Triggered star formation on the borders of the Galactic H ii region RCW 120

Abstract

To investigate the process of star formation triggered by the expansion of an HII region, we present a multi-wavelength analysis of the Galactic HII region RCW 120 and its surroundings. The collect and collapse model predicts that the layer of gas and dust accumulated between the ionization and shock fronts during the expansion of the HII region collapses and forms dense fragments, giving rise to potential sites of massive-star formation. The aim of our study is to look for such massive fragments and massive young stars on the borders of RCW 120. We mapped the RCW 120 region in the cold dust continuum emission at 1.2 mm to search for these fragments. We supplemented this study with the available near- (2MASS) and mid-IR (GLIMPSE) data to locate the IR sources observed towards this region and to analyse their properties. We then compared the observational results with the predictions of Hosokawa & Inutsuka's model (2005, 2006). At 1.2 mm we detected eight fragments towards this region, five located on its borders. The largest fragment has a mass of about 370 Msun. Class I and Class II young stellar objects are detected all over the region, with some observed far from the ionization front. This result emphasises the possible importance distant interactions between the radiation, escaping from the ionized region, and the surrounding medium.