arXiv subjects

L. Moscadelli

Publications and source records attributed to L. Moscadelli.

At least 19 recordsLinked to original sources

arXiv2026

The CepA disk-outflow system at <=0.2'' or <=100au resolution

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 (~700pc) high-mass accretion disk candidates CepA HW2. Methods: Using the new long baseline array configuration (~1700m) of the Northern Extended Millimeter Array (NOEMA), we study CepA HW2 with a resolution of <=0.2'' or <=100au at 1.3mm in dust continuum and spectral line emission. Results: The mm continuum emission resolves the central disk candidate into several sub-structures. Conducting a Toomre Q stability analysis based on CH_3CN and continuum data, and a comparison to 3D radiation hydrodynamic simulations shows that the data are consistent with an almost edge-on disk where the observed sub-structures 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_3CN shows also 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 enforce the picture of high-mass star formation where multiplicity and fragmentation can happen on the smallest spatial scales related to the inner accretion disks.

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arXiv2026

Protostellar Outflows at the EarliesT Stages (POETS). IX. Magnetohydrodynamic disk winds traced by SO and SO$_2$ in luminous protostars

We investigate two massive young stellar objects (YSOs), IRAS21078+5211 and G035.02+0.35, where evidence for magnetohydrodynamic (MHD) disk winds (DWs) has been obtained at scales of 10-100 au through measurements of the 22GHz water maser velocity distribution within the Protostellar Outflows at the EarliesT Stages (POETS) survey. We employ IRAM Northern Extended Millimeter Array and archival Atacama Large Millimeter Array observations of IRAS21078+5211 and G035.02+0.35, respectively, to study kinematics and physical conditions of the corresponding protostellar winds on scales of 100-1000 au using the same molecular tracers. In IRAS21078+5211, the emissions of several molecules, particularly SO, SO2, CH3CN and CH3OH, are distributed along the axis of the radio jet, and present a LSR velocity (Vlsr) gradient transversal to the jet axis. Position-velocity (PV) plots of the SO lines show patterns consistent with Keplerian rotation. The SO2 emission comes from high velocity gas flowing close to the jet axis, while CH3CN and CH3OH present larger radial extension than the S-bearing species. In G035.02+0.35, the same molecules are instead distributed along the major axis of the rotating disk, and their Vlsr 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. 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 IRAS21078+5211, as well as the lack of molecules, except SO, in the G035.02+0.35's wind, can be explained in terms of a radially extended MHD DW, rather than a compact X-wind.

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arXiv2026

ALMAGAL IX. The chemical complexity of AG318.9477-00.1960: A line-identification template for ALMAGAL

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 \sim 10.4\,\rm kpc. We further assessed whether the emission of selected COMs, that is, ethylene glycol ((CH_2OH)_2; EG), glycolaldehyde (CH_2(OH)CHO; GA), and methyl formate (CH_3OCHO; MF), can be used to trace the innermost regions of hot molecular cores (HMCs). We analysed ALMA Band~6 observations (\sim 217-221GHz). Spectral line identification and local thermodynamic equilibrium modelling were performed using the software MADCUBA. We derived the physical parameters, including the column density (N), excitation temperature (Tex), 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 Tex maps and corresponding radial profiles.

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arXiv2026

ALMAGAL VIII. Early phases of triggered star formation in source AG286.0716$-$1.8229

