The G305 star-forming complex: embedded massive star formation discovered by Herschel Hi-GAL

Faimali, A.; Thompson, M. A.; Hindson, L.; Urquhart, J. S.; Pestalozzi, M.; Carey, S.; Shenoy, S.; Veneziani, M.; Molinari, S. and Clark, J. S. (2012). The G305 star-forming complex: embedded massive star formation discovered by Herschel Hi-GAL. Monthly Notices of the Royal Astronomical Society, 426(1) p. 402.

DOI: https://doi.org/10.1111/j.1365-2966.2012.21765.x

Abstract

We present a Herschel far-infrared study towards the rich massive star- forming complex G305, utilising 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, 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 multi-wavelength dataset, that 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 star formation rate, to extragalactic star formation rate tracers (based on the Kennicutt-Schmidt relation), we find the star formation activity is underestimated by a factor of ≥ 2 in comparison to the SFR derived from the YSO population.

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