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18th of December 2018
A census of southern HII regions
by Wenger et al.
Massive OB-type stars ionize the gas surrounding them, creating H II regions. Since these nebulae have short lifetimes (~10 Myr) they are the locations of current high-mass star formation in the Galaxy. A complete census of Galactic H II regions would inform models of both Galactic kinematics as well as the formation and chemo-dynamical evolution of the Galaxy. However, the census of Galactic H II regions is vastly incomplete in the Southern sky. Wenger et al. have used the Australia Telescope Compact Array (ATCA) to observe 4–10 GHz radio continuum and hydrogen radio recombination line (RRL) emission from southern candidate H II regions within 4 degrees of the galactic plane. Their first data release targetted 282 candidate fields and detected radio continuum emission and RRL emission in 275 (97.5%) and 258 (91.5%) of these fields, respectively. The discovery of RRL emission from these nebulae increases the number of known Galactic H II regions in the surveyed zone by 82%, to 568 nebulae. Details are given in the preprint of the paper which will be published in the Astrophysical Journal Supplement Series.

The image above shows an infrared image of a typical H II region candidate from the WISE Catalog, G309.176−00.028. The image is a composite of WISE 22µm (red), 12µm (green), and 3.4µm (blue) data. The black contours are the SHRDS 7 GHz continuum emission (50 mJy/beam to 250 mJy/beam in 50 mJy/beam intervals). The hatched ellipse represents the ATCA half-power synthesized beam.

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