arXiv subjects

Hauyu Baobab Liu

Publications and source records attributed to Hauyu Baobab Liu.

At least 19 recordsLinked to original sources

arXiv2026

The 200-300 GHz Survey for 18 Class II Disks in the Ophiuchus Star-Forming Complex

We measured the 198-310 GHz flux densities of 18 Class II protoplanetary disks in the Ophiuchus star-forming complex using the Submillimeter Array (SMA). The $\sim$200-300 GHz spectral indices ($α_{200-300}$) of these disks are $2.3^{+0.2}_{-0.5}$. In this observed frequency range, emission properties of the Ophiuchus disks are very similar to the 48 spatially compact Class II disks in the Taurus-Auriga region observed in a previous SMA survey. Combining the Ophiuchus and Taurus-Auriga samples, the Pearson correlation coefficient between $α_{200-300}$ and the flux density at 250 GHz ($F_{250\,\mathrm{GHz}}$) is 0.27 ($p=0.02$). We do not find a convincing correlation between $α_{200-300}$ and the $R_{95\%}$ radius of the disks. Our interpretation for the $α_{200-300}$ values being close to 2 in the spatially compact disks is that at $\gtrsim 200$ GHz frequencies, the continuum emission in these disks is dominated by optically thick dust thermal emission, independent of $F_{250\,\mathrm{GHz}}$ and $R_{95\%}$. As a result, the (sub)millimeter luminosity and the apparent disk size are positively correlated, which has been found in numerous resolved emission surveys of Class II disks. In young clusters with ages of $\sim$1-2 Myr, Class II disks with smaller radii or lower (sub)millimeter luminosities are not necessarily those in which the dust mass budget has been consumed or dispersed.

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arXiv2026

Low Star Formation Efficiency in M31: Evidence for a Deficit of Bound Gas

The Andromeda galaxy (M31) exhibits a systematically low star formation efficiency (SFE) compared to other star-forming galaxies. Star formation is thought to be regulated by the mass of gravitationally bound gas. To investigate whether the low SFE in M31 originates from a scarcity of such bound gas, we analyze the dynamical state of its giant molecular cloud (GMC) population by estimating their virial parameters ($α_{\rm vir}$). Using a JCMT-SCUBA2 850 micron dust-continuum GMC catalog as the parent sample, we combine it with IRAM 30 m CO(1-0) data to define a working sample of 173 GMCs and derive their kinematic properties. Most analyzed GMCs exhibit high $α_{\rm vir}$, indicating that they are predominantly gravitationally unbound at the approximately 86 pc resolution of our observations. While no statistically significant global correlation is found between SFE and $α_{\rm vir}$ for the full cloud sample, the upper quantiles of the SFE distribution show progressively stronger negative trends with increasing $α_{\rm vir}$. This upper-tail trend may arise from the combined effects of the virial parameter limiting the upper range of SFE values accessible to the GMC population and feedback-driven disruption reducing the number of high-SFE, high-$α_{\rm vir}$ CO-bright clouds in the observed sample. The substantial scatter in the SFE-$α_{\rm vir}$ plane likely reflects the diverse evolutionary stages of GMCs, the temporal mismatch between gas and star formation tracers, and the limitations of a cloud-averaged virial parameter as a tracer of internal dynamical structure, making a simple one-to-one correspondence between $α_{\rm vir}$ and instantaneous SFE difficult to recover for individual GMCs.

