arXiv subjects

Luca Moscadelli

Publications and source records attributed to Luca Moscadelli.

At least 19 recordsLinked to original sources

arXiv2025

Detections of Compact Radio Continuum toward Methanol Maser Rings Using the VLA

High-mass protostars are deeply embedded in dust inside their natal cores and are not easily detectable. However, maser emission at centimeter wavelengths, owing to its high brightness, enables us to study gas kinematics in protostars' circumstellar regions. We aim to understand the origin of the ring-like structures outlined by the 6.7 GHz methanol maser emission in six high-mass young stellar objects by performing a sensitive search of the associated radio-continuum emission and derive its properties. We used the Karl G. Jansky Very Large Array in the A configuration at C and K bands in order to image radio-continuum as well as 6.7 GHz methanol and 22 GHz water maser emission. We present the first images of the thermal jets towards four targets in our sample, G23.389+00.185, G23.657-00.127, G28.817+00.365, and G30.400-00.296. In a further target, G23.207-00.377, the complex K band continuum emission makes it unclear whether the detected peaks trace jet knots from a single young protostar or mark multiple compact young protostars. The remaining source G31.047+00.356 shows radio continuum emission associated with an evolved H II region.

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arXiv2025

ALMAGAL VII. Cataloging Hierarchical Mass Structure from Cores to Clumps across the Galactic Disk

Investigating the multi-scale fragmentation of dense clumps into compact cores is essential for understanding the processes that govern the initial distribution of mass in stellar clusters and how high-mass stars ($>8~M_{\odot}$) form. We present a catalog of the hierarchical continuum structure from 904 clumps observed in the ALMAGAL program, a high resolution ($0.15-0.8$\arcsec) 1.38 mm Atacama Large Millimeter/submillimeter Array (ALMA) large program targeting dense clumps capable of high-mass star formation throughout the Galactic disk. We use \verb|astrodendro|, a dendrogram-based algorithm, on a uniform linear resolution (2000 au) version of the data to extract 5160 continuum structures with effective radii spanning $800-42000$ au and estimated masses between $~0.05-670~M_{\odot}$. With our large sample, we statistically examine differences in clump properties for regions with varying levels of hierarchical complexity. We find that clumps exhibiting the richest hierarchical morphology have distributions with higher dust temperatures, surface densities, luminosity-to-mass (\textit{L/M}) ratios, and most massive core (MMC) masses, indicating that these regions tend to be at later evolutionary stages. We find a positive correlation between the mass of cores from the ALMAGAL core catalog and the surface density of their surrounding structures identified in this work. However, this correlation is weaker for cores in more evolved clumps, where lower mass cores can be found at higher local surface densities. This could indicate that some cores accrete mass less efficiently from the intra-clump reservoir than others, despite the total available mass increasing over time, a scenario that is congruent with a clump-fed core accretion model.

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arXiv2025

Protostellar Outflows at the EarliesT Stages (POETS). VIII. The jets in the intermediate-mass star-forming region G105.42+9.88 (alias LkH{\alpha} 234)

Our aim is to investigate the protostellar jets inside the young stellar object (YSO) cluster G105.42+9.88 (alias LkH$\alpha$ 234). This is one of the least luminous targets of the Protostellar Outflows at the EarliesT Stages (POETS) survey, which has been recently carried out to study young outflow emission on scales of 10-100 au. The combination of multi-epoch water maser very long baseline interferometry (VLBI) observations with sensitive Jansky Very Large Array (JVLA) continuum and Large Binocular Telescope (LBT) H$_2$ 2.12 $\mu$m observations, allows us to study the protostellar outflows from the intermediate-mass binary system VLA 3A and 3B, separated by ~0.22", and from VLA 2, an intermediate-mass YSO placed ~1" to northwest of VLA 3. Toward VLA 2, the 2001 and 2011 Very Long Baseline Array (VLBA) observations consistently show that the water masers are tracing a jet. The analysis of the 3D flow velocities proves that the jet is magneto-centrifugally launched in a magnetohydrodynamic (MHD) disk wind (DW). We infer launch radii in the range 10-50 au for the streamlines traced by the water masers. The global VLBI 2023 water maser observations indicate that the jet propagation can be hindered by a very dense clump placed northeast of VLA 2 and that is consistent with the large-scale LBT H$_2$ emission, tracing only the southwest lobe of the VLA 2 jet. Instead, the parallel jets emitted by the nearby YSOs VLA 3A and 3B can be reliably tracked with the H$_2$ emission at scales of a few 10" to both the southwest and the northeast. In particular, northeast of VLA 3 the direction of these two jets crosses a linear chain of spaced H$_2$ knots, which is a clear signature of an episodic jet. The variable ejection from VLA 3B, witnessed by the water masers at scales of ~10 au, could be the origin of the episodic jet observed at larger scales.

