Pamela D. Klaassen

Molecular winds may play a key role in governing angular momentum transport and accretion during the early evolution of protostars. We present the morphology and kinematic properties of the H ₂ emission in five young, envelope-dominated protostars across a broad bolometric luminosity range, from 0.2 to 10 ⁴ L _⊙ , observed with the NIRSpec/integral field unit and MIRI/Medium Resolution Spectrograph on board JWST as part of the Investigating Protostellar Accretion (IPA) program. A rich set of pure rotational lines of H ₂ , up to v = 0–0 S (18), and a few rovibrational lines are detected in the winds, revealing bipolar structures. The H ₂ lines show a stratified/onion-like structure morphologically and kinematically, where the lines with higher E _u / k show a higher degree of collimation and higher velocities. Additionally, the wind velocity scales with the L _bol of the host protostellar system. In four out of five protostars, H ₂ emission fills the outflow cavity without showing pronounced limb brightening. We also report a tentative detection of H ₂ wind rotation in IRAS 16253, which suggests a launch radius of ∼4 au and a magnetic lever arm parameter of ∼5–10. Taken together, these properties of the H ₂ winds can be explained by the magnetohydrodynamic disk wind models. We detect a collimated, high-velocity H ₂ jet toward HOPS 370, which is more evolved than the extremely young source HH 211 but is accreting at a high accretion rate. This suggests that the presence of collimated molecular jets in protostars is more closely connected to accretion rate than system age.

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. The northwest photodissociation region (PDR) of the NGC 7023 reflection nebula has been observed with JWST spectroscopy, revealing the carbonaceous emission bands at a high level of detail. Compared to other PDRs (Horsehead and Orion Bar) the softer radiation field driving NGC 7023 results in an extended atomic hydrogen region and more pronounced spatial variations in the band profiles. Its weaker thermal dust continuum makes NGC 7023 an ideal target for studying the 16–18 µm emission and its relation to the main emission bands at 3.3, 3.4, 5.2, 5.7, 6.2, 7.7, 8.6, 11.3, and 12.7 µm. Aims. We performed a spatially resolved study to reveal which emission bands originate from the same or cospatial populations of small carbonaceous emitters. Methods. We applied a spectral decomposition with PAHFIT to around 500 extracted spectra and produced maps of the individual subcomponents of the carbonaceous emission bands. The spatial resolution of around 0.7 mpc effectively resolved the dissociation front. Results. Nearly all feature maps peak at the dissociation front (DF1), while the emission in the atomic PDR region (ATM) varies strongly between the bands and their subcomponents. We organized the spatial distributions into three categories based on the intensity ratio in ATM relative to DF1. Most bands are of type I (low ATM/DF1; 3.3, 3.4, 5.2, 5.7, 11.3 µm) or II (medium ATM/DF1; 16.2, 7.7, 8.6, 12.7, 16.4 µm), while only few are of type III (high ATM/DF1; 11.0, 17.4 µm). The decompositions and maps of the 5.7, 7.7, 11.3, and 12.7 µm bands reveal that their bluer subcomponents are of type III, while their redder subcomponents are of type I or II. The 17.4 µm band correlates strongly with these blue subcomponents and the 8.6 and 11.0 µm features, which trace charged carriers. Conclusions. The wide range of 17.4 and 16.4 µm spatial distributions indicate at least two different populations contributing to the 16–18 µm range. The strongly differing spatial distribution types of carbonaceous band subcomponents reveal a connection between the 11.0 and 17.4 µm bands and the spectral profiles of the 5.7, 7.7, 11.3, and 12.7 µm bands. The maps indicate that these profiles will continue evolving as the central cavity is approached. Since C ₆₀ emission was previously detected in the cavity, we speculate that the population of emission carriers could be in an intermediate photochemical evolution stage of fullerene formation.

