The Herschel view of the on-going star formation in the Vela-C molecular cloud⋆
1 INAF – Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
2 INAF – Istituto di Astrofisica e Planetologia Spaziale, via Fosso del Cavaliere 100, 00133 Rome, Italy
3 Laboratoire AIM, CEA/IRFU CNRS/INSU Université Paris Diderot, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
4 Université de Bordeaux, OASU, Bordeaux, France
5 University of Victoria, Department of Physics and Astronomy, PO Box 3055, STN CSC, Victoria, BC, V8W 3P6, Canada
6 National Research Council of Canada, Herzberg Institute of Astrophysics, 5071 West Saanich Rd., Victoria, BC, V9E 2E7, Canada
7 School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF243 AA, UK
8 Laboratoire AIM Paris-Saclay, CEA/IRFU – CNRS/INSU – Université Paris Diderot, Service d’Astrophysique, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
9 ESO, Karl Schwarzschild str. 2, 85748 Garching bei Munchen, Germany
10 School of Physics and Astronomy, Cardiff University, Queens Buildings, The Parade, Cardiff, CF243AA, UK
11 Department of Physics and Astronomy, The Open University, Milton Keynes, UK
12 Department of Physics and Astronomy, McMaster University, Hamilton, ON, L8S 4M1, Canada
Received: 2 August 2011
Accepted: 30 January 2012
Aims. As part of the Herschel guaranteed time key programme “HOBYS”, we present the PACS and SPIRE photometric survey of the star-forming region Vela-C, one of the nearest sites of low-to-high-mass star formation in the Galactic plane. Our main objectives are to take a census of the cold sources and to derive their mass distribution down to a few solar masses.
Methods. Vela-C was observed with PACS and SPIRE in parallel mode at five wavelengths between 70 μm and 500 μm over an area of about 3 square degrees. A photometric catalogue was extracted from the detections in each of the five bands, using a threshold of 5σ over the local background. Out of this catalogue we selected a robust sub-sample of 268 sources, of which ~75% are cloud clumps (diameter between 0.05 pc and 0.13 pc) and 25% are cores (diameter between 0.025 pc and 0.05 pc). Their spectral energy distributions (SEDs) were fitted with a modified black body function. We classify 48 sources as protostellar, based on their detection at 70 μm or at shorther wavelengths, and 218 as starless, because of non-detections at 70 μm. For two other sources, we do not provide a secure classification, but suggest they are Class 0 protostars.
Results. From the SED fitting we derived key physical parameters (i.e. mass, temperature, bolometric luminosity). Protostellar sources are in general warmer (⟨T⟩ = 12.8 K) and more compact (⟨diameter⟩ = 0.040 pc) than starless sources (⟨T⟩ = 10.3 K, ⟨ diameter ⟩ = 0.067 pc). Both these findings can be ascribed to the presence of an internal source(s) of moderate heating, which also causes a temperature gradient and hence a more peaked intensity distribution. Moreover, the reduced dimensions of protostellar sources may indicate that they will not fragment further. A virial analysis of the starless sources gives an upper limit of 90% probability for the sources to be gravitationally bound and therefore prestellar in nature. A luminosity vs. mass diagram of the two populations shows that protostellar sources are in the early accretion phase, while prestellar sources populate a region of the diagram where mass accretion has not started yet. We fitted a power law N(log M) ∝ M − 1.1 ± 0.2 to the linear portion of the mass distribution of prestellar sources. This is in between that typical of CO clumps and those of cores in nearby star-forming regions. We interpret this as a result of the inhomogeneity of our sample, which is composed of comparable fractions of clumps and cores.
Key words: ISM: individual objects: Vela-C / ISM: clouds / stars: formation / submillimeter: ISM / circumstellar matter
© ESO, 2012