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arXiv2025

Protostellar Outflows at the EarliesT Stages (POETS). VII. Circumstellar gas kinematics traced by water masers inside the HC HII region NGC7538 IRS1

This article focuses on NGC7538 IRS1, one of the most luminous and studied HC HII regions in the northern hemisphere. Our aim is to identify the young stellar objects (YSOs) embedded within the ionized gas and study their kinematic structures. This work expands on a recent survey called "Protostellar Outflows at the EarliesT Stages" (POETS), which has been devoted to studying young outflow emission on scales of 10-100 au near luminous YSOs, before they start photoionizing the surrounding medium. We carried out multi-epoch Very Long Baseline Array observations of the 22 GHz water masers toward NGC7538 IRS1 to measure the maser 3D velocities, which, following POETS' findings, are reliable tracers of the protostellar winds. Recently, we reobserved the water masers in NGC7538 IRS1 with sensitive global very long baseline interferometry (VLBI) observations to map weaker maser emission. Our study confirms the presence of two embedded YSOs, IRS1a and IRS1b, at the center of the two linear distributions of 6.7 GHz methanol masers observed in the southern and northern cores of the HC HII region, which have been previously interpreted in terms of edge-on rotating disks. The water masers trace an extended (~200 au) stationary shock front adjacent to the inner portion of the disk around IRS1a. This shock front corresponds to the edge of the southern tip of the ionized core and might be produced by the interaction of the disk wind ejected from IRS1a with the infalling envelope. The water masers closer to IRS1b follow the same LSR velocity (Vlsr) pattern of the 6.7~GHz masers rotating in the disk, but the direction and amplitude of the water maser proper motions are inconsistent with rotation. We propose that these water masers are tracing a photo-evaporated disk wind, where the maser Vlsr traces mainly the disk rotation and the proper motions the poloidal velocity of the wind.

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arXiv2024

Protostellar Outflows at the EarliesT Stages (POETS) V. The launching mechanism of protostellar winds via water masers

Understanding the launching mechanism of winds and jets remains one of the fundamental challenges in astrophysics. The Protostellar Outflows at the EarliesT Stages (POETS) survey has recently mapped the 3D velocity field of the protostellar winds in a sample (37) of luminous young stellar objects (YSOs) at scales of 10-100 au via very long baseline interferometry (VLBI) observations of the 22 GHz water masers. In most of the targets, the distribution of the 3D maser velocities can be explained in terms of a magnetohydrodynamic (MHD) disk wind (DW). We have performed Very Long Baseline Array observations of the 22 GHz water masers in IRAS 21078+5211, the most promising MHD DW candidate from the POETS survey, to determine the 3D velocities of the gas flowing along several wind streamlines previously identified at a linear resolution of ~1 au. Near the YSO at small separations along ($xl \le 150$ au) and across ($R \le 40$ au) the jet axis, water masers trace three individual DW streamlines. By exploiting the 3D kinematic information of the masers, we determined the launch radii of these streamlines with an accuracy of $\sim$1 au, and they lie in the range of 10-50 au. At increasingly greater distances along the jet (110 au $\le xl \le 220$ au), the outflowing gas speeds up while it collimates close to the jet axis. Magneto-centrifugal launching in a radially extended MHD DW appears to be the only viable process to explain the fast (up to 60 km/s) and collimated (down to 10 degree) velocities of the wind in correspondence with launch radii ranging between 10 and 50 au. At larger separations from the jet axis ($R \ge 100$ au), the water masers trace a slow ($\le$20 km/s), radially expanding arched shock-front with kinematics inconsistent with magneto-centrifugal launching. Our resistive-magnetohydrodynamical simulations indicate that this shock-front could be driven by magnetic pressure.

