arXiv subjects

M. T. Valdivia-Mena

Publications and source records attributed to M. T. Valdivia-Mena.

16 recordsLinked to original sources

arXiv2026

PRODIGE - envelope to disk with NOEMA: VII. (Complex) organic molecules in the NGC1333 IRAS4B1 outflow: A new laboratory for shock chemistry

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.

astro-ph.GA↗

arXiv2025

First results from ALPPS: a sub-Alfvénic streamer in SVS13A

We present the first results from the ALMA Perseus Polarization Survey (ALPPS), focusing on the magnetic field in the SVS13A circumbinary disk. The dataset includes full-Stokes dust continuum observations at $\sim0\farcs3$ and 870 $μ$m, as well as molecular line emission from C$^{17}$O$(J=3 \rightarrow 2)$ at $\sim0\farcs3$, C$^{18}$O$(J=2 \rightarrow 1)$ at $\sim0\farcs2$, and DCN$(J=3 \rightarrow 2)$ at $\sim0\farcs1$ angular resolution. Our observations resolve both a previously identified dust spiral and an infalling streamer, capturing their spatial and kinematic structures. The streamer is traced from scales $>300$ au down to the circumbinary disk. Using alignment measure (AM) maps and histograms that compare the orientations of the plane-of-sky magnetic field with local intensity and velocity gradients, we find that the AM distribution peaks at a value of 1. This AM peak strongly suggests alignment between the field and the dust total intensity emission, as well as between the field and the gas velocity, which in turn suggests grain alignment by magnetic fields. From our data, we derive a magnetic field strength, B$_{\mathrm{pos}} \sim 1.1 \pm 0.6$\, mG, and a kinetic to magnetic energy ratio of $0.5 \pm 0.4$, suggesting magnetic dominance. We also produced a map of the Alfvénic Mach number, finding $\mathcal{M}_{\rm A} < 1$ along the streamer, consistent with sub-Alfvénic infalling motions. Therefore, the field is likely facilitating the inflow of material from the envelope onto the disk by constraining movement across the field lines. This represents the first detection of a magnetically sub-Alfvénic infalling streamer in a protostellar system.

astro-ph.GA↗

arXiv2025

Chemical segregation analysed with unsupervised clustering

Molecular emission is a powerful tool for studying the physical and chemical structures of dense cores. The distribution and abundance of different molecules provide information on the chemical composition and physical properties in these cores. We study the chemical segregation of three molecules (c-C$_3$H$_2$, CH$_3$OH, CH$_3$CCH) in the starless cores B68 and L1521E, and the prestellar core L1544. We applied the density-based clustering algorithms DBSCAN and HDBSCAN to identify chemical and physical structures within these cores. To enable cross-core comparisons, the input samples were characterised based on their physical environment, discarding the 2D spatial information. The clustering analysis showed significant chemical differentiation across the cores, successfully reproducing the known molecular segregation of c-C$_3$H$_2$ and CH$_3$OH in all three cores. Furthermore, it identifies a segregation between c-C$_3$H$_2$ and CH$_3$CCH, which is not apparent from the emission maps. Key features driving the clustering are integrated intensity, velocity offset, H$_2$ column density, and H$_2$ column density gradient. Different environmental conditions are reflected in the variations in the feature relevance across the cores. This study shows that density-based clustering provides valuable insights into chemical and physical structures of starless cores. It demonstrates that already small datasets of two or three molecules can yield meaningful results. This new approach revealed similarities in the clustering patterns of CH$_3$OH and CH$_3$CCH relative to c-C$_3$H$_2$, suggesting that c-C$_3$H$_2$ traces regions of lower density than to the other two molecules. This allowed for insight into the CH$_3$CCH peak in L1544, which appears to trace a landing point of chemically fresh gas that is accreted to the core, highlighting the impact of accretion processes on molecular distributions.

astro-ph.GA↗

arXiv2025

ANTIHEROES-PRODIGE: Quantifying the connection from envelope to disk with the IRAM 30m telescope and NOEMA I. Attack of the streamers: L1448N's fight for order in the chaos

