2012MNRAS.426..402F

We present a Herschel far-infrared study towards the rich massive star-forming complex G305, utilizing PACS 70, 160µm and SPIRE 250, 350, and 500µm 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, H₂ O 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 x 10⁴ young stellar objects (YSOs) present, corresponding to a star formation rate (SFR) of 0.01–0.02M_☉/yr. 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.

Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.