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arXiv2023

The magnetic field of a magnetohydrodynamic disk wind: Water maser observations and simulations

Our goal is to measure and model the magnetic field distribution in the disk wind of the young stellar object (YSO) IRAS 21078+5211. We performed sensitive global Very Long Baseline Interferometry observations of the polarized emission of the 22 GHz water masers tracing individual streamlines of the magnetohydrodynamic (MHD) disk wind in IRAS 21078+5211. Our resistive-radiative-gravito-MHD simulations of a jet around a forming massive star are able to reproduce the maser kinematics in the inner jet cavity. We measure a weak level of 0.3%-3.2% of linear and circular polarization in 24 and 8 water masers, respectively. The detected polarized masers sample the direction and the strength of the magnetic field along five distinct streamlines within the inner 100 au region of the disk wind. Along the four streamlines at smaller radii from the jet axis (< 25 au), the sky-projected direction of the magnetic field forms, in most cases, a small offset angle of < 30$^{\circ}$ with the tangent to the streamline. Along the stream at larger radii (50-100 au), the magnetic field is sampled at only three separated positions, and it is found to be approximately perpendicular to the streamline tangent at heights of approximately 10 and 40 au, and parallel to the tangent at about 70 au. According to our simulations, the magnetic field lines should coincide with the flow streamlines in the inner jet cavity. The small tilt in the magnetic field direction observed along the inner streams can be well explained by Faraday rotation, assuming a realistic low level of ionization for the molecular shell of the jet of namely 10$^{-2}$. The magnetic field amplitudes measured from maser circular polarization are all within a relatively small range of 100-700 mG, which is in good agreement with the simulation results and consistent with reduced magnetic diffusivity in the jet cavity owing to efficient shock ionization.

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arXiv2022

Snapshot of a magnetohydrodynamic disk wind traced by water maser observations

The formation of astrophysical objects of different nature and size, from black holes to gaseous giant planets, involves a disk-jet system, where the disk drives the mass accretion onto a central compact object and the jet is a fast collimated ejection along the disk rotation axis. Magnetohydrodynamic disk winds can provide the link between mass accretion and ejection, which is essential to ensure that the excess angular momentum is removed from the system and accretion onto the central object can proceed. However, up to now, we have been lacking direct observational proof of disk winds. This work presents a direct view of the velocity field of a disk wind around a forming massive star. Achieving a very high spatial resolution of ~0.05 au, our water maser observations trace the velocities of individual streamlines emerging from the disk orbiting the forming star. We find that, at low elevation above the disk midplane, the flow co-rotates with its launch point in the disk, in agreement with magneto-centrifugal acceleration where the gas is flung away along the magnetic field line anchored to the disk. Beyond the co-rotation point, the flow rises spiraling around the disk rotation axis along a helical magnetic field. We have performed (resistive-radiative-gravito-) magnetohydrodynamic simulations of the formation of a massive star and record the development of a magneto-centrifugally launched jet presenting many properties in agreement with our observations.