Star formation is a hierarchical process ranging from molecular clouds down to individual protostars. In particular how infalling asymmetric structures, called streamers, delivering new material onto protostellar systems, are connected to the surrounding envelope is not understood. We investigate the connection between the cloud material at 10000 au scales down to 300 au scales towards L1448N in the Perseus star-forming region hosting three young Class 0/I protostellar systems. Sensitive molecular line observations taken with the IRAM 30m telescope and NOEMA at 1.4 mm are used to study the kinematic properties in the region traced by the molecular lines. Several infalling streamers are associated with the protostellar systems, some of them traced by C18O and DCN, while one of them is bright in SO and SO2. The kinematic properties of the former streamers are consistent with the velocities observed at large envelope scales of 10000 au, while the latter case show different kinematics. The masses and infall rates of the streamers are 0.01 Msun and 0.01-0.1 Msun and 10^-6 Msun/yr and 5-18x10^-6 Msun/yr for IRS3A and IRS3C, respectively. The envelope mass in the L1448N region is ~16Msun, thus the mass of a single streamer is low compared to the envelope mass (<1%). However, compared to the estimated mass of the protostellar systems a single streamer could deliver up to 1% and 8-17% of mass towards IRS3A (M*~1.2 Msun) and IRS3C (M*~1 Msun), respectively. The rotational signatures of structures in L1448N are all connected - from the large-scale envelope, infalling streamers, down to the rotation of all three disks. Two of the three Class 0/I protostellar systems are still fed by this surrounding material, which can be associated to the remnant envelope. However, we also find a streamer that is bright in SO and SO2 towards IRS3C that could be connected to a nearby sulfur reservoir.

astro-ph.SR↗

arXiv2025

PRODIGE VI -- Envelope to Disk with NOEMA: VI. The Missing Sulfur Problem

Determining the amount of sulfur in volatiles and refractories in the ISM remains one of the main problems in astrochemistry. The detection of H$_2$S ices, which are thought to be one of the main sulfur reservoirs, has not been achieved yet, and the only S-bearing species detected in the ices to date is OCS. PRODIGE large survey observations with NOEMA of several Class 0/I protostars in the Perseus Molecular Cloud provide a perfect opportunity to study the H$_2$S and OCS composition of the ices through the volatiles sublimated in the warm inner core (T$>$100K, n $\sim10^6$cm$^{-3}$) of these protostars. Our aim is to determine the H$_2$S/OCS ratio in the warm inner core of 24 protostars in order to study how it is affected by different factors during its evolution. We used the NOEMA millimeter observations from the PRODIGE program of H$_2$S, H$_2^{33}$S, OCS, OC$^{33}$S and OC$^{34}$S to estimate the H$_2$S and OCS column densities in the warm inner cores. We used SO and SO$_2$ data from the ALMA archive to give a rough estimate of the total sulfur abundance. We explore the chemistry of H$_2$S and OCS in the warm cores using chemical and dynamical simulations of the collapse of a dense core to form a protostar. The estimated H$_2$S/OCS ratio reveals a segregation of the sources into ``OCS-poor'' and ``OCS-rich'' protostars, where the OCS-poor protostars present higher H$_2$S/OCS ratios than the OCS-rich ones. Total sulfur abundance is always dominated by either H$_2$S or OCS, grows with evolution during the Class 0 phase up to $D_S<8$, and decreases again in the Class I. Simulations show that temperature changes in the pre-stellar phase and during the collapse can produce substantial differences in the H$_2$S and OCS abundances and in the H$_2$S/OCS ratio. Our analysis shows that the H$_2$S/OCS ratio is strongly influenced by the environment and the initial conditions of the cloud.

astro-ph.GA↗

arXiv2025

Dense clumps survive in the vicinity of R136 in 30 Doradus

Context: The young massive cluster R136 at the center of 30 Doradus (30 Dor) in the Large Magellanic Cloud (LMC) generates a cavity in the surrounding molecular cloud. However, there is molecular gas between 2 and 10 pc in projection from R136's center. The region, known as the Stapler nebula, hosts the closest known molecular gas clouds to R136. Aims: We investigated the properties of molecular gas in the Stapler nebula to better understand why these clouds survive so close in projection to R136. Methods: We used Atacama Large Millimeter/Sub-millimeter Array 7m observations in Band 7 (345 GHz) of continuum emission, $^{12}$CO and $^{13}$CO, together with dense gas tracers CS, HCO$^+$, and HCN. Our observations resolve the molecular clouds in the nebula into individual, parsec-sized clumps. We determined the physical properties of the clumps using both dust and molecular emission, and compared the emission properties observed close to R136 to other clouds in the LMC. Results: The densest clumps in our sample, where we observe CS, HCO$^+$, and HCN, are concentrated in a northwest-southeast diagonal seen as a dark dust lane in HST images. Resolved clumps have masses between $\sim 200-2500$ \Msun, and the values obtained using the virial theorem are larger than the masses obtained through $^{12}$CO and $^{12}$CO luminosity. The velocity dispersion of the clumps is due both to self-gravity and the external pressure of the gas. Clumps at the center of our map, which have detections of dense gas tracers ($n_{crit}\sim10^6$ cm$^{-3}$ and above), are spatially coincident with young stellar objects. Conclusions: The clumps' physical and chemical properties are consistent with other clumps in 30 Dor. We suggest that these clumps are the densest regions of a Molecular Cloud carved by the radiation of R136.