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arXiv2026

Multi-wavelength Constraints on Dust Dynamics and Size Evolution in Protoplanetary Disk Rings. II. Observational Implications

Spatially resolved dust rings in protoplanetary disks are widely used to infer disk and dust physics from multi-wavelength continuum observations. Their interpretation, however, often neglects grain growth and the evolution of the size distribution, limiting the connection between observed ring profiles and dust-evolution parameters. Building on a physical dust-ring model that includes coagulation and fragmentation, we develop a Bayesian inference framework that jointly incorporates radiative transfer and finite angular resolution. When applied to two rings in HD 163296 and two in LkCa 15, our framework yields gas-dependent estimates of the key dust-evolution parameters such as turbulence strength $α$ and the fragmentation velocity $v_{\rm frag}$ in a self-consistent way. Most rings admit both a low-$α$, low-$v_{\rm frag}$ branch with small grains, and a higher-$α$, higher-$v_{\rm frag}$ branch with larger grains. Typical low-$α$ branches have $α\sim10^{-5}$--$10^{-4}$ and fragmentation velocities of order cm s$^{-1}$ level, whereas the higher-$α$ branches reach $α\sim10^{-3}$--$10^{-2}$ and fragmentation velocities of a few to $20$ m s$^{-1}$. The observed broad and wavelength-dependent profiles near the ring peaks can be reproduced by intrinsically narrow dust rings. This new framework offers a more direct route from multi-wavelength continuum data to the microphysics of dust growth and trapping---a connection that can be robustly tested with future high-resolution observations at longer wavelengths.

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arXiv2026

ALMA Polarization Study of the Magnetic Fields in Two Massive Clumps in the 20 km s$^{-1}$ Cloud of the Central Molecular Zone

We present the Atacama Large Millimeter/submillimeter Array (ALMA) observations of linearly polarized 870 $μ$m continuum emission at a resolution of $\sim$0.2$^{\prime\prime}$ (2000 au) toward the two massive clumps, Clump 1 and Clump 4, in the 20 km s$^{-1}$ cloud. The derived magnetic field strengths for both clumps range from $\sim$0.3 to 3.1 mG using the Angular Dispersion Function (ADF) method. The magnetic field orientations across multiple scales suggests that the magnetic field dominates at the cloud scale, whereas gravity likely governs the structures at the core (0.01$-$0.1 pc) and condensation ($\le$ 0.01 pc) scales. Furthermore, the study on the angular difference between the orientations of the local gravity gradient and the magnetic field suggests that the gravity predominantly governs the dynamics in the diffuse regions, while both gravity and star formation feedback become increasingly significant within the dense regions. The ratio of the magnetic field tension force $F_\mathrm{B}$ to the gravitational force $F_\mathrm{G}$ suggests that the magnetic field may provide some support against gravity, but it is insufficient to prevent gas from infalling toward the dense cores.

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arXiv2026

Dust characterization of the HD 163296 disk with high-resolution multi-wavelength ALMA observations

Context. Planets form through the growth and accumulation of dust grains in protoplanetary disks. Characterizing dust properties such as size, surface density, and temperature is key to understanding planet formation. Aims. We characterize the dust properties of the protoplanetary disk around HD 163296 by performing spectral energy distribution (SED) fitting of multi-wavelength high-resolution observations. Methods. We present new high-resolution ALMA Band 9 (0.45 mm) observations, which are sensitive to the temperature. We performed SED fitting at a common resolution of 0.066 arcsec using these new Band 9 observations along with archival ALMA Band 3, 4, 6, and 7 observations. We compared the fitted results with VLA observations and explored multiple dust models with different optical constants and porosities. Results. The Band 9 image shows the central disk, two rings at 0.67 and 1.00 arcsec, and outer extended emission previously seen at other wavelengths. At higher frequencies, the rings appear wider, the gaps appear shallower, and the extended emission appears brighter, which can be explained by optical-depth effects and/or size segregation. We characterized the dust properties, including temperature, surface density, and dust size, for each dust model. However, the inferred dust properties are dependent on the dust model, and the ALMA data alone do not allow us to determine which dust model is preferred. We identified the DSHARP Zubko (porous) model as the preferred model based on VLA profiles and physical and observational constraints. The outer ring temperature is lower than predicted by a passively irradiated disk model, suggesting shadowing by the inner ring. Although the surface density and dust size depend on the dust model, the preferred model indicates that the central disk, both rings, and the extended disk each contain more than a few Earth masses of dust.