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. We used the millimeter dust continuum data of the ALMAGAL survey and the Anderson et al. 2014 catalog of H II regions and selected one ALMAGAL source for ALMA follow-up observations. In fact, in source AG286.0716$-$1.8229 six cores were detected at a resolution of $\sim7600$ au, but only two at a higher resolution. The 4 cores not detected at higher resolution are prestellar core candidates. We used archival data from the SMGPS and RACS to confirm whether an H II region is present in the field. We observed the source with 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 estimates whether these cores are in an early phase of the star-formation process. The new Band 4 continuum image revealed three cores outside of the ALMAGAL field of view, for a total of 9 cores in the region, 8 of which are located along an arch of radius $\sim0.75$ pc. We have derived a spectral index between -0.14 and -0.4, in the frequency range of 0.8-1.6 GHz for the candidate H II region, which is consistent with optically thin free-free emission. Using plausible temperature ranges, based on the information from chemical tracers and the dust continuum, we derived mass ranges for the cores ($\sim2-16\,$M$_{\odot}$) and ranges for the virial parameter ($\sim0.3-5$). All the cores along the arch have virial parameters $\lesssim$2, with only one exception. 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.

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arXiv2025

Diverse stages of star formation in the IRAS 18162-2048 region. Emergence of UV Feedback

Methods: We obtained adaptive optics-assisted integral field spectroscopy in the near-infrared (IR) $K$ band ($1.93-2.47 \mathrm{\mu m}$) with VLT/SINFONI, complemented by VLA X and C bands (3$-$6 cm) and ALMA band 3 ($\sim$3.3 mm) observations. Results: The near-IR continuum reveals two infrared sources, IRS 2 and IRS 7, while the main protostellar core IRAS 18162-2048 remains undetected up to $2.47 \mathrm{\mu m}$. IRS 7 shows a peculiar Hydrogen Recombination Line Br$\gamma$ profile with a narrow emission component superimposed on a broad absorption feature, consistent with a B2/B3 zero-age main-sequence star. Extended H$_2$ emission exhibits a `sawtooth' pattern in the excitation diagram, characteristic of UV radiation in a PDR rather than shock excitation. The radiative transfer model Cloudy reproduces the H$_2$ ro-vibrational populations for $T_\mathrm{gas}=600$ K and $n_\mathrm{H}=7.9\times10^3 \mathrm{cm^{-3}}$. VLA X and C bands observations reveal a compact radio source previously reported as a stationary condensation (SC) and coincident with IRS 7. For the first time, we detect IRS 7/SC in mm wavelengths. The spectral index in the 3$-$6 cm and 3.3 mm regime is consistent with optically thin free-free emission. Conclusions: Our near-IR and radio observations reveal that IRS 7/SC is a B2/B3 ZAMS star that has begun to photoionise its environment, giving rise to an extended PDR and a compact \ion{H}{ii} region. The coexistence of this source with the deeply embedded protostar IRAS 18162-2048 and other bubble-like structures in the field, suggests a multigenerational star-forming environment. Future \textit{James Webb Space Telescope} observations targeting the H$_2$ pure rotational lines ($3-28 \mathrm{\mu m}$) and other HRLs less affected by extinction will be essential to characterise the cooler molecular and ionised gas to fully disclose the formation history of the region.

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arXiv2025

ALMAGAL VI. The spatial distribution of dense cores during the evolution of cluster-forming massive clump

High-mass stars and star clusters form from the fragmentation of massive dense clumps driven by gravity, turbulence, and magnetic fields. The ALMAGAL project observed $\sim1000$ clumps at $\sim$1000\,au resolution, enabling a statistically significant characterization of this process across a large range of clump physical parameters and evolutionary stages. In this work, we investigated the spatial distribution of dense cores in the 514 massive, potentially cluster-forming, clumps hosting at least 4 cores, to trace fragmentation's initial conditions and early evolution. We used quantitative descriptors, evaluated against the clump bolometric luminosity-to-mass ratio as an indicator of evolution. Core separations were measured with the minimum spanning tree method (MST) and compared with the Jeans gravitational fragmentation theory. We used the $Q$ parameter and the mass segregation ratio, $\Lambda_{MSR}$, to evaluate whether cores have specific arrangements or differences depending on their masses. ALMAGAL cores are usually arranged in elliptical groups with an axis ratio $e\sim2.2$, but $e\geq$5 is also observed. A single characteristic core separation per clump is found in $\sim76$% of cases, but signatures of multiple fragmentation lengths not rare. Typical core separations are compatible with the clump-averaged thermal Jeans length, $\lambda^{th}_{J}$, though a population, typical of low-fragmented/young clumps, has wider separations with $l\approx3\times\lambda^{th}_{J}$. The core separation decreases on average from $l\sim22000$ au in younger systems to $l\sim7000$ au in more evolved ones. Cores are typically distributed in fractal-type subclusters, with centrally concentrated patterns appearing only at later stages, but without a progressive evolutionary transition. Finally, mass segregation is found in 110 systems, with its occurrence increasing with evolution.

