A Herschel study of YSO evolutionary stages and formation timelines in two fields of the Hi-GAL survey

D. Elia, E. Schisano, S. Molinari, T. Robitaille, D. Anglés-Alcázar, J. Bally, C. Battersby, M. Benedettini, N. Billot, L. Calzoletti, A. M. Di Giorgio, F. Faustini, J. Z. Li, P. Martin, L. Morgan, F. Motte, J.C. Mottram, P. Natoli, L. Olmi, R. PaladiniF. Piacentini, M. Pestalozzi, S. Pezzuto, D. Polychroni, M. Smith, F. Strafella, G. S. Stringfellow, L. Testi, M.A. Thompson, A. Traficante, M. Veneziani

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    We present a first study of the star-forming compact dust condensations revealed by Herschel in the two 2 \times 2 \degr Galactic Plane fields centered at [l;b] = [30\degr; 0 \degr] and [l;b] = [59\degr; 0 \degr], respectively, and observed during the Science Demonstration Phase for the Herschel infrared Galactic Plane survey (Hi-GAL) Key-Project. Compact source catalogs extracted for the two fields in the five Hi-GAL bands (70, 160, 250, 350 and 500 $\mu$m) were merged based on simple criteria of positional association and spectral energy distribution (SED) consistency into a final catalog which contains only coherent SEDs with counterparts in at least three adjacent Herschel bands. These final source lists contain 528 entries for the l = 30\degr field, and 444 entries for the l = 59\degr field. The SED coverage has been augmented with ancillary data at 24 $\mu$m and 1.1 mm. SED modeling for the subset of 318 and 101 sources (in the two fields, respectively) for which the distance is known was carried out using both a structured star/disk/envelope radiative transfer model and a simple isothermal grey-body. Global parameters like mass, luminosity, temperature and dust properties have been estimated. The Lbol/Menv ratio spans four orders of magnitudes from values compatible with the pre-protostellar phase to embedded massive zero-age main sequence stars. Sources in the l = 59\degr field have on average lower L/M, possibly outlining an overall earlier evolutionary stage with respect to the sources in the l = 30\degr field. Many of these cores are actively forming high-mass stars, although the estimated core surface densities appear to be an order of magnitude below the 1 g cm$^{-2}$ critical threshold for high-mass star formation.
    Original languageEnglish
    Article numberL97
    JournalAstronomy and Astrophysics
    Publication statusPublished - 11 May 2010


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