Yuxin Lin

Context. The ∼0.1 pc hot molecular core (HMC) in the massive molecular clump G31.41+0.31 (G31) is one of the clearest examples of an hourglass-shaped magnetic field (B field) in a high-mass star-forming region. However, the B field in the ∼0.1–0.4 pc parent clump remains relatively unexplored at high angular resolutions. Aims. We aim to investigate the multi-scale evolution of the B field in G31, including its morphology, strength, and dynamical importance in G31. Methods. We performed the ∼2″ (∼0.04 pc) angular-resolution JVLA Q-band (∼7 mm) dust polarization observations toward G31, which represents one of the earliest dust polarization observations on high-mass star-forming regions at this wavelength. We jointly analyzed the Q-band observation with the previous higher-resolution ALMA 1.3 mm dust polarization observations. A simple radiative transfer model was used to determine the polarization mechanism observed. We used 3D full polarization radiative transfer modeling and synthetic observations to constrain the B-field morphology threading the G31 clump and core. Angular dispersion analysis was used to estimate average B-field strengths. The energetics was then estimated from the clump to the core. Results. The JVLA observations resolve linearly polarized intensity with rather uniform polarization position angles in the inner ∼0.4 pc region, which indicates a relatively strong and uniform B field on ≲0.4 pc scales. We find that our 7 mm observations and the previous ALMA observations can be coherently explained with a multi-scale B-field configuration: a large-scale uniform field encompassing a central hourglass shape. The average B-field strength is estimated to be ∼8–11 mG. We estimated that from ∼0.4 pc to ∼0.04 pc scales, the magnetic critical parameter, λ, increases from 1.3 to 2.3, and the Alfvén Mach number, M _A , increases from 0.4 to 1.5. This likely indicates a transition from a trans-critical, sub-Alfvénic regime at the clump scale to a supercritical, super-Alfvénic regime at the core scale. Conclusions. A concordant explanation for these results is that the initially uniform B field is dragged by the rapid self-gravitational collapse around the HMC. The gravitational contraction and/or the (proto)stellar feedback may enhance turbulence around the HMC.

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 _vir ). Using a James Clerk Maxwell Telescope SCUBA2 850 μ m 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 _vir , indicating that they are predominantly gravitationally unbound at the ∼86 pc resolution of our observations. While no statistically significant global correlation is found between SFE and α _vir for the full cloud sample, the upper quantiles of the SFE distribution show progressively stronger negative trends with increasing α _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 _vir CO-bright clouds in the observed sample. The substantial scatter in the SFE- α _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 _vir and instantaneous SFE difficult to recover for individual GMCs.

Context . Studying the chemical composition of the warm gas surrounding embedded solar-type protostars is one of the areas for which the Atacama Large Millimeter/submillimeter Array (ALMA) is particularly well suited. Recently, the ALMA Large Program Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) carried out an observing campaign of a sample of 11 protostellar regions to investigate the chemical impact of their environments and evolutionary stages. Aims . The aim of this paper is to provide the observational and procedural information necessary for the community to understand the analysis presented in forthcoming scientific papers by the COMPASS collaboration, and to enable archival research using the data products provided by our team and the ALMA Science Archive. Methods . This paper describes the technical setup of the observations, and it outlines the data-processing pipeline and primary data products from this initiative. The Common Astronomy Software Applications (CASA) was used for initial calibration following the standard ALMA Pipeline, and then IMAGER was used for self-calibration and imaging. We describe post-processing done with Python to achieve favorable continuum subtraction, correct for the primary beam response, and extract spectra. Results . We discuss our strategy for mitigating data challenges, including those related to data volume and continuum subtraction for spectral line analysis. The incorporation of IMAGER in our workflow was advantageous in terms of the computing efficiency which allowed us to benchmark several imaging parameters and techniques; we also demonstrate that the imaging outcomes using IMAGER or CASA are scientifically comparable. Numerous data products are generated for the program, including image cubes for the 36 spectral windows targeting each source, extracted spectra, and continuum images.

