Characterizing the radio continuum nature of sources in the massive star-forming region W75N (B)

TL;DR

This study uses high-resolution radio observations to analyze the morphology and emission mechanisms of sources in W75N(B), revealing jet activity, signs of hyper-compact HII regions, and new embedded young stellar objects, advancing understanding of massive star formation.

Contribution

The paper provides the highest sensitivity and resolution radio data for W75N(B), identifying new sources and detailed emission characteristics of known protostars, including jets and hyper-compact HII regions.

Findings

VLA~1 drives a thermal radio jet and shows signs of a hyper-compact HII region.

VLA~3 also drives a thermal radio jet with associated shock-excited objects.

Three new weak radio sources likely represent embedded YSOs.

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 VLA data and ALMA archive data at 1.3 mm wavelength. We find that VLA~1 is driving a thermal radio jet at scales of $\approx$0.1 arcsec ($\approx$130 au), but also shows signs of an incipient hyper-compact HII region at scales of $\lesssim$ 1 arcsec ($\lesssim$ 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 HH objects), which show proper motions moving outward from VLA~3 at velocities of $\approx$112--118~km/s. We have also detected three new weak radio continuum sources, two of them associated with millimeter continuum cores observed with ALMA, suggesting that these two sources are also embedded YSOs in this massive star-forming region.