astro-ph.GA↗

arXiv2025

PRODIGE - envelope to disk with NOEMA: V. Low 12C/13C ratios for CH3OH and CH3CN in hot corinos

The 12C/13C isotope ratio has been derived towards numerous cold clouds (20-50 K) and a couple protoplanetary disks and exoplanet atmospheres. However, direct measurements of this ratio in the warm gas (>100 K) around young low-mass protostars remain scarce, but are required to study its evolution during star and planet formation. We derived 12C/13C ratios from the isotopologues of the complex organic molecules (COMs) CH3OH and CH3CN in the warm gas towards seven Class 0/I protostellar systems to improve our understanding of the evolution of the 12C/13C ratios during star and planet formation. We used the data that were taken as part of the PRODIGE large program with the NOEMA at 1mm. The emission of CH3OH and CH3CN is spatially unresolved in the PRODIGE data (300au scale). Derived rotational temperatures exceed 100K, telling us that they trace the gas of the hot corino, where CH3CN probes hotter regions than CH3OH on average (290 K versus 180 K). The column density ratios between the 12C and 13C isotopologues, derived from LTE analysis, range from 4 to 30, thus, are significantly lower than the expected local ISM isotope ratio of about 68. Assuming that CH3CN and CH3OH may inherit the 12C/13C ratio from their precursor species, astrochemical models were conducted for the latter and compared with our observational results. We conclude that an enrichment in 13C in COMs at the earliest protostellar stages is likely inherited from the COMs' precursor species, whose 12C/13C ratios are set during the prestellar stage via isotopic exchange reactions. This also implies that low 12C/13C ratios observed at later evolutionary stages could at least partially be inherited. A final conclusion on 12C/13C ratios in protostellar environments requires improved observations to tackle current observational limitations and additional modelling efforts.

astro-ph.GA↗

arXiv2025

Resolved Gas Temperatures and 12C/13C ratios in SVS13A from ALMA Observations of CH3CN and CH3-13-CN

Context. Multiple systems are common in field stars, and the frequency is found to be higher in early evolutionary stages. Thus, the study of young multiple systems during the embedded stages is key to have a comprehensive understanding of star formation. In particular, how material accretes from the large-scale envelope into the inner region and how this flow interacts with the system physically and chemically has not yet been well characterized observationally. Aims. We aim to provide a snapshot of the forming protobinary system SVS13A, consisting of VLA4A and VLA4B. This includes clear pictures of its kinematic structures, physical conditions, and chemical properties. Methods. We conducted ALMA observations toward SVS13A targeting CH3CN and CH3-13CN J=12-11 K-ladder line emission with a high spatial resolution of ~30 au at a spectral resolution of ~0.08 km s-1 Results. We perform LTE radiative transfer models to fit the spectral features of the line emission. We find the two-layer LTE radiative model including dust absorption is essential to interpret the CH3CN and CH3-13-CN line emission. We identify two major and four small kinematic components, and derive their physical and chemical properties. Conclusions. We find a possible infalling signature toward the bursting secondary source VLA4A, which may be fed by an infalling streamer from the large-scale envelope. The mechanical heating in the binary system, as well as the infalling shocked gas, likely play a role in the thermal structure of the protobinary system. By accumulating mass from the streamer, the system might have experienced a gravitationally unstable phase before the accretion outburst. Finally, the derived CH3CN/CH3-13-CN ratio is lower than the canonical ratio in the ISM and is different between VLA4A and VLA4B.

astro-ph.GA↗

arXiv2024

PRODIGE -- envelope to disk with NOEMA. IV. An infalling gas bridge surrounding two Class 0/I systems in L1448N