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arXiv2025

ALMAGAL V. Relations between the core populations and the parent clump physical properties

Context. The fragmentation of massive molecular clumps into smaller, potentially star-forming cores plays a key role in the processes of high-mass star formation. The ALMAGAL project offers high-resolution data to investigate these processes across various evolutionary stages in the Galactic plane. Aims. This study aims at correlating the fragmentation properties of massive clumps, obtained from ALMA observations, with their global physical parameters (e.g., mass, surface density, and temperature) and evolutionary indicators (such as luminosity-to-mass ratio and bolometric temperature) obtained from Herschel observations. It seeks to assess whether the cores evolve in number and mass in tandem with their host clumps, and to determine the possible factors influencing the formation of massive cores (M > 24M_\odot). Methods. We analyzed the masses of 6348 fragments, estimated from 1.4 mm continuum data for 1007 ALMAGAL clumps. Leveraging this unprecedentedly large data set, we evaluated statistical relationships between clump parameters, estimated over about 0.1 pc scales, and fragment properties, corresponding to scales of a few 1000 au, while accounting for potential biases related to distance and observational resolution. Our results were further compared with predictions from numerical simulations. Results. The fragmentation level correlates preferentially with clump surface density, supporting a scenario of density-driven fragmentation, whereas it does not show any clear dependence on total clump mass. Both the mass of the most massive core and the core formation efficiency show a broad range and increase on average by an order of magnitude in the intervals spanned by evolutionary indicators such as clump dust temperature and the luminosity-to-mass ratio. This suggests that core growth continues throughout the clump evolution, favoring clump-fed over core-fed theoretical scenarios.

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arXiv2025

ALMAGAL IV. Morphological comparison of molecular and thermal dust emission using the histogram of oriented gradients (HOG) method

The study of molecular line emission is crucial to unveil the kinematics and the physical conditions of gas in star-forming regions. Our aim is to quantify the reliability of using individual molecular transitions to derive physical properties of the bulk of the H2 gas, looking at morphological correlations in their overall integrated molecular line emission with the cold dust. For this study we selected transitions of H2CO, CH$_3$OH, DCN, HC$_3$N, CH$_3$CN, CH$_3$OCHO, SO, and SiO and compared them with the 1.38 mm dust continuum emission at different spatial scales in the ALMAGAL sample, that observed a total of 1013 targets covering all evolutionary stages of the high-mass star-formation process and different conditions of clump fragmentation. We used the method of the histogram of oriented gradients (HOG) implemented in the tool astroHOG to compare the morphology of integrated line emission with maps of the 1.38 mm dust continuum emission. Moreover, we calculated the Spearman's correlation coefficient, and compared it with our astroHOG results. Only H$_2$CO, CH$_3$OH, and SO show emission on spatial scales comparable with the diffuse continuum emission. However, from the HOG method, the median correlation of the emission of each of these species with the continuum is only $\sim$24-29%. In comparison with the dense fragments these molecular species still have low values of correlation. On the other hand DCN, HC$_3$N, CH$_3$CN, and CH$_3$OCHO show a good correlation with the dense dust fragments, above 60%. The worst correlation is seen with SiO, both with the extended continuum emission and with compact sources. From the comparison of the results of the HOG method and the Spearman's correlation coefficient, the HOG method gives much more reliable results than the intensity-based coefficient in estimating the level of similarity of the emission morphology.

