The G305 star-forming complex: a wide-area radio survey of ultra-compact HII regions

TL;DR

This study conducts a wide-area radio survey of the G305 star-forming complex, identifying and characterizing ultra-compact HII regions and other sources to understand massive star formation activity.

Contribution

It provides the first un-targeted, high-resolution radio survey of G305, detecting 71 sources and identifying six candidate UCHII regions with detailed physical properties.

Findings

Detected 71 compact radio sources in G305

Identified six candidate UCHII regions with specific physical parameters

Estimated a star formation rate of ~0.003 Msun yr^-1 in G305

Abstract

We present wide-area radio continuum 5.5 and 8.8 GHz (5.5 and 3.4 cm) Australia Telescope Compact Array observations of the complex and rich massive star-forming region G305. The aim of this study is to perform an un-targeted survey of the region in search of the compact radio emission associated with ultra-compact (UC) HII regions. Observations presented here encompass the entire complex and have a maximum resolution of ~1.5x1.4" and sensitivity of ~0.07 mJy beam^-1. By applying a data reduction method that emphasises small-scale structure, we are able to detect 71 compact radio sources distributed throughout the observed field. To explore the nature of these compact radio sources we compare to mid-infrared data and in this way identify 56 background sources, eight stellar radio sources, a single bright-rimmed cloud and six candidate UCHII regions. The physical properties of these candidate UCHII regions are determined and reveal five candidates have peak properties consistent with known UCHII regions with source radii ranging from 0.04-0.1 pc, emission measures from 2.56--10.3x10^-6 pc cm^-6 and electron densities of 0.34--1.03x10^4 cm^-3. We comment on these sites of recent massive star formation within G305 and by comparing to other star formation tracers (masers, NH3, YSOs) build a picture of the star formation history of the region. Using these results we estimate a lower limit to the star formation rate for the region of ~0.003 Msun yr^-1.