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arXiv2026

Dense Cores in the Vicinity of an HII Region

Massive stars strongly influence their surroundings through radiative and mechanical feedback, but its effects on dense gas structures at sub-pc scales remain poorly constrained. We investigate how feedback from a newly formed massive star affects dense cores in the filamentary molecular cloud IRAS 18530+0215. We analyze ALMA Band 6 observations of 1.3 mm dust continuum and DCN, N$_2$D$^+$, and $^{13}$CS line emission, together with VLA K-band continuum and NH$_3$ observations. Dense cores are identified with astrodendro, and their temperatures, masses, velocity dispersions, and virial parameters are derived. The dynamical state of the ultra-compact H II region is examined through energy and pressure estimates. The H II region has a radius of $\sim$0.1 pc and an expansion velocity of $\sim$2.5 km s$^{-1}$, corresponding to a shell dynamical age of $\sim$0.06 Myr. DCN and $^{13}$CS cores are concentrated near the H II region, whereas N$_2$D$^+$ cores preferentially lie farther away. Core temperatures and velocity dispersions decrease with projected distance from the H II region. Virial parameters increase within the inner $\sim$0.3 pc but decline sharply beyond this scale, while core masses show no significant trend with distance. Strong star formation signatures are found at $\sim$0.2 pc, whereas more distant regions still host quiescent, cold dense cores. The compact H II region appears trapped or choked within $\sim$0.1 pc, while its feedback extends to at least $\sim$0.3 pc. Within this region, feedback enhances core velocity dispersions, gas temperatures, and virial parameters, with no evidence that it promotes the formation of more massive dense cores.

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arXiv2026

MIAO-ALMA: Shocks and Protostellar Outflows in 70 $μ$m-dark clumps with $L/M$ $<$ 1 $L_{\odot}$/$M_{\odot}$

To investigate the initial conditions of high-mass star-forming regions, we use SiO (2-1) emission to trace early shock-related kinematics toward sixteen 70 $μ$m-dark and massive clumps with luminosity-to-mass ratios ($L/M$) $< 1\,L_{\odot}/M_{\odot}$, as part of the Multiwavelength Line-Imaging Survey of the 70 $μ$m-dark and bright clouds (MIAO) project. Using ALMA observations at a spatial resolution of $\sim$0.06 pc and a velocity resolution of 0.21 km s$^{-1}$, we identify a total of thirty-seven outflows with a variety of morphologies. Outflow parameters were derived by integrating the HCO$^+$ (1-0) line wings, excluding the quiescent dense core component traced by H$^{13}$CO$^+$ (1-0). We find that outflow masses and velocities show moderate positive correlations with the masses of their driving cores. Owing to the high sensitivity of our observations, which yield longer projected outflow lengths compared to previous studies, the derived outflow dynamical ages span $\sim10^{3}$-$10^{5}$ yr. We detect six narrow-linewidth (0.6-1.4 km s$^{-1}$) and three broad ($>$ 2 km s$^{-1}$) SiO (2-1) features not associated with outflows driven by clearly identified protostars. Lacking coincident 3 mm dust continuum cores, their origins may be young outflows from undetected low-mass protostars, dissipating shocks, cloud-cloud collisions, or projection effects when the outflows lie close to the plane of the sky. The detection of these shocks and outflows in such extremely young environments demonstrates that protostellar activity has already begun.