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arXiv2022

Towards coordinated site monitoring and common strategies for mitigation of Radio Frequency Interference at the Italian radio telescopes

We present a project to implement a national common strategy for the mitigation of the steadily deteriorating Radio Frequency Interference (RFI) situation at the Italian radio telescopes. The project involves the Medicina, Noto, and Sardinia dish antennas and comprised the definition of a coordinated plan for site monitoring as well as the implementation of state-of-the-art hardware and software tools for RFI mitigation. Coordinated monitoring of frequency bands up to 40 GHz has been performed by means of continuous observations and dedicated measurement campaigns with fixed stations and mobile laboratories. Measurements were executed on the frequency bands allocated to the radio astronomy and space research service for shared or exclusive use and on the wider ones employed by the current and under-development receivers at the telescopes. Results of the monitoring campaigns provide a reference scenario useful to evaluate the evolution of the interference situation at the telescopes sites and a case series to test and improve the hardware and software tools we conceived to counteract radio frequency interference. We developed a multi-purpose digital backend for high spectral and time resolution observations over large bandwidths. Observational results demonstrate that the spectrometer robustness and sensitivity enable the efficient detection and analysis of interfering signals in radio astronomical data. A prototype off-line software tool for interference detection and flagging has been also implemented. This package is capable to handle the huge amount of data delivered by the most modern instrumentation on board of the Italian radio telecsopes, like dense focal plane arrays, and its modularity easen the integration of new algorithms and the re-usability in different contexts or telescopes.

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arXiv2022

Resolving the collimation zone of an intermediate-mass protostar

We report new VLA and e-MERLIN high resolution and sensitivity images of the Triple Radio continuum Source in the Serpens star forming region. These observations allowed us to perform a deep multi-frequency, multi-epoch study by exploring the innermost regions (<~100 au) of an intermediate-mass YSO for the first time, with a physical resolution of ~15 au. The kinematic analysis of knots recently ejected by the protostar indicates that the jet is undergoing episodic variations in velocity. In addition, our multi-frequency images reveal striking characteristics, e.g., a highly collimated ionized stream that would be launched at a radial distance of ~0.4 au from the protostar, and a narrow (~28 au wide) ionized cavity that would be excited by the interaction of a wide-angle component with the surrounding toroid of infalling material. In light of these results, we propose the scenario in which both a highly-collimated jet and a wide-angle wind coexist to be the most plausible to explain our observations, either launched by the X-wind or X- plus Disk-wind mechanism.

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arXiv2021

Zooming into the Collimation Zone in a Massive Protostellar Jet

Protostellar jets have a fundamental role at the earliest evolution of protostars of all masses. In the case of low-mass (<8 Msun) protostars, strong observational evidence exists that the launching and collimation is due to the X- and/or disk-wind mechanisms. In these models, it is the protostar/disk system that creates all the necessary conditions to launch and collimate the jets near the protostar via strong magnetic fields. The origin of jets from more massive protostars has been investigated much less, in part because of the difficulty of resolving the collimation zone in these more distant objects. Here we present the highest angular resolution observations of a jet powered by a massive protostar, the Cep A HW2 radio jet. We imaged the radio emission at projected distances of only ~20 au from the protostar, resolving the innermost 100 au of a massive protostellar jet for the first time. The morphology of the radio jet emission in this massive object is very different than what is usually observed in jets from low-mass protostars. We found that the outflowing material in HW2 has two components: a wide-angle wind launched from the protostar/disk system, and a highly collimated jet starting at 20-30 au from the protostar. We discuss two possible scenarios: an extension of the classical disk-wind to a massive protostar, or external collimation of a wide-angle wind. These results have important consequences for our understanding of how stars of different masses are formed.

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arXiv2021

The ionized heart of a molecular disk. ALMA observations of the hyper-compact HII region G24.78+0.08 A1

