Maria Teresa Beltrán

We present results from Karl G. Jansky Very Large Array radio-continuum observations of 12 intermediate-mass (IM) protostars, as part of the SOFIA Massive Star Formation Survey. Using these observations, we studied their morphology, multiplicity, and radio spectral energy distributions (SEDs). Across our target regions, we resolve multiple compact sources and report eight new detections, four of which are entirely new and four that have counterparts at other wavelengths, but are detected here for the first time at radio frequencies. Based on radio morphologies and spectral indices, we assess the nature of the detected sources, highlighting seven that display jetlike structures and spectral indices consistent with ionized jets. Combining our results with the SOMA Radio I and II results, we expand the overall sample to 29 protostars, covering a bolometric luminosity range from L _bol ∼ 10 ² to 10 ⁶ L _⊙ . These sources help define a potential evolutionary sequence in the radio versus bolometric luminosity diagram. IM protostars have radio luminosities that are lower than expected from a simple power-law extrapolation from low-mass protostars. However, this result is consistent with theoretical expectations from protostellar evolution models, which show low levels of photoionization and reduced shock ionization emission due to expanded stellar radii during this phase. Overall our expanded SOMA Radio sample provides new constraints on theoretical models of massive protostellar evolution, especially the connection to ionized gas structures.

Context . Accretion streamers connected to protostellar disks and/or envelopes are thought to transport material across several thousand of au. Whether the motions of the gas comprising these streamers are dominated by gravity, large scale external turbulence or the action of magnetic fields is still under scrutiny. Aims . The aim of this work is to understand the role of the magnetic fields in the star-formation processes, in particular the role that magnetic forces have in potentially leading flows of gas and accretion onto the envelopes and disks orbiting protostars. Methods . First, we try to identify large-scale accretion streamers toward the high-mass Young Stellar Object GGD 27–MM1 and fit their trajectories using the so-called Mendoza model, a modification of the classical model of pure gravitational infalling motion of fluid particles in a potential well. Second, we estimate the strength of the magnetic field associated with the streamers. Then, we determine whether the streamers are dominated by magnetic or centrifugal forces. Results . Inspecting the Atacama Large Millimeter/submillimeter Array (ALMA) H ₂ CO cube we were able to identify four accretion streamers spreading up to ∼7000 au and fit their trajectories in the position-position-velocity space. The polarized continuum emission reveals a good alignment of the magnetic field and the trajectory of the streamers. Using the Davis-Chandrasekhar-Fermi (DCF) method, we derive estimates for the magnetic field strength, find that the streamers are sub-Alfvénic, and discuss (after estimating energy terms for turbulence, ordered motions, magnetic forces, and gravity) a possible qualitative scenario in which, the gravitational well of the GGD 27–MM1 protostar dominates streamer gas motions over turbulence and magnetic forces at distances of ∼3000 au.

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.

Context . Although there has been significant progress, the physical properties and potential fragmentation of accretion disks around high-mass protostars remain poorly constrained. Aims . We characterize at high angular resolution one of the most nearby (~700 pc) high-mass accretion disk candidates, CepA HW2. Methods . Using the new long-baseline array configuration (~1700 m) of the Northern Extended Millimeter Array (NOEMA), we study CepA HW2 with a resolution of ≤0.2″ or ≤100 au at 1.3 mm in dust continuum and spectral line emission. Results . The millimeter continuum emission resolves the central disk candidate into several substructures. Conducting a Toomre Q stability analysis based on CH ₃ CN and continuum data, and a comparison to 3D radiation hydrodynamic simulations shows that the data are consistent with an almost edge-on disk whereby the observed substructures may represent fragments within the disk. The CO and SiO spectral line data confirm a second bipolar outflow (in addition to the well-known jet) emanating from the central peak position. This indicates that this central peak should host at least a binary if not even a higher-order multiple system. The usually assumed dense gas tracer CH ₃ CN also shows contributions from the outflows, which complicates further kinematic analysis of the disk. Conclusions . The high-resolution outflow-disk data of CepA reveal a multiply fragmented disk that drives several outflows. These observations reinforce the picture of high-mass star formation in which multiplicity and fragmentation can happen on the smallest spatial scales related to the inner accretion disks.