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arXiv2026

ALOHA IRDCs Molecular Line Follow-up: I. Gas properties and kinematics

Infrared Dark Clouds are ideal sites for investigating the initial conditions of massive star and cluster formation. The A Lei Of the Habitat and Assembly of Infrared Dark Clouds (ALOHA IRDCs), a James Clerk Maxwell Telescope (JCMT) Large Program, has mapped nearby IRDCs with SCUBA-2. Complementary molecular line observations are needed to characterise the physical, kinematic, and chemical properties of the dense gas. We aim to determine the thermal, kinematic, and chemical properties of clumps identified in the ALOHA IRDCs, and to assess their evolutionary status and level of star-forming activity. We performed single-pointing K-band and W-band observations towards 56 ALOHA IRDCs clumps using the Effelsberg 100-m and Yebes 40-m telescopes, respectively. We derived NH3 kinetic temperatures using the hyperfine group ratio (HFGR) method and identified infall and shock signatures from HCO+, H13CO+, SiO, and HNCO profiles. Water masers and NH2D emission were used as complementary tracers of chemical evolution and star formation. The clumps exhibit kinetic temperatures of 15-29 K. We detect NH2D emission towards 18 sources, with NH2D centroid velocities consistent with NH3, indicating both species trace the same dense gas component. More than half of the clumps display blue-asymmetric HCO+ profiles, identifying them as infall candidates. Water masers are detected in 22 sources, with prominent velocity ranges and variability. Broad SiO emission (>~20 km/s) indicates strong shocks, while narrower extents (<~6km/s) likely trace large-scale interactions or low-velocity shocks. The widespread infall signatures, shock tracers, masers, and NH2D emission suggest that relatively quiescent, chemically young material can coexist with dynamically active gas affected by early protostellar feedback, providing insight into the coupled physical and chemical evolution of massive IRDC clumps.

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arXiv2026

Trace the Self-Gravitating Gas Using CO Isotopologues

Recent studies have shown that the star formation rate (SFR) correlates tightly and linearly with the mass of gravitationally bound gas, which can be delineated from the power-law tail of the column-density probability distribution function ($N$-PDF) derived from dust emission observations. This relationship holds across four orders of magnitude within the Milky Way--spanning low-mass to high-mass star-forming regions and encompassing the extreme environment of the Central Molecular Zone. Building on this framework, we present a new approach for estimating the mass of gravitationally bound gas in molecular clouds using multi-line CO isotopologue observations. Our sample includes 16 molecular clouds with robust detections in $^{12}$CO, $^{13}$CO, and C$^{18}$O $J$ = 1-0, spanning both massive inner Galaxy clouds and nearby star-forming regions. We find that the $N$-PDFs derived from combined CO isotopologue data recover the characteristic log-normal plus power-law profiles seen in dust-based studies. The mass and spatial distribution of the self-gravitating structures estimated from both dust-based and CO-based methods agree well throughout the sample. This indicates that the CO isotopologue combination can robustly trace the self-gravitating component via the $N$-PDF method and provides a reliable, scalable, and velocity-resolved alternative to dust emission for identifying the star-forming gas in molecular clouds.

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arXiv2026

Nascent Embedded-protostar Survey in Taurus (NEST) II: Measuring Dust Mass, Disk Size, and Gas Mass

Envelope-embedded protostellar disks represent the earliest stage of protoplanetary disk evolution, but their masses and sizes are difficult to measure because disk emission is entangled with the envelope. We analyze 26 protostellar disk systems in Taurus using ALMA Band 7 (345 GHz; ~0.3'') and VLA Ka-band (33 GHz; ~0.2'') continuum observations, together with molecular-line data to constrain disk gas masses. At 345 GHz, the median flux density, dust mass, and radius are 71 mJy, 5.5 M_Mearth, and 28 AU, with 68% ranges of 54-107 mJy, 3.9-9.4 M_Mearth, and 25-39 AU. At 33 GHz, the corresponding medians are 0.43 mJy, 39 M_Mearth, and 32 AU, with ranges of 0.41-0.80 mJy, 34-52 M_Mearth, and 29-33 AU. Taurus Class I disks are fainter and less massive than those in Orion, comparable to Perseus Class I disks but fainter than Perseus Class 0 disks, and brighter and more massive than those in Ophiuchus. Within Taurus, Class 0/I disks are brighter than Class II disks at both frequencies, although their inferred dust masses are comparable at 345 GHz and slightly higher at 33 GHz. Radiative-transfer modeling of CO isotopologue emission yields a median gas mass of 6.7 x 10^-4 M_Msun. The resulting CO-inferred gas-to-dust ratios span a broad range, with a mean of 147 +/- 75, a median of 26, and a 16th-84th percentile range of 8-147. This distribution overlaps the Taurus Class II population at the low end and ISM-like or higher values, including the AGE-PRO Ophiuchus Class 0/I population, at the high end.