Context. The formation of stars has been subject to extensive studies in the past decades from molecular cloud to protoplanetary disk scales. It is still not fully understood how the surrounding material in a protostellar system, that often shows asymmetric structures with complex kinematic properties, feeds the central protostar(s) and their disk(s). Aims. We study the spatial morphology and kinematic properties of the molecular gas surrounding the IRS3A and IRS3B protostellar systems in the L1448N region located in the Perseus molecular cloud. Methods. We present 1 mm NOEMA observations of the PRODIGE large program and analyze the kinematic properties of molecular lines. Given the complexity of the spectral profiles, the lines are fitted with up to three Gaussian velocity components. The clustering algorithm DBSCAN is used to disentangle the velocity components into the underlying physical structure. Results. We discover an extended gas bridge (~3000 au) surrounding both the IRS3A and IRS3B systems in six molecular line tracers (C18O, SO, DCN, H2CO, HC3N, and CH3OH). This gas bridge is oriented along the northeast-southwest direction and shows clear velocity gradients on the order of 100 km/s/pc towards the IRS3A system. We find that the observed velocity profile is consistent with analytical streamline models of gravitational infall towards IRS3A. The high-velocity C18O (2-1) emission towards IRS3A indicates a protostellar mass of ~1.2 Msun. Conclusions. While high angular resolution continuum data often show IRS3A and IRS3B in isolation, molecular gas observations reveal that these systems are still embedded within a large-scale mass reservoir with a complex spatial morphology as well as velocity profiles. The kinematic properties of the extended gas bridge are consistent with gravitational infall toward the IRS3A protostar.

astro-ph.GA↗

arXiv2024

PRODIGE -- Planet-forming disks in Taurus with NOEMA

We aim to constrain the gas density and temperature distributions as well as gas masses in several T Tauri protoplanetary disks located in Taurus. We use the 12CO, 13CO, and C18O (2-1) isotopologue emission observed at 0.9 with the IRAM NOrthern Extended Millimeter Array (NOEMA) as part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution PIs: P. Caselli & Th. Henning). Our sample consists of Class II disks with no evidence of strong radial substructures. We use thesedata to constrain the thermal and chemical structure of these disks through theoretical models for gas emission. To fit the combined optically thick and thin CO line data in Fourier space, we developed the DiskCheF code, which includes the parameterized disk physical structure, machine-learning (ML) accelerated chemistry, and the RADMC-3D line radiative transfer module. A key novelty of DiskCheF is the fast and feasible ML-based chemistry trained on the extended grid of the disk physical-chemical models precomputed with the ANDES2 code. This ML approach allows complex chemical kinetics models to be included in a time-consuming disk fitting without the need to run a chemical code. We present a novel approach to incorporate chemistry into disk modeling without the need to explicitly calculate a chemical network every time. Using this new disk modeling tool, we successfully fit the 12CO, 13CO, and C18O (2-1) data from the CI, CY, DL, DM, DN, and IQ Tau disks. The combination of optically thin and optically thick CO lines allows us to simultaneously constrain the disk temperature and mass distribution, and derive the CO-based gas masses. These values are in reasonable agreement with the disk dust masses rescaled by a factor of 100 as well as with other indirect gas measurements.

astro-ph.EP↗

arXiv2024

PRODIGE -- Envelope to Disk with NOEMA III. The origin of complex organic molecule emission in SVS13A

Complex Organic Molecules (COMs) have been found toward low-mass protostars but the origins of the COM emission are still unclear. It can be associated with, for example, hot corinos, outflows, and/or accretion shock/disk atmosphere. We have conducted NOEMA observations toward SVS13A from the PROtostars & DIsks: Global Evolution (PRODIGE) program. Our previous \ce{DCN} observations reveal a possible infalling streamer, which may affect the chemistry of the central protobinary by inducing accretion outbursts and/or shocked gas. Here, we further analyze six O-bearing COMs: CH3OH, aGg'-(CH2OH)2, C2H5OH, CH2(OH)CHO, CH3CHO, and CH3OCHO. Although the COM emission is not spatially resolved, we constrain the source sizes to $\lesssim0.3-0.4$ arcsec (90$-$120 au) by conducting uv-domain Gaussian fitting. Interestingly, the high-spectral resolution data reveal complex line profiles with multiple peaks showing differences between these six O-bearing COMs. The LTE fitting unveils differences in excitation temperatures and emitting areas among these COMs. We further conduct multiple-velocity-component LTE fitting to decompose the line emission into different kinematic components. Up to 6 velocity components are found from the LTE modeling. The temperature, column density, and source size of these components from each COM are obtained. We find a variety in excitation temperatures ($100-500$ K) and source sizes (D$\sim10-70$ au) from these kinematic components from different COMs. The emission of each COM can trace several components and different COMs most likely trace different regions. Given this complex structure, we suggest that the central region is inhomogeneous and unlikely to be heated by only protostellar radiation. We conclude that accretion shocks induced by the large-scale infalling streamer likely exist and contribute to the complexity of the COM emission.

