VLA and NOEMA view of the Bok Globule CB 17: the starless nature of a proposed FHSC candidate

TL;DR

This study uses NOEMA and VLA observations to analyze the starless core CB 17 MMS, concluding it is not a First Hydrostatic Core candidate and revealing its physical and kinematic properties at high resolution.

Contribution

It provides high-resolution observations that disprove CB 17 MMS as a FHSC candidate and details its structure, dynamics, and evolutionary status.

Findings

No compact source detected at 1.3 mm position.

Core is consistent with a young starless core.

Velocity gradient suggests influence of nearby outflow.

Abstract

We use 3mm continuum NOEMA and NH$_3$ VLA observations towards the First Hydrostatic Core (FHSC) candidate CB 17 MMS to reveal the dust structure and gas properties down to 600-1,100 au scales and constrain its evolutionary stage. We do not detect any compact source at the previously identified 1.3 mm point source, despite expecting a minimum signal-to-noise of 9. The gas traced by NH$_3$ exhibits subsonic motions, with an average temperature of 10.4 K. A fit of the radial column density profile derived from the ammonia emission finds a flat inner region of radius $\sim$1,800 au and a central density of $\sim$6$\times10^5$ cm$^{-3}$. Virial and density structure analysis reveals the core is marginally bound ($\alpha_{vir}$= 0.73). The region is entirely consistent with a young starless core, hence ruling out CB 17 MMS as a FHSC candidate. Additionally, the core exhibits a velocity gradient aligned with the major axis, showing an arc-like structure in the p-v diagram and an off-center region with high-velocity dispersion caused by two distinct velocity peaks. These features could be due to interaction with the nearby outflow, which appears to deflect due to the dense gas near the NH$_3$ column density peak. We investigate the specific angular momentum profile of the starless core, finding that it aligns closely with previous studies of such radial profiles in Class 0 sources. This similarity to more evolved objects suggests that motions at 1,000 au scales are determined by large-scale dense cloud motions and may be preserved through the early stages of star formation.