1 Aix Marseille Univ, CNRS, LAM, Laboratoire d’Astrophysique de Marseille, 10013 Marseille, France
2 National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, 100012 Beijing, PR China
3 University of Chinese Academy of Sciences, 100049 Beijing, PR China
4 Joint ALMA Observatory, 3107 Alonso de Cordova, Vitacura, Santiago, Chile
5 Univ. Bordeaux, LAB, CNRS, UMR 5804, 33270 Floirac, France
6 CNRS, LAB, UMR 5804, 33270 Floirac, France
7 I. Physik. Institut, University of Cologne, 50937 Cologne, Germany
8 Laboratoire AIM Paris-Saclay, CEA/DSM-CNRS-Université Paris Diderot, IRFU, Service d’Astrophysique, Centre d’Études de Saclay, Orme des Merisiers, 91191 Gif-sur-Yvette, France
9 Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Univ. Grenoble Alpes/CNRS-INSU, BP 53, 38041 Grenoble Cedex 9, France
10 Laboratoire AIM Paris-Saclay, CEA/IRFU-CNRS/INSU-Université Paris Diderot, Service d’Astrophysique, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
11 Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506, USA
12 Department of Astronomy, Peking University, 100871 Beijing, PR China
Received: 17 October 2016
Accepted: 24 January 2017
Context. Triggered star formation around H ii regions could be an important process. The Galactic H ii 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 H ii 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 ~ 0.1−0.4 pc with a typical value of ~ 0.2 pc, temperatures of ~ 11−26 K, envelope masses of ~ 6−760 M⊙, densities of ~ 0.1−44 × 105 cm-3, and luminosities of ~ 19−12 712 L⊙. 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 (Lbol−Menv) well. A mass threshold of 140 M⊙, determined from the Lbol−Menv 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.
Key words: HII regions / stars: formation / stars: massive / ISM: individual objects: RCW 79
Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
Final reduced data and maps used in the paper (FITS format) are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (18.104.22.168) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/602/A95
© ESO, 2017