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arXiv2025

A multi-scale view of the magnetic field morphology in the hot molecular core G31.41+0.31

Multiscale studies of the morphology and strength of the magnetic field are crucial to properly unveil its role and relative importance in high-mass star and cluster formation. G31.41+0.31 (G31) is a hub-filament system that hosts a high-mass protocluster embedded in a hot molecular core (HMC). G31 is one of the few sources showing a clear hourglass morphology of the magnetic field on scales between 1000 au and a few 100 au in previous interferometric observations. This strongly suggests a field-regulated collapse. To complete the study of the magnetic field properties in this high-mass star-forming region, we carried out observations with the James Clerk Maxwell Telescope $850 \mu$m of the polarized dust emission. These observations had a spatial resolution of $\sim$0.2 pc at 3.75 kpc. The aim was to study the magnetic field in the whole cloud and to compare the magnetic field orientation toward the HMC from $\sim$50,000 au to $\sim$260 au scales. The large-scale ($\sim$5 pc) orientation of the magnetic field toward the position of the HMC is consistent with that observed at the core ($\sim$4,000 au) and circumstellar ($\sim$260 au) scales. The self-similarity of the magnetic field orientation at these different scales might arise from the brightest sources in the protocluster, whose collapse is dragging the magnetic field. These sources dominate the gravitational potential and the collapse in the HMC. The cloud-scale magnetic field strength of the G31 hub-filament system, which we estimated using the Davis-Chandrasekhar-Fermi method, is in the range 0.04--0.09 mG. The magnetic field orientation in the star-forming region shows a bimodal distribution, and it changes from an NW--SE direction in the north to an E--W direction in the south [abridged abstract].

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arXiv2025

ALMAGAL I. The ALMA evolutionary study of high-mass protocluster formation in the Galaxy. Presentation of the survey and early results

Fundamental questions about the physics responsible for fragmenting molecular parsec-scale clumps into cores of ~1000 au are still open, that only a statistically significant investigation with ALMA is able to address: what are the dominant agents that determine the core demographics, mass, and spatial distribution as a function of the physical properties of the hosting clumps, their evolutionary stage and the different Galactic environments in which they reside? To what extent extent is fragmentation driven by clumps dynamics or mass transport in filaments? With ALMAGAL we observed the 1.38 mm continuum and lines toward more than 1000 dense clumps in our Galaxy, with M>500M_sun, surface density > 0.1 g/cm2 and d<7.5 kpc. The ACA and two 12-m array setups were used to deliver a minimum resolution of ~1000 au over the entire sample distance range. The sample covers all evolutionary stages from infrared dark clouds (IRDCs) to HII regions from the tip of the Galactic bar to the outskirts of the Galaxy. The spectral setup includes several molecular lines to trace the multiscale physics and dynamics of gas, notably CH3CN, H2CO, SiO, CH3OH, DCN, HC3N, SO etc. We present an initial overview of the observations and the early science product and results, with a first characterization of the morphological properties of the continuum emission. We use "perimeter-versus-area" and convex hull-versus-area metrics to classify the different morphologies. More extended and morphologically complex shapes are found toward clumps that are relatively more evolved and have higher surface densities.

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arXiv2025

ALMAGAL II. The ALMA evolutionary study of high-mass protocluster formation in the Galaxy. ALMA data processing and pipeline