astro-ph.GA↗

arXiv2024

PRODIGE -- Planet-forming disks in Taurus with NOEMA. I. Overview and first results for 12CO, 13CO, and C18O

We are performing a line survey of 8 planet-forming Class II disks in Taurus with the IRAM NOrthern Extended Millimeter Array (NOEMA), as a part of the MPG-IRAM Observatory Program PRODIGE (PROtostars and DIsks: Global Evolution; PIs: P. Caselli and Th. Henning). Compact and extended disks around T Tauri stars CI, CY, DG, DL, DM, DN, IQ Tau, and UZ Tau E are observed in ~80 lines from >20 C-, O,- N-, and S-bearing species. The observations in four spectral settings at 210-280 GHz with $1σ$ rms sensitivity of ~ 8-12 mJy/beam at 0.9" and 0.3 km/s resolution will be completed in 2024. The uv-visibilities are fitted with the DiskFit model to obtain key stellar and disk properties. In this paper, the combined $^{12}$CO, $^{13}$CO and C$^{18}$O $J = 2-1$ data are presented. We find that the CO fluxes and disk masses inferred from dust continuum tentatively correlate with the CO emission sizes. We constrain dynamical stellar masses, geometries, temperatures, the CO column densities and gas masses for each disk. The best-fit temperatures at 100 au are ~ 17-37 K, and decrease radially with the power-law exponent q ~ 0.05-0.76. The inferred CO column densities decrease radially with the power-law exponent p ~ 0.2-3.1. The gas masses estimated from $^{13}$CO (2-1) are ~ $0.001-0.2 M_\textrm{Sun}$. The best-fit CO column densities point to severe CO freeze-out in the disks. The DL Tau disk is an outlier, and has either stronger CO depletion or lower gas mass than the rest of the sample. The CO isotopologue ratios are roughly consistent with the observed values in disks and the low-mass star-forming regions.

astro-ph.GA↗

arXiv2023

Flow of gas detected from beyond the filaments to protostellar scales in Barnard 5

The infall of gas from outside natal cores has proven to feed protostars after the main accretion phase (Class 0). This changes our view of star formation to a picture that includes asymmetric accretion (streamers), and a larger role of the environment. However, the connection between streamers and the filaments that prevail in star-forming regions is unknown. We investigate the flow of material toward the filaments within Barnard 5 (B5) and the infall from the envelope to the protostellar disk of the embedded protostar B5-IRS1. Our goal is to follow the flow of material from the larger, dense core scale, to the protostellar disk scale. We present new HC$_3$N line data from the NOEMA and 30m telescopes covering the coherence zone of B5, together with ALMA H$_2$CO and C$^{18}$O maps toward the protostellar envelope. We fit multiple Gaussian components to the lines so as to decompose their individual physical components. We investigate the HC$_3$N velocity gradients to determine the direction of chemically-fresh gas flow. At envelope scales, we use a clustering algorithm to disentangle the different kinematic components within H$_2$CO emission. At dense core scales, HC$_3$N traces the infall from the B5 region toward the filaments. HC$_3$N velocity gradients are consistent with accretion toward the filament spines plus flow along them. We found a $\sim2800$ au streamer in H$_2$CO emission which is blueshifted with respect to the protostar and deposits gas at outer disk scales. The strongest velocity gradients at large scales curve toward the position of the streamer at small scales, suggesting a connection between both flows. Our analysis suggests that the gas can flow from the dense core to the protostar. This implies that the mass available for a protostar is not limited to its envelope, and can receiving chemically-unprocessed gas after the main accretion phase.

astro-ph.GA↗

arXiv2022

PRODIGE -- Envelope to Disk with NOEMA II. Small-scale temperature structure and a streamer feeding the SVS13A protobinary using CH3CN and DCN