The study of hyper-compact (HC) or ultra-compact (UC) HII regions is fundamental to understanding the process of massive (> 8 M_sun) star formation. We employed Atacama Large Millimeter/submillimeter Array (ALMA) 1.4 mm Cycle 6 observations to investigate at high angular resolution (~0.050", corresponding to 330 au) the HC HII region inside molecular core A1 of the high-mass star-forming cluster G24.78+0.08. We used the H30alpha emission and different molecular lines of CH3CN and 13CH3CN to study the kinematics of the ionized and molecular gas, respectively. At the center of the HC HII region, at radii <~500 au, we observe two mutually perpendicular velocity gradients, which are directed along the axes at PA = 39 deg and PA = 133 deg, respectively. The velocity gradient directed along the axis at PA = 39 deg has an amplitude of 22 km/s mpc^(-1), which is much larger than the other's, 3 km/s mpc^(-1). We interpret these velocity gradients as rotation around, and expansion along, the axis at PA = 39 deg. We propose a scenario where the H30alpha line traces the ionized heart of a disk-jet system that drives the formation of the massive star (~20 M_sun) responsible for the HC HII region. Such a scenario is also supported by the position-velocity plots of the CH3CN and 13CH3CN lines along the axis at PA = 133 deg, which are consistent with Keplerian rotation around a 20 M_sun star. Toward the HC HII region in G24.78+0.08, the coexistence of mass infall (at radii of ~5000 au), an outer molecular disk (from <~4000 au to >~500 au), and an inner ionized disk (<~500 au) indicates that the massive ionizing star is still actively accreting from its parental molecular core. To our knowledge, this is the first example of a molecular disk around a high-mass forming star that, while becoming internally ionized after the onset of the HII region, continues to accrete mass onto the ionizing star.

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arXiv2021

Water maser variability in a high-mass YSO outburst -- VERA and ALMA observations of S255 NIRS 3

We carried out observations of the 22 GHz H2O masers in a high-mass protostar S255 NIRS 3 by using VERA. We measured the proper motions of the 22 GHz H2O masers associated with a bipolar outflow. The expansion velocity of the blueshifted bow shock traced by the 22 GHz H2O masers was 28 km s-1 corresponding to a dynamical timescale of 60 years. The direction of the maser outflow is slightly tilted compared with the radio jet, which could suggest a more recent ejection episode during the accretion burst event. The total flux density of the 22 GHz H2O masers has gradually increased from early 2017 and has become almost constant in 2018. For the first time, we reveal extended H2O maser emission at 22 GHz in a star forming region, which is partly resolved out by VERA and even by the most extended VLA configurations. We find that the flux variation of such an extended component is similar to that of the unresolved maser emission. We also conducted observations of the submillimeter continuum and the 321 GHz H2O masers with ALMA at Band 7. The continuum emission does not show significant variations compared with the previous observations performed 5 months before. We mapped the 321 GHz H2O masers in S255 NIRS 3 providing the fourth example, for this maser, of the spatial distribution in a high-mass star-forming region. The lower ratio of the 22 GHz/321 GHz maser luminosity in the blueshifted bow shock suggests a temperature (>1000 K), higher than for the other maser features in this region. We conclude that the bow shock structure traced by the 22 GHz H2O maser features is unlikely to be originating at the interface between the radio jet powered by the recent accretion outburst and the surrounding medium. The brightening of the 22 GHz H2O masers could be due to radiative excitation by photons form the infrared outburst escaping along the cavity created by the newly ejected material.

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arXiv2020

VLBI20-30: a scientific roadmap for the next decade -- The future of the European VLBI Network

This white paper describes the science case for Very Long Baseline Interferometry (VLBI) and provides suggestions towards upgrade paths for the European VLBI Network (EVN). The EVN is a distributed long-baseline radio interferometric array, that operates at the very forefront of astronomical research. Recent results, together with the new science possibilities outlined in this vision document, demonstrate the EVN's potential to generate new and exciting results that will transform our view of the cosmos. Together with e-MERLIN, the EVN provides a range of baseline lengths that permit unique studies of faint radio sources to be made over a wide range of spatial scales. The science cases are reviewed in six chapters that cover the following broad areas: cosmology, galaxy formation and evolution, innermost regions of active galactic nuclei, explosive phenomena and transients, stars and stellar masers in the Milky Way, celestial reference frames and space applications. The document concludes with identifying the synergies with other radio, as well as multi-band/multi-messenger instruments, and provide the recommendations for future improvements. The appendices briefly describe other radio VLBI arrays, the technological framework for EVN developments, and a selection of spectral lines of astrophysical interest below 100 GHz. The document includes a glossary for non-specialists, and a list of acronyms at the end.