The ALMAGAL Large Program has observed 1017 high-mass star-forming regions distributed throughout the Galaxy, sampling different evolutionary stages and environmental conditions. In this work, we present the acquisition and processing of the ALMAGAL data. The main goal is to set up a robust pipeline that generates science-ready products, with a good and uniform quality across the whole sample. ALMAGAL observations were performed with the Atacama Large Millimeter/submillimeter Array (ALMA). Each field was observed in three different telescope arrays, being sensitive to spatial scales ranging from 1000 au up to 0.1 pc. The spectral setup allows sensitive imaging of the continuum emission at 219 GHz, and it covers multiple molecular spectral lines observed in four different spectral windows that span about 4 GHz in frequency coverage. We have designed a Python-based processing workflow to calibrate and image these observational data. This ALMAGAL pipeline includes an improved continuum determination, suited for line-rich sources; an automatic self-calibration process that improves the dynamical range of the final images; and the combination of data from different telescope arrays to produce science-ready, fully combined images. The fully combined products have spatial resolutions in the range 800-2000 au, and mass sensitivities in the range 0.02-0.07 Mo. We also present a first analysis of the spectral line information included in the ALMAGAL setup, and its potential for future scientific studies. As an example, specific spectral lines at 1000 au scales resolve the presence of multiple outflows in clusters and will help us to search for disk candidates around massive protostars. Moreover, the broad frequency bands provide information on the chemical richness of the different cluster members, which can be used to study the chemical evolution during the formation process of star clusters.

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arXiv2025

ALMAGAL III. Compact source catalog: Fragmentation statistics and physical evolution of the core population

The mechanisms behind the fragmentation of high-mass dense clumps into compact star-forming cores are fundamental topics in current astrophysical research. The ALMAGAL survey provides the opportunity to study this process at an unprecedented level of detail and statistical significance, featuring high-angular resolution $1.38$ mm ALMA observations of $1013$ massive dense clumps at various Galactic locations. These clumps cover a wide range of distances, masses, surface densities, and evolutionary stages. Here, we present the catalog of compact sources obtained with the CuTEx algorithm from continuum images of the full ALMAGAL clump sample combining ACA-$7$m and $12$m ALMA arrays, reaching a uniform high median spatial resolution of $\sim1400$ au. We discuss the fragmentation properties and the estimated physical parameters of the core population. The ALMAGAL compact source catalog includes $6348$ cores detected in $844$ clumps ($83\%$ of the total), with a number of cores per clump between $1$ and $49$ (median of $5$). The estimated core diameters are mostly within $\sim800-3000$ au (median of $1700$ au). We obtained core masses from $0.002$ to $345\,\mathrm{M_{\odot}}$. We evaluated the variation in the core mass function (CMF) with evolution as traced by the clump $L/M$, finding a clear, robust shift and change in slope among CMFs within subsamples at different stages. This finding suggests that the CMF shape is not constant throughout the star formation process, but rather it builds (and flattens) with evolution, with higher core masses reached at later stages. We found that all cores within a clump grow in mass on average with evolution, and the number of cores increases with the core masses. Our results favor a clump-fed scenario for high-mass star formation, in which cores form as low-mass seeds, and then gain mass while further fragmentation occurs in the clump.

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arXiv2025

Gas infall via accretion disk feeding Cepheus A HW2

The star-forming region Cepheus A hosts a very young star, called HW2, that is the second closest to us growing a dozen times more massive than our Sun. The circumstellar environment surrounding HW2 has long been the subject of much debate about the presence or not of an accretion disk, whose existence is at the basis of our current paradigm of star formation. Here, we answer this long standing question by resolving the gaseous disk component, and its kinematics, through sensitive observations at cm wavelengths of hot ammonia (NH$_3$) with the Jansky Very Large Array. We map the accretion disk surrounding HW2 at radii between 200 and 700 au, showing how fast circumstellar gas collapses and slowly orbits to pile up near the young star at very high rates of $2\times10^{-3}$ M$_{\odot}$ yr$^{-1}$. These results, corroborated by state-of-the-art simulations, show that an accretion disk is still efficient in focusing huge mass infall rates near the young star, even when this star has already reached a large mass of 16 M$_{\odot}$.

