Here we present deep (16 µJy beam −1 ), very high (40 mas) angular resolution 1.14 mm, polarimetric, Atacama Large Millimeter/submillimeter Array (ALMA) observations towards the massive protostar driving the HH 80-81 radio jet. The observations clearly resolve the disk oriented perpendicular to the radio jet, with a radius of 0. 171 (∼291 au at 1.7 kpc distance). The continuum brightness temperature, the intensity profile, and the polarization properties clearly indicate that the disk is optically thick for a radius of R 170 au. The linear polarization of the dust emission is detected almost all along the disk and its properties suggest that dust polarization is produced mainly by self-scattering. However, the polarization pattern presents a clear differentiation between the inner (optically thick) part of the disk and the outer (optically thin) region of the disk, with a sharp transition that occurs at a radius of ∼ 0. 1 (∼170 au). The polarization characteristics of the inner disk suggest that dust settling has not occurred yet with a maximum dust grain size between 50 and 500 µm. The outer part of the disk has a clear azimuthal pattern but with a significantly higher polarization fraction compared to the inner disk. This pattern is broadly consistent with self-scattering of a radiation field that is beamed radially outward, as expected in the optically thin outer region, although contribution from non-spherical grains aligned with respect to the radiative flux cannot be excluded.

Context. Most stars form in clusters, and thus it is important to characterize the protostellar disk population in dense environments to assess whether the environment plays a role in the subsequent evolution; specifically, whether planet formation is altered with respect to more isolated stars formed in dark clouds. Aims. Investigate the properties of the protostellar disks in the GGD 27 cluster and compare them with those obtained from disks formed in nearby regions. Methods. We used ALMA to observe the star-forming region GGD 27 at 1.14 mm with an unprecedented angular resolution, 40 mas (∼ 56 au) and sensitivity (∼ 0.002 M ⊙ ). Results.We detected a cluster of 25 continuum sources, most of which are likely tracing disks around Class 0/I protostars. Excluding the two most massive objects, disks masses are in the range 0.003-0.05 M ⊙ . The analysis of the cluster properties indicates that GGD 27 displays moderate subclustering. This result combined with the dynamical timescale of the radio jet (∼ 10 4 years) suggests the youthfulness of the cluster. The lack of disk mass segregation signatures may support this too. We found a clear paucity of disks with R disk > 100 au. The median value of the radius is 34 au, smaller than the median of 92 au for Taurus but comparable to the value found in Ophiuchus and in the Orion Nebula Cluster. In GGD 27 there is no evidence of a distance-dependent disk mass distribution (i. e., disk mass depletion due to external photoevaporation), most likely due to the cluster youth. There is a clear deficit of disks for distances < 0.02 pc. Only for distances > 0.04 pc stars can form larger and more massive disks, suggesting that dynamical interactions far from the cluster center are weaker, although the small disks found could be the result of disk truncation. This work demonstrates the potential to characterize disks from low-mass YSOs in distant and massive (still deeply embedded) clustered environments.

Recent high-angular resolution ( 40 mas) ALMA observations at 1.14 mm resolve a compact (R 200 au) flattened dust structure perpendicular to the HH 80-81 jet emanating from the GGD 27-MM1 high-mass protostar, making it a robust candidate for a true accretion disk. The jet/disk system (HH 80-81/GGD 27-MM1) resembles those found in association with low-and intermediate-mass protostars. We present radiative transfer models that fit the 1.14 mm ALMA dust image of this disk which allow us to obtain its physical parameters and predict its density and temperature structure.Our results indicate that this accretion disk is compact ( R disk 170 au) and massive ( 5 M ), about 20% of the stellar mass of 20 M . We estimate the total dynamical mass of the star-disk system from the molecular line emission finding a range between 21 and 30 M , which is consistent with our model. We fit the density and temperature structures found by our model with power law functions. These results suggest that accretion disks around massive stars are more massive and hotter than their low-mass siblings, but they still are quite stable. We also compare the temperature distribution in the GGD 27-MM1 disk with that found in low-and intermediate-mass stars and discuss possible implications on the water snow line. We have also carried out a study of the distance based on Gaia DR2 data and the population of young stellar objects (YSOs) in this region, and from the extinction maps. We conclude that the source distance is within 1.2 and 1.4 kpc, closer than what was derived in previous studies (1.7 kpc).

ABSTRACT The massive star-forming region W75N (B) is thought to host a cluster of massive protostars (VLA 1, VLA 2, and VLA 3) undergoing different evolutionary stages. In this work, we present radio continuum data with the highest sensitivity and angular resolution obtained to date in this region, using the VLA-A and covering a wide range of frequencies (4–48 GHz), which allowed us to study the morphology and the nature of the emission of the different radio continuum sources. We also performed complementary studies with multi-epoch Very Large Array (VLA) data and Atacama Large Millimeter Array (ALMA) archive data at 1.3 mm wavelength. We find that VLA 1 is driving a thermal radio jet at scales of ≈0.1 arcsec (≈130 au), but also shows signs of an incipient hypercompact H ii region at scales of ≲1 arcsec (≲1300 au). VLA 3 is also driving a thermal radio jet at scales of a few tenths of arcsec (few hundred of au). We conclude that this jet is shock exciting the radio continuum sources Bc and VLA 4 (obscured Herbig–Haro objects), which show proper motions moving outward from VLA 3 at velocities of ≈112–118 km s−1. We have also detected three new weak radio continuum sources, two of them associated with millimetre continuum cores observed with ALMA, suggesting that these two sources are also embedded young stellar objects in this massive star-forming region.