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arXiv2026

SMA 200-400 GHz Survey for 10 faint Class II Disks in the Taurus Molecular Cloud

We have performed Submillimeter Array (SMA) observations of 198.0-407.5 GHz broadband spectra of 10 Class II protoplanetary disks in the Taurus-Auriga region. The 337 GHz flux densities ($F_{\rm 337 GHz}$) of these objects are in the range of 8.2-34 mJy. The median and standard deviation of the 198-358 GHz spectral indices ($α_{198-358}$) of these 10 Class II disks are 1.9 and 0.3, respectively. Compared to the recent, similar SMA survey on another 47 Class II disks that are brighter at (sub)millimeter bands ($F_{\rm 337 GHz}\sim$20-730 mJy), there is no evidence that these newly observed 10 fainter Class II disks have systematically different $α_{198-358}$ values. At $>$230 GHz frequencies, the optical depths of these 10 fainter Class II disks may be as high as those of the brighter sources, which may be $\gtrsim$5. In addition, the low ($<$2.0) values of $α_{198-358}$ in some faint objects may be explained by the effect of dust self-scattering, with maximum dust grain size ($a_{\rm max}$) $\sim$ 100 $μ$m, or by contamination by free-free emission.

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arXiv2026

Spatially resolved thermal dust emission in the L1157 outflow reveals grain-driven molecular enrichment

Protostellar outflow shocks reshape local dust properties and molecular chemistry. The L1157 outflow is an archetypal chemically rich shocked region, but the thermal dust associated with its successive shocks has remained unresolved because molecular-line contamination obscures the broadband continuum. We obtained new James Clerk Maxwell Telescope (825--906 $μ$m) spectral-line observations and Submillimeter Array (1.1--1.4 mm) continuum observations toward L1157 B0-B1-B2, probing spatial scales from 0.4 pc to 1200 au. After removing molecular-line contamination on a pixel-by-pixel basis, we derived the dust temperature, column density, and dust opacity index from continuum data spanning 70 $μ$m to 1.3 mm. The line-corrected continuum maps reveal the dust distribution across successive shocks. The dust opacity index ($β\approx1.8$--2.3) indicates that grains have not grown to millimeter sizes throughout the shocked regions. Combined with previous $\rm NH_3$ observations, we find that the dust emission resolves into compact clumps along the precessing jet, whereas gaseous $\rm NH_3$ peaks at the shock fronts, reaching abundances of $\sim10^{-5}$ relative to $\rm H_2$, even where the 0.85 and 1.3 mm dust emission is detected at only 3--5$σ$. Our newly developed physicochemical shock model shows that $\rm NH_3$ forms predominantly on grain surfaces and is released by shock-induced sputtering, with the highest abundances occurring where post-shock re-adsorption remains inefficient. These results establish spatially resolved dust continuum imaging as a direct observational probe of grain evolution and provide new observational constraints on dust-gas interactions in protostellar shocks.