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arXiv2020

The nature of the methanol maser ring G23.657$-$00.127. II. Expansion of the maser structure

Ring-like distributions of the 6.7 GHz methanol maser spots at milliarcsecond scales represent a family of molecular structures of unknown origin associated with high-mass young stellar objects (HMYSOs). We aim to study G23.657-00.127, which has a nearly circular ring of the 6.7 GHz methanol masers, and is the most suitable target to test hypotheses on the origin of the maser rings. The European Very Long Baseline Interferometry Network (EVN) was used at three epochs spanning 10.3 yr to derive the spatio-kinematical structure of the 6.7 GHz methanol maser emission in the target. The maser cloudlets, lying in a nearly symmetric ring, expand mainly in the radial direction with a mean velocity of 3.2 km s$^{-1}$. There is an indication that the radial component of the velocity increases with cloudlet's distance from the ring centre. The tangential component does not show any clear evidence for rotation of the cloudlets or any relationship with distance from the ring centre. The blue-shifted masers may hint at an anticlockwise rotation of cloudlets in the southern part of the ring. The nearly circular structure of the ring clearly persisted for more than 10 yr. Interferometric data demonstrated that about one quarter of cloudlets show significant variability in their brightness, although the overall spectrum was non-variable in single-dish studies. Taking into account the three-dimensional motion of the maser cloudlets and their spatial distribution along a small ring, we speculate about two possible scenarios where the methanol masers trace either a spherical outflow arising from an (almost) edge-on disc, or a wide angle wind at the base of a protostellar jet. The latter is associated with near- and mid-infrared emission detected towards the ring. High angular resolution images of complementary (thermal) tracers are needed to interpret the environment of methanol masers.

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arXiv2020

Protostellar Outflows at the EarliesT Stages (POETS). IV. Statistical properties of the 22 GHz H2O masers

We wish to perform a statistical study of the location and motion of individual 22 GHz water maser cloudlets, characterized by sizes that are within a few au, with respect to the radio thermal emission from young stellar objects (YSO). For this purpose, we have been carrying out the Protostellar Outflows at the EarliesT Stages (POETS) survey of a sample (38) of high-mass YSOs. The water maser positions and three-dimensional (3D) velocities were determined through Very Long Baseline Array observations with accuracies of a few milliarcsec (mas) and a few km/s, respectively. The position of the ionized core of the protostellar wind, marking the YSO, was determined through sensitive continuum Jansky Very Large Array observations with a typical error of 20 mas. The statistic of the separation of the water masers from the radio continuum shows that 84% of the masers are found within 1000 au from the YSO and 45% of them are within 200 au. Therefore, we can conclude that the 22 GHz water masers are a reliable proxy for the YSO position. The distribution of maser luminosity is strongly peaked towards low values, indicating that about half of the maser population is still undetected with the current Very Long Baseline Interferometry detection thresholds of 50-100 mJy/beam. Next-generation, sensitive radio interferometers will exploit these weak masers for an improved sampling of the velocity and magnetic fields around the YSOs. The average direction of the water maser proper motions provides a statistically-significant estimate for the orientation of the jet emitted by the YSO: 55% of the maser proper motions are directed on the sky within an angle of 30 deg from the jet axis. Finally, we show that our measurements of 3D maser velocities statistically support models in which water maser emission arises from planar shocks with propagation direction close to the plane of the sky.

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arXiv2019

Protostellar Outflows at the EarliesT Stages (POETS). III. H2O masers tracing disk-winds and jets near luminous YSOs

