A VLA search for compact radio sources in the explosive molecular outflows DR 21 and G5.89

TL;DR

This study uses high-resolution VLA observations to identify compact radio sources in two explosive molecular outflows, aiming to find runaway stars and understand the origins of these energetic events.

Contribution

It provides the first high-resolution radio imaging of EMOs, identifying candidate runaway stars and refining the explosive event centers with arc structures.

Findings

13 compact radio sources detected in DR 21, with 3 likely magnetically active stars.

Arc structures suggest a common stellar origin for the EMOs and associated HII regions.

Limited detection of compact sources in G5.89 due to extended emission, but arc structures still trace ionizing sources.

Abstract

We present high-angular-resolution ($\sim0\rlap{.}''1$) VLA Ku-band (12--18 GHz) observations of two explosive molecular outflows (EMOs), DR 21 and G5.89, in a search for runaway stars related to these explosive events. In DR 21, we identified 13 compact radio sources (CRS), 9 located in the DR 21 core and near the CO streamer ejection region. The radio properties of the CRSs show that three are nonthermal radio emitters, likely magnetically active stars, while the nature of the remaining CRSs cannot be conclusively identified. All detected CRSs are good candidates for follow-up proper motion studies to confirm whether they are runaway stars. We also identify multiple ionized arc-shaped structures that can be fitted with parabolas whose symmetry axes converge to a position coincident with CRSs #11, raising the possibility that this source is the main ionizing star. A re-analysis of the 18 molecular outflow streamers refines the center of the explosive event, which aligns closely with the position indicated by the arcs convergence point, supporting a common stellar origin for the EMOs and the HII-region. In G5.89, the observations reveal a shell with a square-like morphology. The strong extended emission from this HII region prevents the detection of weak compact radio sources inside the shell; only two were identified well beyond the shell, and a single parabolic arc was fitted within this region. Overall, arc structures in ionized regions seem to be good tracers of the origin of the ionizing sources.