The SOFIA Mid-Infrared Giant H II Region Survey: Reassessing the Giant H II region Census of the Milky Way
Abstract
I will discuss the most recent results from our mid-infrared study of giant H II (GH II) regions in the Milky Way with the Stratospheric Observatory For Infrared Astronomy (SOFIA) aimed at understanding the evolution and physical properties of the most extreme sites of massive star formation in our Galaxy. GH II regions are defined as possessing a Lyman continuum photon rate, NLyC, of greater than 1050 photons/s, and the derivation of this value scales with source distance. Our survey utilizes a census of 56 Milky Way GH II regions identified by Conti & Crowther (2004), and our most recent paper discusses two sources from that list, Sgr D and W42. However, improved distance measurements have revealed much closer distances to both regions than previously believed, and consequently we claim that neither source is powerful enough to be considered GH II region any longer. Motivated by this, we performed a thorough literature search to update each source from the GH II census with the most recent and/or most accurate distance measurements. In particular, we found that many regions have new and very accurate distances derived via parallactic measurements from radio masers or GAIA, or via spectrophotometric means. Based on these new distance estimates, we determine 25% of the sources have sufficiently reliable and closer distances and are not powerful enough to be considered GH II regions. Of the remaining 42 GH II region candidates, an additional 20% have measurement errors that could place them below the NLyC cut-off criterion for being considered bona fide GH II regions.
- Publication:
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American Astronomical Society Meeting Abstracts
- Pub Date:
- January 2023
- Bibcode:
- 2023AAS...24123503D