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. The formation and destruction of molecules in the interstellar medium involve a complex interplay between gas phase reactions, as well as processes on grain surfaces and within icy mantles. In recent decades, the gas phase composition of the cold material toward star-forming regions could be well characterized using (sub)millimeter facilities. Prior to the launch of the James Webb Space Telescope (JWST), ice species other than the main constituents (i.e., H ₂ O, CO, CO ₂ , NH ₃ , CH ₄ , and CH ₃ OH) were challenging to detect due to insufficient sensitivity as well as angular and/or spectral resolution. Aims. We aim to determine molecular ice and gas phase column densities toward the young and embedded high-mass hot core IRAS 18089-1732 within a region of 5000 au. Methods. We used spectroscopic data from 5 to 28 μm obtained with JWST to derive the ice column densities of H ₂ O, SO ₂ , OCN ⁻ , CH ₄ , HCOO ⁻ , HCOOH, CH ₃ CHO, CH ₃ COOH, C ₂ H ₅ OH, CH ₃ OCH ₃ , and CH ₃ COCH ₃ . We inferred the gas phase column densities for a total of 38 molecules, including O-, N-, S-, and Si-bearing species, as well as less abundant isotopologs, from sensitive molecular line observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) at 3 mm wavelengths. Results. We find comparable abundances (relative to C ₂ H ₅ OH or CH ₃ OH) in both phases for C ₂ H ₅ OH, CH ₃ OH, and CH ₃ OCH ₃ . The abundances of SO ₂ and CH ₃ COCH ₃ are higher in the gas phase, suggesting additional gas phase formation routes. The abundance of CH ₃ CHO is one order of magnitude higher in the ices compared to the gas phase. The ice abundances (relative to H ₂ O ice) toward the IRAS 18089 hot core are similar to previously studied Galactic low- and high-mass protostars. There are hints of a decreasing abundance with galactocentric distance for OCN ⁻ , CH ₃ OH, and CH ₃ CHO ices. Conclusions. It is evident that not all species show comparable abundances in the ice and gas phases. However, we do find similar trends when species show elevated ice or gas phase abundances in the high-mass hot core IRAS 18089, compared to low-mass hot cores. To better understand the reaction pathways of molecular species, statistical surveys analyzing both the ice and gas phase chemical composition of high- and low-mass protostars at different Galactocentric radii are essential.

Context. While many aspects of high-mass star formation have been investigated, the accretion onto the central protostars is one of the most fundamental but less explored physical properties. The James Webb Space Telescope (JWST), through its Mid InfraRed Instrument (MIRI), offers a unique opportunity to explore tracers of accretion at less-extincted wavelengths (5–27 μm) than those studied so far, where it delivers unparalleled sensitivity and spectral resolution. Aims. We probed the capability of MIRI in its MRS/IFU mode to detect and resolve atomic Hydrogen (H I ) emission lines in such embedded objects to subsequently estimate accretion luminosities ( L _acc ) and accretion rates ( Ṁ _acc ) for the first time in a sample of (six) high-mass, star forming regions at different evolutionary stages. Methods. We used the dereddened H I line luminosities as tracers of accretion by applying line-to-accretion-luminosity relations ( L _acc -calibrations) from the literature. As such L _acc -calibrations were originally established for low-mass Class II objects, we assessed their applicability to our sample prior to estimating accretion rates. Extinction was derived from the silicate absorption feature at 9.7 μm. Results. The infrared continuum reveals, at much higher spatial resolution than before, the location of new infrared sources (protostars), towards which we detected a handful of H I lines. While a few lines are secure detections, many are tentative. The most commonly detected line is Humphreys α at 12.37 μm, followed by Humphreys β and Pfund α . Assuming that their line fluxes are dominated by accretion, we find that two of the three existing L _acc -calibrations predict excessively high accretion luminosities that largely exceed their bolometric luminosities ( L _bol ), and that the third L _acc -calibration still overpredicts accretion luminosities for some sources. Considering the given uncertainties, estimated accretion rates are only tentative. Conclusions. This work demonstrates the great potential of JWST/MIRI to probe H I line emission that originated in the innermost regions of high-mass protostellar systems, setting the ground floor for further investigations into accretion in these objects. While this project had the ambitious goal of robustly quantifying accretion rates, we shed light on what outstanding methodological challenges remain; the most critical being the development of new L _acc - calibrations for intermediate- to high-mass protostars.

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.