The evolutionary stages of high-mass young stellar objects in close-by massive star-forming regions
HOBYS consortium coordinated by F. Motte, A. Zavagno, S. Bontemps
The HOBYS Herschel survey targets the close-by massive star-forming regions to provide an unbiased census of high-mass (HM) young stellar objects (YSOs). Already the first results brought up candidates for intermediate-mass (IM) to HM analogues of the prestellar/Class 0 phase. We present identified populations of cores in the more recently surveyed regions (Cygnus X, W48, NGC6334/NGC6357) and their bolometric luminosities, sizes, and masses. Using a Mass versus Luminosity diagram, we intercompare the findings towards the regions and use evolutionary tracks to examine the present stages. HOBYS delivers statistically significant samples of YSOs down to low masses and a number of massive cores. The early Class 0 phase in the IM to HM regime is accessed and a subset of the sources are newly identified with Herschel. Intriguingly, candidate HM YSOs are found both towards prominent massive aggregates (e.g. DR21) and more isolated. HM star formation has progressed to a different degree, and may be phasing out in some of the regions.