2010A&A...520A..50S

Although current facilities allow the study of Galactic star formation at high angular resolution, our current understanding of the high-mass star-formation process is still very poor. In particular, we still need to characterize the properties of clouds giving birth to high-mass stars in our own Galaxy and use them as templates for our understanding of extragalactic star formation. We present single-dish (sub)millimeter observations of gas and dust in the Galactic high-mass star-forming region G19.61-0.23, with the aim of studying the large-scale properties and physical conditions of the molecular gas across the region. The final aim is to compare the large-scale (about 100pc) properties with the small-scale (about 3pc) properties and to consider possible implications for extragalactic studies. We have mapped CO isotopologues in the J=1-0 transition using the FCRAO-14m telescope and the J=2-1 transition using the IRAM-30m telescope. We have also used APEX 870µm continuum data from the ATLASGAL survey and FCRAO supplementary observations of the ¹³CO J=1-0 line from the BU-FCRAO Galactic Ring Survey, as well as the Spitzer infrared Galactic plane surveys GLIMPSE and MIPSGAL to characterize the star-formation activity within the molecular clouds. We reveal a population of molecular clumps in the ¹³CO(1-0) emission, for which we derived the physical parameters, including sizes and masses. Our analysis of the ¹³CO suggests that the virial parameter (ratio of kinetic to gravitational energy) varies over an order of magnitude between clumps that are unbound and some that are apparently ``unstable''. This conclusion is independent of whether they show evidence of ongoing star formation. We find that the majority of ATLASGAL sources have MIPSGAL counterparts with luminosities in the range 10⁴-5x10⁴L_☉ and are presumably forming relatively massive stars. We compare our results with previous extragalactic studies of the nearby spiral galaxies M31 and M33; and the blue compact dwarf galaxy Henize 2-10. We find that the main giant molecular cloud surrounding G19.61-0.23 has physical properties typical for Galactic GMCs and which are comparable to the GMCs in M31 and M33. However, the GMC studied here shows smaller surface densities and masses than the clouds identified in Henize 2-10 and associated with super star cluster formation.