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arXiv2026

A Hybrid Origin for the Multiple Ring-Gap Structures in the Large Protoplanetary Disk V1094 Sco: A Low-Mass Planet and Secular Gravitational Instability

High spatial resolution observations reveal that some protoplanetary disks host multiple ring-gap pairs at large stellocentric radii, yet their physical origin remains unsettled. We present a multi-wavelength analysis of the V1094~Sco disk using Atacama Large Millimeter/submillimeter Array Band~6 continuum and $^{12}$CO and $^{13}$CO $J=2-1$ emission, together with a Very Large Telescope/SPHERE near-infrared scattered light image. The continuum image shows four narrow dust ring-gap pairs extending to exceptionally large radii ($r \sim 380$ au), while the CO isotopologues trace a spatially extended gas disk ($r \sim 760$ au) in Keplerian rotation. From the dust ring widths, we place conservative upper limits on the turbulent viscosity parameter, $α\lesssim 10^{-3}$ and potentially $\lesssim 10^{-4}$, implying weak turbulence. The ensemble of gap widths and depths is inconsistent with a simple one-planet-per-gap interpretation. At $r \simeq 100$~au, a double gap and its scattered light counterpart are consistent with multi-gap excitation by a single low-mass companion of $(55 \pm 35)\,M_{\oplus}$. At $r \simeq 170$-$230$~au, the outer ring system shows regular spacing and no clear scattered light counterpart, indicating mechanisms that operate primarily at the disk midplane. These outer rings are quantitatively compatible with secular gravitational instability. V1094~Sco therefore supports a hybrid pathway in which weak turbulence in an extended disk allows secular gravitational instability to assemble long-lived midplane dust concentrations that can cradle planet formation beyond $\sim100$~au, alongside planet-driven substructures at intermediate radii.

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arXiv2026

A JWST, ALMA and VLA survey of the Ophiuchus-A star-forming region: Unveiling hidden dust mass and connecting infrared outflows to their radio origins

We present an infrared, millimetre, and radio survey of 20 Class 0-III young stellar objects in the Ophiuchus A L1688 star-forming cluster, combining high-resolution (7-25 au) VLA and JWST observations with archival ALMA data. We implement physically motivated models to derive dust and ionised gas properties, spectral behaviour and their relative contributions through the millimetre-centimetre radio spectral energy distribution. Our models reveal circumstellar dust disks that are, on average, tens to hundreds of times more massive than millimetre-only estimates (subject to uncertainties arising from the choice of dust opacity) and contain millimetre-sized grains even at the Class 0 stage. Owing to the VLA's high resolution we are able to connect outflows to their origins, detecting protostellar jet emission on scales of 10s-1000s au. Our results represent a homogeneous characterisation of the dust and ionised gas properties in Ophiuchus and present a potential solution to the long-standing 'missing disk mass' problem. However, our understanding is still limited by resolution and sensitivity at frequencies <40 GHz. Future facilities like the SKA and ngVLA are needed to provide the necessary capabilities to fully spatially resolve this emission (<0.18") even in one of the closest star-forming regions.

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arXiv2026

ALMA observations of Magnetic Fields in the Massive Star-forming Region IRAS 18360-0537

Assessing the significance of magnetic fields in high-mass star formation remains one of the most challenging topics in astrophysics. In this study, we present full polarization observations obtained from the Atacama Large Millimeter/Submillimeter Array (ALMA) of the high-mass star-forming region IRAS18360-0537. The polarized dust emission at 1.3 mm reveals a clear hourglass-shaped morphology of the magnetic field. Interestingly, the magnetic field orientation is nearly perpendicular to both the outflow and core rotation axes, while it aligns with the elongation of the core. This orientation poses challenges for interpretation, particularly in light of the strong magnetic field strength estimated using the Davis-Chandrasekhar-Fermi method. Several scenarios provide insights into the underlying reasons for this magnetic field morphology. A clear velocity gradient seen in high-density tracing of molecular spectral lines indicates that the core is fast-rotating. The curved outskirts of the magnetic fields coincide with the outflow cavity, suggesting a possible influence from the outflow. The accretion flows along the core's elongation are also notable. Our study shows that the morphology of the magnetic field is probably highly influenced by the gas bulk motions.