Aims. We present high sensitivity and high-spectral resolution NOEMA observations of the Class 0/I binary system SVS13A, composed of the low-mass protostars VLA4A and VLA4B with a separation of ~90 au. VLA4A is undergoing an accretion burst that enriches the chemistry of the surrounding gas. This gives us an excellent opportunity to probe the chemical and physical conditions as well as the accretion process. Methods. We observe the (12K-11K) lines of CH3CN and CH313CN, the DCN (3-2) line, and the C18O (2-1) line toward SVS13A using NOEMA. Results. We find complex line profiles at disk scales which cannot be explained by a single component or pure Keplerian motion. By adopting two velocity components to model the complex line profiles, we find that the temperatures and densities are significantly different between these two components. This suggests that the physical conditions of the emitting gas traced via CH3CN can change dramatically within the circumbinary disk. In addition, combining our observations of DCN (3-2) with previous ALMA high-angular-resolution observations, we find that the binary system (or VLA4A) might be fed by an infalling streamer from envelope scales (~700 au). If this is the case, this streamer contributes to the accretion of material onto the system with a rate of at least 1.4x10-6 Msun yr-1. Conclusions. We conclude that the CH3CN emission in SVS13A traces hot gas from a complex structure. This complexity might be affected by a streamer that is possibly infalling and funneling material into the central region.

astro-ph.GA↗

arXiv2022

PRODIGE -- Envelope to disk with NOEMA I. A 3000 au streamer feeding a Class I protostar

Context. In the past few years, there has been a rise in the detection of streamers, asymmetric flows of material directed toward the protostellar disk with material from outside the star's natal core. It is unclear how they affect the process of mass accretion, in particular beyond the Class 0 phase. Aims. We investigate the gas kinematics around Per-emb-50, a Class I source in the crowded star-forming region NGC 1333. Our goal is to study how the mass infall proceeds from envelope to disk scales in this source. Results. We discover a streamer delivering material toward Per-emb-50 in H$_2$CO and C$^{18}$O emission. The streamer's emission can be well described by the analytic solutions for an infalling parcel of gas along a streamline with conserved angular momentum, both in the image plane and along the line of sight velocities. The streamer has a mean infall rate of $1.3 \times 10^{ -6}$ M$_{ \odot}$ yr$^{ -1}$, $5 -10$ times higher than the current accretion rate of the protostar. SO and SO$_2$ emission reveal asymmetric infall motions in the inner envelope, additional to the streamer around Per-emb-50. Furthermore, the presence of SO$_2$ could mark the impact zone of the infalling material. Conclusions. The streamer delivers sufficient mass to sustain the protostellar accretion rate and might produce an accretion burst, which would explain the protostar's high luminosity with respect to other Class I sources. Our results highlight the importance of late infall for protostellar evolution: streamers might provide a significant amount of mass for stellar accretion after the Class 0 phase.

astro-ph.GA↗

arXiv2020

ALMA resolves molecular clouds in the metal poor Magellanic Bridge A

(Abridged)We characterize gas and dust emission in Magellanic Bridge A, which has the highest 870$μ$m excess of emission found in single dish surveys. Using the ALMA telescope, we mapped the Magellanic Bridge A molecular cloud with sub-parsec resolution, in 1.3 mm continuum and CO(2-1) line emission. We also map the cloud in 870$μ$m continuum and CO(2-1) line emission at ~6 pc resolution with APEX. We combine the ALMA and APEX CO(2-1) line cubes to study the molecular gas emission. Magellanic Bridge A breaks up into two distinct molecular clouds in dust and CO(2-1) emission, which we call North and South. Dust emission in the North source, according to our best parameters from fitting the far-infrarred fluxes, is ~3 K colder than in the South source in correspondence to its less developed star formation. Both dust sources present large submillimeter excesses in LABOCA data: according to our best fits the excess over the modified blackbody (MBB) fit to the Spitzer/Herschel continuum are ~7 and ~3 for the North and South sources respectively. Nonetheless, we do not detect the corresponding 1.3 mm continuum with ALMA. Our limits are compatible with the extrapolation of the MBB fits and therefore we cannot independently confirm the excess at this longer wavelength. The CO(2-1) emission is in two parsec-sized clouds with virial masses around 400 and 700 Mo each. Their volume densities are ~700-2600 cm$^{-3}$, larger than typical bulk densities of Galactic molecular clouds. The CO-to-H2 conversion factor is 6.5 and 15 M$_{\odot}$ (K km s$^{-1}$ pc$^2$)$^{-1}$ for the North and South clouds, calculated using their respective virial masses and CO(2-1) luminosities. Gas mass estimates from our MBB fits to dust emission yields masses $M\sim1.3\times10^3$ M$_{\odot}$ and $2.9\times10^3$ M$_{\odot}$ for North and South respectively, a factor ~4 larger than the virial masses we infer from CO.

astro-ph.GA↗