2017A&A...602A..95L

Context. Triggered star formation around HII regions could be an important process. The Galactic HII region RCW 79 is a prototypical object for triggered high-mass star formation.
Aims. We aim to obtain a census of the young stellar population observed at the edges of the HII region and to determine the properties of the young sources in order to characterize the star formation processes that take place at the edges of this ionized region.
Methods. We take advantage of Herschel data from the surveys HOBYS, "Evolution of Interstellar Dust", and Hi-Gal to extract compact sources. We use the algorithm getsources. We complement the Herschel data with archival 2MASS, Spitzer, and WISE data to determine the physical parameters of the sources (e.g., envelope mass, dust temperature, and luminosity) by fitting the spectral energy distribution.
Results. We created the dust temperature and column density maps along with the column density probability distribution function (PDF) for the entire RCW 79 region. We obtained a sample of 50 compact sources in this region, 96% of which are situated in the ionization-compressed layer of cold and dense gas that is characterized by the column density PDF with a double-peaked lognormal distribution. The 50 sources have sizes of ∼0.1-0.4pc with a typical value of ∼0.2pc, temperatures of ∼11-26K, envelope masses of ∼6-760M_☉, densities of ∼0.1-44x10⁵cm^–3, and luminosities of ∼19-12712L_☉. The sources are classified into 16 class 0, 19 intermediate, and 15 class I objects. Their distribution follows the evolutionary tracks in the diagram of bolometric luminosity versus envelope mass (L_bol-M_env) well. A mass threshold of 140M_☉, determined from the L_bol-M_env diagram, yields 12 candidate massive dense cores that may form high-mass stars. The core formation efficiency (CFE) for the 8 massive condensations shows an increasing trend of the CFE with density. This suggests that the denser the condensation, the higher the fraction of its mass transformation into dense cores, as previously observed in other high-mass star-forming regions.