Context . Methanol is a complex organic molecule detected in both ice and gas toward star-forming regions. Due to its high abundance, its rarer isotopologues, including the deuterated ones, are also commonly detected. Measurements of deuteration can provide key constraints on the formation and evolution of molecules during the formation of stars and planets. It is not clear how the methanol deuteration varies between star-forming regions. Thanks to several recent spectroscopic studies, it is now possible to precisely derive the column densities of five deuterated isotopologues of methanol. Aims . Our aim is to determine the column density and deuterium fractionation of methanol in the low-mass protostar BHR71-IRS1. Methods . We analyzed data from a large spectral survey of BHR71-IRS1 carried out as part of the ALMA Large Program Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS). We used the CASSIS software to identify the lines of the methanol isotopologues and constrain their column densities under the assumption of local thermodynamic equilibrium. Results . We detected CH ₃ OH, ¹³ CH ₃ OH, CH ₃ ¹⁸ OH, CH ₃ OD, CH ₂ DOH, CHD ₂ OH, and CD ₃ OH at the continuum peak position. In addition, CH ₃ ¹⁷ OH is tentatively detected, while CD ₃ OD is not detected, although a few faint lines (≲3 σ ) could be present toward a position redshifted from the continuum peak. The column densities of the main isotopologue obtained from ¹³ CH ₃ OH and CH ₃ ¹⁸ OH are consistent, assuming nominal ¹² C/ ¹³ C and ¹⁶ O/ ¹⁸ O ratios of 68 and 557, respectively. The CH ₂ DOH/CH ₃ OD column density ratio is equal to 7 ± 2. The statistically corrected D/H ratio is higher for CH ₂ DOH (1.9 ± 0.6%) than for CH ₃ OD (0.8 ± 0.2%). The level of deuteration after statistical correction increases with the number of D atoms in the methyl group, reaching 23 ± 5% for CD ₃ OH/CH ₃ OH. Conclusions . These trends are similar to other low-mass protostars such as IRAS 16293–2422 and HOPS 373SW, but seem to differ from the eruptive young star V883-Ori. Similar studies with comparable datasets will be carried out for the other COMPASS sources to determine if factors such as environmental conditions and evolutionary states impact the deuteration of methanol.

Context . It remains a fundamental research question in astrochemistry to characterize the inventory of complex organic molecules formed during the early stages of star formation, which may affect the eventual chemical composition of protoplanetary disks and potentially planets. So far, only studies of individual sources or selected samples of molecular species have been conducted and the relative importance of environmental and evolutionary effects on the chemical composition remains unclear. Aims . The Atacama Large Millimeter/submillimeter Array (ALMA) provides the angular resolution and sensitivity to zoom in on the hot ( T > 100 K) gas surrounding embedded solar-type protostars and chart their molecular inventories with high accuracy. The ALMA Large Program Complex Organic Molecules in Protostars with ALMA Spectral Surveys (COMPASS) aims to provide comprehensive inventories of the molecular content of a sample of protostellar sources to understand the chemical impact of their environments and evolutionary stages. Methods . COMPASS is an unbiased spectral survey of 11 line-rich Class 0 and I protostellar sources in the spectral range from 279.0 to 311.7 GHz at 0.15–0.5″ angular resolution with ALMA, corresponding to the inner ∼100 au (radius) around the targeted sources. Through this survey, unique chemical fingerprints of each source can be established. Results . This paper provides an overview of the COMPASS program and the adopted strategy in terms of observational setups and targeted sources. We also present a qualitative comparison of the spatial distributions of selected molecules and the relative strengths of the line fluxes of selected complex organics. Conclusions . The qualitative comparisons suggest that chemical differences between sources may be present, for example, between the abundances of groups of oxygen- and nitrogen-bearing species, but also that such variations occur at levels smaller than an order of magnitude. Quantitative comparisons of abundances at these levels require the large bandwidth of the survey, as well as a careful analysis of the excitation and strengths of the several thousands of lines detected toward each source in the survey, as will be explored in forthcoming papers.