Context . High-mass star-forming regions are rich in complex organic molecules (COMs), which are carbon-bearing species with at least six atoms. Their formation pathways remain debated. The ALMA evolutionary study of high-mass protocluster formation in the GALaxy (ALMAGAL) survey provides a unique opportunity to probe this chemical complexity in a large statistical significant sample of high-mass star-forming regions. Aims . We present a detailed molecular line analysis of one of the most chemically rich cores in the ALMAGAL sample, the high-mass core 9 in the AG318.9477−00.1960 clump (AG318−c9), located at a heliocentric distance of ∼10.4 kpc. This source was selected because it combines an exceptionally high line density with a relatively simple kinematic structure, making it an optimal template for chemical analysis in the survey. We further assessed whether the emission of selected COMs, that is, ethylene glycol ((CH ₂ OH) ₂ ; EG), glycolaldehyde (CH ₂ (OH)CHO; GA), and methyl formate (CH ₃ OCHO; MF), can be used to trace the innermost regions of hot molecular cores (HMCs). Methods . We analysed ALMA Band 6 observations (∼217–221 GHz). Spectral line identification and local thermodynamic equilibrium modelling were performed using the software called MAdrid Data CUBe Analysis (MADCUBA). We derived the physical parameters, including the column density ( N ), excitation temperature ( T _ex ), velocity, line width, and molecular abundances relative to H ₂ , for all detected species. The chemical inventory of AG318−c9 was compared with that of the HMC G31.41 + 0.31 (G31). In addition, we performed a pixel-by-pixel analysis of EG, GA, and MF to generate spatially resolved N and T _ex maps and corresponding radial profiles. Results . We report the detection of 65 molecular species, including 31 main species and 34 isotopologues and vibrationally excited species. Of these, 44 are O-bearing species, 28 are N-bearing, 8 are S-bearing, and 2 are Si-bearing. While AG318−c9 exhibits lower abundances than G31 overall, it shows detections of species that have not yet been reported in G31, such as ethyl formate (C ₂ H ₅ OCHO). Moreover, 12 species depart from the general trend, displaying relative overabundances in AG318−c9. The comparison also reveals a chemical differentiation between O- and N- bearing COMs, with O-bearing species systematically more abundant in G31. Regarding EG, GA, and MF, the latter is the most abundant ( X ∼ 3 × 10 ⁻⁸ ), followed by EG ( X ∼ 7 × 10 ⁻⁹ ) and GA ( X ∼ 2 × 10 ⁻⁹ ). The N and T _ex maps suggest that MF is the most spatially extended species, whereas EG and GA are more compact and confined to the innermost hot region. Conclusions . AG318−c9 reveals a rich chemical inventory characteristic of an HMC. The chemical comparison with G31 suggests that AG318−c9 is a less evolved hot core dominated by the recent sublimation of ice mantles, in contrast to the higher abundances observed in the possible more evolved G31. MF emerges as an excellent tracer of the gas temperature in HMCs owing to its wide spatial extent and wide dynamic range of the excitation temperature. In contrast, EG and GA are more compact and preferentially trace the innermost high-density regions of the core, suggesting a high sublimation temperature threshold and supporting a shared grain-surface formation pathway. While EG and MF seem to be partly limited by sensitivity, GA reflects an intrinsically central distribution.

Magnetohydrodynamic (MHD) disk winds (DWs) can be responsible for removing angular momentum from the accretion disks of protostars, for driving mass accretion and disk evolution and dispersal, and, ultimately, for setting the conditions for planet formation. We want to investigate two massive young stellar objects (YSOs), and where evidence for MHD DWs has been previously obtained at scales of 10--100 au through measurements of the 22 GHz water maser velocity distribution within the Protostellar Outflows at the EarliesT Stages (POETS) survey. The different mass, 5.6±2 and ≈20 of the two YSOs allows us to investigate the dependence of MHD DWs on the YSO environment, too. We employed IRAM Northern Extended Millimeter Array and archival Atacama Large Millimeter Array observations of and respectively, to study the gas kinematics and physical conditions of the corresponding protostellar winds on scales of 100--1000 au using the same molecular tracers. In the emissions of several molecules, particularly SO, SO_2, CH_3CN, and CH_3OH, are distributed along the axis of the previously identified radio jet, and present a local standard of rest (LSR) velocity ( gradient transversal to the jet axis. Position-velocity (PV) plots of the SO lines show patterns consistent with Keplerian rotation. The SO_2 emission comes from high-velocity gas flowing close to the jet axis, while CH_3CN and CH_3OH present a larger radial extension than the S-bearing species. In the same molecules are instead distributed along the (sky-projected) major axis of the rotating disk reported previously, and their gradients consistently trace the disk rotation. The corresponding PV plots present Keplerian profiles. SO is the only molecular species whose emission extends well outside the disk. Our analysis shows that, in both YSOs, the spatial and velocity distributions of SO are consistent with a rotating wind magneto-centrifugally launched from the YSO disk. The comparison with models of molecule formation and excitation in shocks indicates that the different radial extension of the molecular species observed in the protostellar wind of as well as the lack of molecules, except SO, in the wind, can be well explained in terms of a radially extended MHD DW, rather than a compact X-wind. This study provides compelling evidence that the SO and SO_2 emissions can be used to trace MHD DWs in luminous YSOs at scales of 100--1000 au, and confirms the results derived with water masers at scales of 10--100 au.

