Protostellar cores in Sagittarius B2 N and M

TL;DR

This study uses high-resolution ALMA observations to analyze protostellar cores in Sagittarius B2, revealing fragmentation, properties of young stellar objects, and star formation rates in this active galactic region.

Contribution

The paper provides the first high-resolution (500-700 AU) ALMA imaging of protostellar cores in Sgr B2, detailing fragmentation and properties of Stage 0/I YSOs in this star-forming cloud.

Findings

Detected 371 sources at 3 mm and 218 at 1 mm, significantly increasing known protostellar objects.

Found that sources fragment into an average of two objects, with about a third showing fragmentation.

Estimated star formation rates of 0.0038 and 0.0093 solar masses per year for Sgr B2 N and M.

Abstract

We present 500 AU and 700 AU resolution 1 mm and 3 mm ALMA observations, respectively, of protostellar cores in protoclusters Sagittarius B2 (Sgr B2) North (N) and Main (M), parts of the most actively star-forming cloud in our Galaxy. Previous lower resolution (5000 AU) 3 mm observations of this region detected $\sim$150 sources inferred to be young stellar objects (YSOs) with $M>8\mathrm{\,M}_\odot$. With a tenfold increase in resolution, we detect 371 sources at 3 mm and 218 sources in the smaller field of view at 1 mm. The sources seen at low resolution are observed to fragment into an average of two objects. About a third of the observed sources fragment. Most of the sources we report are marginally resolved and are at least partially optically thick. We determine that the observed sources are most consistent with Stage 0/I YSOs, i.e., rotationally supported disks with an active protostar and an envelope, that are warmer than those observed in the solar neighborhood. We report source-counting-based inferred stellar mass and the star formation rate of the cloud: 2800$\mathrm{\,M}_\odot$, 0.0038$\mathrm{\,M}_\odot$ yr$^{-1}$ for Sgr B2 N and 6900$\mathrm{\,M}_\odot$, 0.0093$\mathrm{\,M}_\odot$ yr$^{-1}$ for Sgr B2 M respectively.