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arXiv2026

Substructures in Planet-Forming Disks with the SKAO

Disks of gas and dust orbiting young stars are the arenas and material reservoirs for planet formation. Over the past decade, multiwavelength observations, from infrared to radio, have resolved the spatial distribution of hundreds of protoplanetary disks in nearby star-forming regions, revealing a diverse zoo of substructures. These substructures are morphological features such as rings, gaps, spirals, vortices, asymmetries, warps, or clumps that trace variations in density, temperature, or composition relative to an otherwise smooth distribution of gas and dust. Many unknowns persist as to the origin of these substructures, their role in planet assembly, and their true properties. SKA-Mid Band 5b continuum observations, offering angular resolutions of $\sim 0.05''$ ($\sim 0.15''$) with AA4 (AA*) at $12.5$ GHz / $2.4$ cm, will enable new progress at this frontier. In this chapter, we outline the open questions in the field of disk substructure that SKA-Mid is uniquely poised to address, with a lens on dust thermal emission.

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arXiv2026

Probing Anomalous Microwave Emission with the Square Kilometre Array

Anomalous microwave emission (AME) represents an excess of radiation in the 10-60 GHz range, distinct from synchrotron, free-free, or thermal dust emission. Although most commonly attributed to electric dipole radiation from rapidly rotating small dust grains (spinning dust), alternative mechanisms such as magnetic dipole emission (MDE) remain plausible. The detection of AME across diverse environments, from diffuse interstellar clouds to protoplanetary disks and external galaxies, suggests that multiple physical processes or carriers may contribute to its origin. Understanding AME is essential for both Galactic astrophysics and cosmology, as it constitutes a significant foreground for cosmic microwave background (CMB) studies, potentially biasing measurements. This chapter reviews current theoretical frameworks and observational evidence for AME, highlighting the key outstanding questions concerning its emission mechanisms, carriers, and polarization properties. We discuss how the Square Kilometre Array Observatory (SKAO), through its unprecedented sensitivity, angular resolution, and frequency coverage, will transform AME studies. SKA observations will enable detailed mapping of AME morphology, precise characterisation of its spectral energy distribution, and the identification of its carriers in Galactic and extragalactic environments. By combining SKA-mid data with higher-frequency observations from ALMA and other facilities such as SPHEREx, it will be possible to disentangle competing models and exploit AME as a diagnostic probe of interstellar grain physics and the small-scale structure of the interstellar medium.

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arXiv2026

Magnetic Fields in Massive Star-forming Regions (MagMaR). VII. On the dynamical importance of B-fields in massive protocluster W33 A

Magnetic fields (B-fields) are likely important in massive protocluster formation, but their role remains poorly constrained. We present 1.2 mm ALMA full-polarization observations of W33 A, a massive star-forming region at 2.4 kpc, with an angular resolution of 0.3 arcsec (730 au). The region is resolved into 20 dense cores and 9 filaments. The plane-of-sky B-field, inferred from linearly polarized dust emission, shows diverse structures: two nearly perpendicular large-scale components oriented northwest-southeast (NW-SE) and northeast-southwest (NE-SW), and two localized features toward the millimeter peaks MM1 and MM2. The NW-SE component could be shaped by a molecular outflow. The NE-SW component is coherent along the main filaments F1, F-Main, and Tail, all of which show trans-Alfvenic turbulence. In F-Main, the line mass exceeds the turbulent critical value, implying that magnetic support is required to prevent radial collapse and suppress fragmentation. In F1 and Tail, turbulence alone can support the gas against gravity, although B-fields may provide additional support. Toward MM1, the B-field follows a spiral-like infalling streamer traced by CH3CN. The trans-Alfvenic state of the accreting gas suggests efficient magnetic damping of turbulence and a magnetically regulated, laminar accretion flow feeding the core. Toward MM2, the B-field shows an hourglass morphology fitted by parabolic curves. Two independent methods give a consistent field strength of about 8.1(1.9) mG, and virial analysis indicates that the B-field is dynamically important in delaying collapse of MM2. Within a single protocluster, B-fields can stabilize filaments, regulate accretion, and delay core collapse, highlighting their diverse dynamic role in high-mass star formation.

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