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 4 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 multiline 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.

Magnetic fields play a crucial yet complex role in star formation, while their connection between large-scale filamentary clouds and small-scale young stellar objects remains poorly understood. We present new continuum polarization observations from the JCMT, ACA, and ALMA that provide continuous magnetic field measurements from ∼5 pc down to ∼4000 au, tracing for the first time the evolution of field morphology seamlessly across all key scales within a massive star-forming system. Our polarization maps reveal multiple U-shaped magnetic field structures pointing toward the central protocluster, aligned with accreting filaments from parsec- to subparsec-scales and converging at the compact center. This morphology suggests an environment of colliding flows that drag magnetic fields and trigger massive protocluster formation. On ∼4000 au scales, we identify compact U-shaped fields likely guiding the kinematics of streamers accreting onto dense cores. The increasing curvature of these U-shaped patterns is a direct measure of a growing magnetic field tension force, implying a magnetic field strength scaling index of 0.50 ± 0.10. These results indicate that the field, possibly enhanced by large-scale flow collisions, becomes strong enough to regulate star formation, linking parsec-scale colliding flows, a subparsec hub–filament system, and the triggering of massive star formation.

Context . Shock chemistry is an excellent tool for shedding light on the formation and destruction mechanisms of complex organic molecules (COMs). The L1157-mm outflow is the only low-mass protostellar outflow that has extensively been studied in this regard. Aims . We mapped COM emission and derived the molecular composition of the protostellar outflow driven by the Class 0 protostar NGC 1333 IRAS 4B1 to introduce it as a new laboratory for studying the effect of shocks on COM chemistry. Methods . We used the data taken as part of the PROtostars & DIsks: Global Evolution (PRODIGE) large program to compute integrated-intensity maps of outflow emission to identify spatial differences between species. The emission spectra were then analysed towards two positions, one in each outflow lobe, by deriving synthetic spectra and population diagrams assuming conditions of local thermodynamic equilibrium. Results . In addition to typical outflow tracers such as SiO and CO, outflow emission is seen from H ₂ CO, HNCO, and HC ₃ N, as well as from the COMs CH ₃ OH, CH ₃ CN, and CH ₃ CHO, and even from deuterated species such as DCN, D ₂ CO, and CH ₂ DOH. The maps of integrated-intensity ratios between CH ₃ OH and DCN, D ₂ CO, and CH ₃ CHO reveal gradients with distance from the protostar. For DCN and D ₂ CO, this may reflect their pre-stellar abundance profile, provided the outflow is young enough, while an explanation is still required for CH ₃ CHO. Intensity ratio maps of HC ₃ N and CH ₃ CN with respect to CH ₃ OH peak in the southern lobe where the temperatures are highest. This might indicate enhanced HC ₃ N and CH ₃ CN formation at this location, potentially in the warmer gas phase. Rotational temperatures are found in the range ∼50-100K, which is warmer on average than for the L1157-B1 shock spot (≲ 30K). The abundances with respect to CH ₃ OH are higher by factors of a few than for L1157-B1. Conclusions . For the first time, we securely detected the COMs CH ₃ CN, CH ₃ CHO, and CH ₂ DOH in the IRAS 4B1 outflow, serendipitously with a limited sensitivity and bandwidth. Targeted observations will enable the discovery of new COMs and a more detailed analysis of their emission. The morphological differences between the molecules in the IRAS 4B1 outflow lobes and their relative abundances provide first proof that this outflow is a promising new laboratory for shock chemistry, which will offer crucial information on COM formation and destruction as well as on outflow structure and kinematics.

