Resolution of the Distance Ambiguity for Inner Galaxy HII Regions

Details Resolution of the Distance Ambiguity for Inner Galaxy HII Regions Resolution of the Distance Ambiguity for Inner Galaxy HII Regions

May 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.1802a&link_type=abstract

American Astronomical Society, AAS Meeting #212, #18.02; Bulletin of the American Astronomical Society, Vol. 40, p.212

Astronomy and Astrophysics

Astronomy

Scientific paper

Most of the current sites of massive star formation are in the Inner Galaxy. We are engaged in a multi-wavelength study of the physical properties of Galactic HII regions. Our nebular sample contains all HII regions with measured radio recombination line emission that lie in the first quadrant zone where the SPITZER GLIMPSE and BU-FCRAO 13-CO Galactic Ring Survey (GRS) overlap. This sample of 289 nebulae contains ultra compact, compact, and diffuse HII regions. Here we establish kinematic distances to 260 HII regions using the 21cm HI VLA Galactic Plane Survey and the 13-CO GRS. We use two methods for resolving the distance ambiguity for each HII region: HI self-absorption (HISA) and HI emission/absorption (HIE/A). The HISA method is able to resolve the distance ambiguity for 󕿀% of our sample, while the HIE/A method is able to resolve the distance ambiguity for 󕾶% of our sample. We estimate that the HISA method is accurate 󕿅% of the time, while the HIE/A method is accurate 󕿏% of the time. When projected onto the Galactic plane, this large sample appears to reveal aspects of Galactic structure, with spiral arm-like features at 4.5 and 6 kpc, and a lack of HII regions within 3.5 kpc of the Galactic Center. Our HII regions are located approximately in the ratio of 2 to 1 for far verses near distances, as one would expect from geometrical effects.

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