The G305 star-forming complex: embedded massive star formation discovered byHerschelHi-GAL

Abstract

We present a Herschel far-infrared study towards the rich massive star-forming complex G305, utilizing PACS 70, 160 μm and SPIRE 250, 350, and 500 μm observations from the Hi-GAL survey of the Galactic plane. The focus of this study is to identify the embedded massive star-forming population within G305, by combining far-infrared data with radio continuum, H2O maser, methanol maser, MIPS and Red MSX Source survey data available from previous studies. By applying a frequentist technique we are able to identify a sample of the most likely associations within our multiwavelength data set, which can then be identified from the derived properties obtained from fitted spectral energy distributions (SEDs). By SED modelling using both a simple modified blackbody and fitting to a comprehensive grid of model SEDs, some 16 candidate associations are identified as embedded massive star-forming regions. We derive a two-selection colour criterion from this sample of log (F70/F500) ≥ 1 and log (F160/F350) ≥ 1.6 to identify an additional 31 embedded massive star candidates with no associated star formation tracers. Using this result we can build a picture of the present-day star formation of the complex, and by extrapolating an initial mass function, suggest a current population of ≈2 × 104 young stellar objects (YSOs) present, corresponding to a star formation rate (SFR) of 0.01–0.02 M⊙ yr−1. Comparing this resolved SFR, to extragalactic SFR tracers (based on the Kennicutt–Schmidt relation), we find that the star formation activity is underestimated by a factor of ≥2 in comparison to the SFR derived from the YSO population.