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arXiv2025

Protostellar Outflows at the EarliesT Stages (POETS) VI. Evidence of disk-wind in G11.92-0.61 MM1

Magnetohydrodynamic disk-winds play a key role in the formation of massive stars by providing the fine-tuning between accretion and ejection, where excess angular momentum is redirected away from the disk, allowing further mass growth. However, only a limited number of disk-wind sources have been detected to date. To better constrain the exact mechanism of this phenomenon, expanding the sample is critical. We performed an analysis of the disk-wind candidate G11.92-0.61 MM1 by estimating the physical parameters of the system and constraining the wind-launching mechanism. Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 observations were conducted in September 2021 with ALMA's longest baselines, which provided a synthesised beam of $\sim$30 mas. We obtained high-resolution images of the CH$_3$CN ($v_8=1$ and $v=0$), CH$_3$OH, SO$_2$, and SO molecular lines, and the 1.3 mm continuum. Our molecular data allowed us to refine the parameters of the disk-outflow system in MM1. The rotating disk is resolved into two regions with distinct kinematics: the inner region ($<$300 au) is traced by high-velocity emission of high-excitation CH$_3$CN lines and shows a Keplerian rotation; the outer region ($>$300 au), traced by mid-velocity CH$_3$CN emission, rotates in a sub-Keplerian regime. The central source is estimated to be $\sim$20 $M_{\odot}$, which is about half the mass estimated in previous lower-resolution studies. A strong collimated outflow is traced by SO and SO$_2$ emission up to $\sim$3400 au around MM1a. The SO and SO$_2$ emissions show a rotation-dominated velocity pattern, a constant specific angular momentum, and a Keplerian profile that suggests a magneto-centrifugal disk-wind origin with launching radii of $\sim$50-100 au. G11.92-0.61 MM1 appears to be one of the clearest cases of molecular line-traced disk-winds detected around massive protostars.

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arXiv2024

Dynamical Accretion Flows -- ALMAGAL: Flows along filamentary structures in high-mass star-forming clusters

We use data from the ALMA Evolutionary Study of High Mass Protocluster Formation in the Galaxy (ALMAGAL) survey to study 100 ALMAGAL regions at $\sim$ 1 arsecond resolution located between $\sim$ 2 and 6 kpc distance. Using ALMAGAL $\sim$ 1.3mm line and continuum data we estimate flow rates onto individual cores. We focus specifically on flow rates along filamentary structures associated with these cores. Our primary analysis is centered around position velocity cuts in H$_2$CO (3$_{0,3}$ - 2$_{0,2}$) which allow us to measure the velocity fields, surrounding these cores. Combining this work with column density estimates we derive the flow rates along the extended filamentary structures associated with cores in these regions. We select a sample of 100 ALMAGAL regions covering four evolutionary stages from quiescent to protostellar, Young Stellar Objects (YSOs), and HII regions (25 each). Using dendrogram and line analysis, we identify a final sample of 182 cores in 87 regions. In this paper, we present 728 flow rates for our sample (4 per core), analysed in the context of evolutionary stage, distance from the core, and core mass. On average, for the whole sample, we derive flow rates on the order of $\sim$10$^{-4}$ M$_{sun}$yr$^{-1}$ with estimated uncertainties of $\pm$50%. We see increasing differences in the values among evolutionary stages, most notably between the less evolved (quiescent/protostellar) and more evolved (YSO/HII region) sources. We also see an increasing trend as we move further away from the centre of these cores. We also find a clear relationship between the flow rates and core masses $\sim$M$^{2/3}$ which is in line with the result expected from the tidal-lobe accretion mechanism. Overall, we see increasing trends in the relationships between the flow rate and the three investigated parameters; evolutionary stage, distance from the core, and core mass.

