Triggered massive-star formation on the borders of Galactic HII regions. II. Evidence for the collect and collapse process around RCW 79

TL;DR

This study provides observational evidence supporting the collect and collapse process as a mechanism for triggered massive-star formation at the borders of the Galactic HII region RCW 79, using multi-wavelength data.

Contribution

It presents detailed multi-wavelength observations of RCW 79, demonstrating the collect and collapse process as a trigger for massive-star formation.

Findings

Massive fragments form a dust ring around RCW 79

Presence of young stellar objects with IR excesses near fragments

Identification of Class I sources indicating recent star formation

Abstract

We present SEST-SIMBA 1.2-mm continuum maps and ESO-NTT SOFI JHK images of the Galactic HII region RCW 79. The millimetre continuum data reveal the presence of massive fragments located in a dust emission ring surrounding the ionized gas. The two most massive fragments are diametrically opposite each other in the ring. The near-IR data, centred on the compact HII region located at the south-eastern border of RCW 79, show the presence of an IR-bright cluster containing massive stars along with young stellar objects with near-IR excesses. A bright near- and mid-IR source is detected towards maser emissions, 1.2 pc north-east of the compact HII region centre. Additional information, extracted from the Spitzer GLIMPSE survey, are used to discuss the nature of the bright IR sources observed towards RCW 79. Twelve luminous Class I sources are identified towards the most massive millimetre fragments. All these facts strongly indicate that the massive-star formation observed at the border of the HII region RCW 79 has been triggered by its expansion, most probably by the collect and collapse process.