Context . Several theoretical and observational studies have shown that new waves of triggered star formation can be induced by the feedback from newly formed massive protostars, due to the expansion of H II regions. Aims . We used the millimeter dust continuum data of the ALMAGAL survey and the Anderson et al. (2014) catalog of H II regions to search for signatures of possible triggered star formation at its onset, and selected one ALMAGAL source for ALMA follow-up observations. Methods . For this study we selected the source AG286.0716–1.8229, in which six cores were detected at a resolution of ~7600 au, but only two at a higher resolution. The four cores not detected at higher resolution are prestellar core candidates. We used archival data from the SARAO Meerkat Galactic Plane Survey and Rapid Askap Continuum Survey to confirm whether a H II region is present in the field. We observed the source with ALMA in Band 4, covering the emission of DCO ⁺ (2–1), N ₂ D ⁺ (2–1), DCN (2–1), and CH ₃ CCH (9–8), to infer from the chemical composition and temperature estimates whether these cores are in an early phase of the star-formation process, which allows us to classify them as prestellar cores. The new Band 4 continuum image revealed additional three cores outside of the ALMAGAL field of view (FoV), making a total of nine cores in the region, eight of which are located along an arch that has a radius of ~0.75 pc. We also used the continuum and molecular emission to estimate the mass of these cores, to determine whether they are gravitationally bound or transient objects. Results . We have derived a spectral index between −0.14 and −0.4, in the frequency range of 0.8–1.6 GHz for the candidateH II region, which is consistent with optically thin free-free emission. The H II region spatially coincides (as projected on the plane of the sky) with the position of one of the cores, which in the new ALMA Band 4 observations does not have a compact morphology. The N ₂ D ⁺ and DCO ⁺ emission peaks at the position of three out of four prestellar core candidates, and the overall emission in both the line and the continuum, which extends outside of the FoV of the ALMAGAL observations, reveals a clear arched shape centered on the H II region. We were able to estimate the gas temperature of only the most evolved core, using the CH ₃ CCH emission. The resulting value of 39 ± 5 K is also an upper limit for the other cores. Using plausible temperature ranges for each core, based on the information from chemical tracers and the dust continuum, we derived mass ranges for the cores (~2–16 M _⊙ ) as well as ranges for the virial parameter (~0.3–5). All the cores along the arch have virial parameters consistent with bound objects, with only one exception. Conclusions . Comparing the typical separation and mass of the cores with those expected in the case of the collect and collapse scenario and with the thermal Jean length and mass, the best agreement is found with the characteristic scales in the case of triggered star formation. The same methodology can be applied to further ALMAGAL sources to identify optimal targets to study a larger sample of prestellar cores in an environment affected by the presence of a H II region.

Context . High-mass stars and star clusters form from the fragmentation of massive dense clumps driven by gravity, turbulence, and magnetic fields. The extent to which each of these agents impacts the fragmentation depending on the clump mass, density, and evolutionary stage is still largely unknown. Aims . The ALMA evolutionary study of high-mass protocluster formation in the GALaxy (ALMAGAL) project, with ∼1000 clumps observed at ∼1000 au resolution, allows a statistically significant characterization of the fragmentation process over a large range of clump physical parameters and evolutionary stages. Our goal is to characterize where and how the dense cores revealed by ALMA are distributed in massive potentially cluster-forming clumps to trace how fragmentation is initially set and how it proceeds before gas dispersal due to stellar feedback. Methods . We characterized the spatial distribution of dense cores in the 514 ALMAGAL clumps that host at least four cores, using a set of quantitative descriptors that we evaluated against the clump bolometric luminosity-to-mass ratio, which we adopted as an indicator of the evolution of the system. We measured the separations between cores with the minimum spanning tree (MST) method, which we compared with the predictions of gravitational fragmentation from Jeans theory. We investigated whether cores have specific arrangements using the Q parameter or variations due to their masses with the mass segregation ratio, Λ _MSR . Results . ALMAGAL cores are distributed throughout the entire area of the clump, usually arranged in elliptical groups with an axis ratio e ∼2.2, although high values with e ≥ 5 are also observed. We found a single characteristic core separation per clump in ∼76% of cases, suggesting that multiple fragmentation lengths may be frequently present. Typical core separations are compatible with the clump-averaged thermal Jeans length, λ _J ^th . However, we found an additional population of cores, typical of low-fragmented and young clumps, which are on average more widely separated with l ≈ 3 × λ _J ^th . By stacking the distributions of the core separations in clumps of similar evolutionary stage, we also found that the separation decreases on average from l ∼22 000 au in younger systems to l ∼7000 au in more evolved ones. The ALMAGAL cores are typically distributed in fractal-type subclusters, while centrally concentrated patterns appear only at later stages, but we do not observe a progressive transition between these configurations with evolution. Finally, we also found 110 ALMAGAL systems with a signature of mass segregation, with an occurrence that increases with evolution.