Triggered massive-star formation on the borders of Galactic H II regions

II. Evidence for the collect and collapse process around RCW 79

¹ Laboratoire d'Astrophysique de Marseille, 2 place Le Verrier, 13248 Marseille Cedex 4, France e-mail: annie.zavagno@oamp.fr
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
³ INAF-Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁴ INAF-Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125 Firenze, Italy

Received: 30 July 2005
Accepted: 7 September 2005

Abstract

We present SEST-SIMBA 1.2-mm continuum maps and ESO-NTT SOFI JHK_S images of the Galactic H ii 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 H ii 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 H ii region centre. Additional information extracted from the Spitzer GLIMPSE survey is 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 H ii region RCW 79 has been triggered by its expansion, most probably by the collect and collapse process.