Shock chemistry is an excellent tool to shed light on the formation and destruction mechanisms of complex organic molecules (COMs). The L1157-mm outflow is the only low-mass protostellar outflow that has extensively been studied in this regard. Using the data taken as part of the PRODIGE (PROtostars & DIsks: Global Evolution) large program, we aim to map COM emission and derive the molecular composition of the protostellar outflow driven by the Class 0 protostar NGC1333 IRAS4B1 to introduce it as a new laboratory to study the impact of shocks on COM chemistry. In addition to typical outflow tracers such as SiO and CO, outflow emission is seen from H2CO, HNCO, and HC3N, as well as from the COMs CH3OH, CH3CN, and CH3CHO, and even from deuterated species such as DCN, D2CO, and CH2DOH. Maps of integrated intensity ratios between CH3OH and DCN, D2CO, and CH3CHO reveal gradients with distance from the protostar. Intensity ratio maps of HC3N and CH3CN with respect to CH3OH peak in the southern lobe where temperatures are highest. Rotational temperatures derived towards two positions, one in each lobe, are found in the range ~50-100 K. Abundances with respect to CH3OH are higher by factors of a few than for the L1157-B1. In conclusion, for the first time, we securely detected the COMs CH3CN, CH3CHO, and CH2DOH in the IRAS 4B1 outflow, serendipitously with limited sensitivity and bandwidth. Targeted observations will enable the discovery of new COMs and a more detailed analysis of their emission. Morphological differences between molecules in the IRAS 4B1 outflow lobes and their relative abundances provide first proof that this outflow is a promising new laboratory for shock chemistry, which will offer crucial information on COM formation and destruction as well as outflow structure and kinematics.

Context . Deuterated molecules are a useful diagnostic tool to probe the evolution and the kinematics in the earliest stages of star formation. Due to the low temperatures and high densities in the centre of pre-stellar cores, the deuterium fraction is enhanced by several orders of magnitude with respect to the cosmic D/H abundance ratio. Aims . We study the distribution of the emission and the deuteration of the two carbon chains HC ₃ N and CH ₃ CCH throughout the prototypical pre-stellar core L1544. Methods . We analyse emission maps of CH ₃ CCH, CH ₂ DCCH, CH ₃ CCD, HC ₃ N, HCC ¹³ CN, and DC ₃ N, observed towards L1544 with the IRAM 30 m single-dish radio telescope. We use non-local thermodynamic equilibrium radiative transfer calculations, combined with chemical modelling of the molecular abundances, to constrain physical parameters of the observed species. Following this, we derive the corresponding column density and deuteration maps and analyse the chemical processes influencing the different molecular distributions. Results . We find levels of deuteration of N(DC ₃ N)/N(HC ₃ N) = 0.04-0.07, N(CH ₂ DCCH)/N(CH ₃ CCH) = 0.09-0.15, and N(CH ₃ CCD)/N(CH ₃ CCH) = 0.07-0.09. The deuteration of HC ₃ N appears homogeneous across the core, with widespread D-fraction values above 0.06, tracing intermediate-density gas in the outer layers of the core, at densities less than 10 ⁵ cm ⁻³ . CH ₃ CCD is most efficiently formed in the higher-density regions towards the core centre, while the deuteration fraction of CH ₂ DCCH traces a local density enhancement in the north-east of the core, coinciding with the CH ₃ OH emission peak. Conclusions . The results suggest that gas-phase reactions dominate the formation and deuteration of both HC ₃ N and CH ₃ CCH in L1544, with spatial variations driven by physical structure, density and external radiation. The significantly higher deuteration fraction of CH ₂ DCCH compared to CH ₃ CCD and a tentative gradient with higher values in the north suggest that there are different deuteration mechanisms for the two functional groups, with varying efficiency across the core. Similarities between the CH ₂ DCCH emission and CH ₂ DOH might indicate an additional deuteration pathway of CH ₃ CCH on the surfaces of dust grains, as observed for H ₂ CO.