Exploring the nature of compact radio sources associated to UCHII regions

TL;DR

This study uses 7 mm VLA observations to analyze compact radio sources in UCHII regions, identifying both thermal and non-thermal emissions and exploring their possible origins and evolutionary stages.

Contribution

First detailed 7 mm continuum observations of UCHII regions revealing the nature of associated compact radio sources, including thermal and non-thermal emissions.

Findings

Detected seven compact radio sources, four with thermal emission.

Identified two sources with non-thermal emission.

Thermal sources suggest ionized envelopes, static or flowing.

Abstract

We present Very Large Array 7 mm continuum observations of four Ultra-Compact (UC)HII regions, observed previously at 1.3 cm, in order to investigate the nature of the compact radio sources associated with these regions. We detected a total of seven compact radio sources, four of them with thermal emission, and two compact radio sources have clear non-thermal emission. The thermal emission is consistent with the presence of an ionized envelope, either static (i.e., trapped in the gravitational radius of an associated massive star) or flowing away (i.e., a photo-evaporative flow). On the other hand, the nature of the non-thermal sources remains unclear and several possibilities are proposed. The possibility that most of these compact radio sources are photo-evaporating objects and the remaining ones more-evolved objects is consistent with previous studies on UCHII regions.