ongoing star formation activity in the cloud. The G351 cloud hosts two prominent star-forming clumps, i.e., c1 and c2. The plane-of-the-sky magnetic field lines from Planck observations are predominantly oriented perpendicular to the filament’s major axis. Magnetic field orientations from SOFIA/HAWC+ 214 μm observations reveal distinct hourglass-shaped field configuration toward c1, while the field lines remain perpendicular to the rest of the filament. Using the Davis-Chandrasekhar-Fermi method, we estimate a mean plane-of-the-sky magnetic field strength of ~147 ± 60 μG in the G351 filament, with values reaching ~0.8 mG toward c1. The mass-to-flux ratio analysis indicates that the filament is magnetically transcritical, where the gravitational and magnetic field energies are comparable. The hourglass-shaped magnetic field observed toward c1 could result from magnetically regulated gravitational collapse, the alignment of converging sub-filaments with the magnetic field, or a combination of both processes. The energy budget analysis further indicates that magnetic fields play an important role in governing the cloud’s gas dynamics, followed by contributions from turbulence and gravity.

We report the discovery of 45 compact hub-filament systems (HFSs; median size ∼2.4 pc) in infrared-dark clouds (IRDCs) in the W33 complex, located at the junction of the Scutum and Norma spiral arms. Using Spitzer 8 and 24 µ m, and unWISE 12 μ m images, HFSs are identified as regions where three or more filaments converge onto a central hub, appearing as absorption features toward IRDCs. In each IRDC, HFSs mainly lie at the intersections of elongated substructures, associated with groups of protostars and lacking radio continuum emission. Minimum Spanning Tree (MST) analysis shows that protostars are closely associated with the HFSs, with protostellar core separations of ≤0.7 pc, indicating strong clustering within fragmented structures. The HFSs form two main groupings spanning 10–15 pc, with member separations of 1–3.3 pc. Around 65% are tightly clustered (5 cm ⁻³ ), whereas the core spacing is smaller than the Jeans length, suggesting that thermal fragmentation may influence core formation but alone cannot explain the larger-scale protostellar distribution. All these findings together support a picture in which fragments of clouds/filaments form clumps hosting compact HFSs that facilitate efficient and clustered star formation, often yielding massive stars.

We investigate the magnetic field orientation and strength in the massive star-forming region G35.20-0.74N (G35), using polarized dust emission data obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) as part of the Magnetic fields in Massive star-forming Regions (MagMaR) survey. The G35 region shows a filamentary structure (a length of ∼0.1 pc) with six bright cores located along the filament’s long axis. Magnetic field strengths across the G35 region range from 0.2 to 4.4 mG with a mean value of 0.8 ± 0.4 mG. The mass-to-flux ratio ( λ ) varies from 0.1 to 6.0, the critical value. The highest values are found locally around cores, whereas the remains of the filament are subcritical. A H ¹³ CO ⁺ (3–2) velocity gradient of 29 km s ⁻¹ pc ⁻¹ is evident along the filament’s long axis, aligned with the magnetic field direction. At larger scales (∼0.1 pc), the magnetic field lines appear roughly perpendicular to the filament’s long axis, in contrast to the smaller-scale structure (∼0.003 pc) traced by ALMA. The magnetic field lines could be dragged along the filament as a result of the gas motion induced by the gravitational potential of the filament. Six cores in the filament have similar spacings between 0.02 and 0.04 pc. The initial filament fragmentation could have produced a core spacing of 0.06 pc, following filament fragmentation theory, and the current core spacing is the result of cores comoving with the gas along the filament. This core migration could occur in a few 10 ⁴ yr, consistent with high-mass star formation timescales.

We present a multiwavelength study of the filamentary cloud G47 (d ∼ 4.44 kpc), which hosts the mid-infrared bubbles N98, B1, and B2. The SMGPS 1.3 GHz continuum map detects ionized emission toward all the bubbles, marking the first detection of ionized emission toward the B2 bubble. Analysis of the unWISE 12.0 μm image, the Spitzer 8.0 μm image, and the Herschel column density and temperature maps reveals two previously unreported hub–filament system candidates associated with the H ii regions B2 and N98, which are powered by massive OB stars. This indirectly favors the applicability of a global nonisotropic collapse scenario for massive star formation in N98 and B2. The position–position–velocity diagram of FUGIN ¹³CO (1–0) shows significant velocity variations from 61 to 53 km s⁻¹ toward areas between B2 and N98, where the magnetic field morphology exhibits significant curvature and high velocity dispersion (i.e., 2.3–3.1 km s⁻¹) is observed. This may be explained by the expansion of the H ii regions B2 and N98. The energy budget of the cloud, estimated using SOFIA/HAWC+ and molecular line data, suggests that the magnetic field dominates over turbulence and gravity in G47. Furthermore, the radial column density and velocity profiles of G47 display signatures of converging flows in a sheet-like structure. The relative orientations between the magnetic field and local gravity suggest that G47 may undergo gravitational contraction along the magnetic field lines once it becomes magnetically supercritical.