The goal of the Protostellar Outflows at the EarliesT Stages (POETS) survey is to image the disk-outflow interface on scales of 10-100 au in a statistically significant sample (36) of luminous young stellar objects (YSO), targeting both the molecular and ionized components of the outflows. The outflow kinematics is studied at milliarcsecond scales through VLBI observations of the 22 GHz water masers. We employed the JVLA at 6, 13, and 22 GHz in the A- and B-Array configurations to determine the spatial structure and the spectral index of the radio continuum emission. In about half of the targets, the water masers observed at separation <= 1000 au from the YSOs trace either or both of these kinematic structures: 1) a spatially elongated distribution oriented at close angle with the direction of collimation of the maser proper motions (PM), and 2) a linear LSR velocity (Vlsr) gradient across the YSO position. The kinematic structure (1) is readily interpreted in terms of a protostellar jet, as confirmed in some targets via the comparison with independent observations of the YSO jets, in thermal (continuum and line) emissions, reported in the literature. The kinematic structure (2) is interpreted in terms of a disk-wind (DW) seen almost edge-on on the basis of several pieces of evidence: first, it is invariably directed perpendicular to the YSO jet; second, it agrees in orientation and polarity with the Vlsr gradient in thermal emissions (when reported in the literature) identifying the YSO disk at scales of <= 1000~au; third, the PMs of the masers delineating the Vlsr gradients hint at flow motions at a speed of 10-20 km/s directed at large angles with the disk midplane. In the remaining targets, the maser PMs are not collimated but rather tend to align along two almost perpendicular directions, and could originate in DW-jet systems slightly inclined (<= 30 deg) with respect to edge-on.

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arXiv2019

A 10-$M_{\odot}$ YSO with a Keplerian disk and a nonthermal radio jet

We previously observed the star-forming region G16.59$-$0.05 through interferometric observations of both thermal and maser lines, and identified a high-mass young stellar object (YSO) which is surrounded by an accretion disk and drives a nonthermal radio jet. We performed high-angular-resolution (beam FWHM ~0.15") 1.2-mm continuum and line observations towards G16.59$-$0.05 with the Atacama Large Millimeter Array (ALMA). The main dust clump, with size ~10$^4$ au, is resolved into four relatively compact (diameter ~2000 au) millimeter (mm) sources. The source harboring the high-mass YSO is the most prominent in molecular emission. By fitting the emission profiles of several unblended and optically thin transitions of CH$_3$OCH$_3$ and CH$_3$OH, we derived gas temperatures inside the mm-sources in the range 42--131 K, and calculated masses of 1--5 $M_{\odot}$. A well-defined Local Standard of Rest velocity (Vlsr) gradient is detected in most of the high-density molecular tracers at the position of the high-mass YSO, pinpointed by compact 22-GHz free-free emission. This gradient is oriented along a direction forming a large (~70 degree) angle with the radio jet, traced by elongated 13-GHz continuum emission. The butterfly-like shapes of the P-V plots and the linear pattern of the emission peaks of the molecular lines at high velocity confirm that this Vlsr gradient is due to rotation of the gas in the disk surrounding the high-mass YSO. The disk radius is ~500 au, and the Vlsr distribution along the major axis of the disk is well reproduced by a Keplerian profile around a central mass of 10$\pm$2 $M_{\odot}$. The position of the YSO is offset by >~ 0.1" from the axis of the radio jet and the dust emission peak. To explain this displacement we argue that the high-mass YSO could have moved from the center of the parental mm source owing to dynamical interaction with one or more companions.

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arXiv2017

The Science Case for Simultaneous mm-Wavelength Receivers in Radio Astronomy

This review arose from the European Radio Astronomy Technical Forum (ERATec) meeting held in Firenze, October 2015, and aims to highlight the breadth and depth of the high-impact science that will be aided and assisted by the use of simultaneous mm-wavelength receivers. Recent results and opportunities are presented and discussed from the fields of: continuum VLBI (observations of weak sources, astrometry, observations of AGN cores in spectral index and Faraday rotation), spectral line VLBI (observations of evolved stars and massive star-forming regions) and time domain observations of the flux variations arising in the compact jets of X-ray binaries. Our survey brings together a large range of important science applications, which will greatly benefit from simultaneous observing at mm-wavelengths. Such facilities are essential to allow these applications to become more efficient, more sensitive and more scientifically robust. In some cases without simultaneous receivers the science goals are simply unachievable. Similar benefits would exist in many other high frequency astronomical fields of research.

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