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arXiv2024

On the Structure of the Sagittarius Spiral Arm in the Inner Milky Way

We report measurements of trigonometric parallax and proper motion for two 6.7 GHz methanol and two 22 GHz water masers located in the far portion of the Sagittarius spiral arm as part of the BeSSeL Survey. Distances for these sources are estimated from parallax measurements combined with 3-dimensional kinematic distances. The distances of G033.64$-$00.22, G035.57$-$00.03, G041.15$-$00.20, and G043.89$-$00.78 are $9.9\pm0.5$, $10.2\pm0.6$, $7.6\pm0.5$, and $7.5\pm0.3$ kpc, respectively. Based on these measurements, we suggest that the Sagittarius arm segment beyond about 8 kpc from the Sun in the first Galactic quadrant should be adjusted radially outward relative to previous models. This supports the suggestion of Xu et al. (2023) that the Sagittarius and Perseus spiral arms might merge in the first quadrant before spiraling inward to the far end of the Galactic bar.

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arXiv2024

Self-similarity of the magnetic field at different scales: the case of G31.41+0.31

Context. Dust polarization observations of the massive protocluster G31.41+0.31 carried out at ~1'' (~3750 au) resolution with the SMA at 870 microm have revealed one of the clearest examples to date of an hourglass-shaped magnetic field morphology in the high-massregime. Additionally, ~0.24'' (~900 au) resolution observations with ALMA at 1.3 mm have confirmed these results. The next step is to investigate whether the magnetic field maintains its hourglass-shaped morphology down to circumstellar scales. Aims. To study the magnetic field morphology toward the four (proto)stars A, B, C, and D contained in G31.41+0.31 and examine whether the self-similarity observed at core scales (1'' and 0.24'' resolution) still holds at circumstellar scales, we carried out ALMA observations of the polarized dust continuum emission at 1.3 mm and 3.1 mm at an angular resolution of ~0.068'' (~250 au), sufficient to resolve the envelope emission of the embedded protostars. Methods. We used ALMA to perform full polarization observations at 233 GHz (Band 6) and 97.5 GHz (Band 3) with a synthesized beam of 0.072'' x 0.064''. We carried out polarization observations at two different wavelengths to confirm that the polarization traces magnetically aligned dust grains and is not due to dust self-scattering. Results. The polarized emission and the direction of the magnetic field obtained at the two wavelengths are basically the same, except for an area between the embedded sources C and B. In such an area, the emission at 1.3 mm could be optically thick and affected by dichroic extinction. ...

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arXiv2024

Proper motion study of the 6.7 GHz methanol maser rings. I. A sample of sources with little variation

Methanol masers at 6.7~GHz are well-known signposts of high-mass star-forming regions. [...] We aim to understand the origin of the ring-like structures outlined by methanol maser emission in a number of sources. This emission could be, a priori, spatially associated with an outflow and/or disc around a high-mass protostar. [...] Using sensitive, three-epoch observations spanning over eight years with the European VLBI Network, we have started the most direct investigations of maser rings using very accurate proper motion measurements with uncertainties below 1\,km~s$^{-1}$. We present full results for the five targets of our sample, G23.207-00.377, G23.389+00.185, G28.817+00.365, G31.047+00.356, and G31.581+00.077, where proper motions show similar characteristics; maser cloudlets do not move inwards towards the centre of the rings but rather outwards. We also include the most circular source, G23.657-00.127, in the discussion as a reference. The magnitude of maser proper motions ranges from a maximum of about 13\,km~s$^{-1}$ to 0.5~km~s$^{-1}$. In two of the five sources with a high number of maser spots (>100), namely G23.207-00.377 and G23.389+00.185, we show that the size of the best elliptical model, fitted to the distribution of persistent masers, increases in time in a manner similar to the case of G23.657-00.127. Moreover, we checked the separations between the pairs of spots from distinct regions, and we were able to assess that G28.817+00.365 and G31.047+00.356 can be interpreted as showing expanding motions. We analysed the profiles of single maser cloudlets and studied their variability. Contrary to single-dish studies, the interferometric data indicate variability of the emission of single-masing cloudlets. In five of the six targets expansion motions prevail. Only in the case of G31.581+00.077 can a scenario of disc-like rotation not be excluded. [...]

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