The Green Bank Telescope Galactic H II Region Discovery Survey

Details The Green Bank Telescope Galactic H II Region Discovery Survey The Green Bank Telescope Galactic H II Region Discovery Survey

May 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21630902b&link_type=abstract

American Astronomical Society, AAS Meeting #216, #309.02; Bulletin of the American Astronomical Society, Vol. 41, p.871

Astronomy and Astrophysics

Astronomy

Scientific paper

We discovered a large population of previously unknown Galactic HII regions by using the NRAO Green Bank Telescope to detect hydrogen radio recombination line (RRL) emission from these nebulae. Since recombination lines are optically thin at 3 cm wavelength, we can detect HII regions across the entire Galactic disk. Our targets were selected based on spatially coincident 24µm (Spitzer/MIPSGAL) and 21 cm (either from the VLA Galactic Plane Survey or the NRAO NVSS) continuum emission. For the Galactic zone, -16° < Lgal < 67° and |Bgal|<1°, we detected 602 discrete RRL components from 95% of the sample targets, which more than doubles the number of known HII regions in this part of the Milky Way. We found 25 new first quadrant nebulae with negative RRL velocities, placing them beyond the Solar orbit in the Perseus arm. We plan to determine the distance to over 90% of our sources (for the region Lgal>18°) by using HI emission/absorption experiments to resolve the kinematic distance ambiguity. Because we can detect all nebulae inside the Solar orbit that are ionized by O-stars, the Discovery Survey targets, when combined with existing HII region catalogs, will give a more accurate census of Galactic HII regions and their properties. The distribution of HII regions across the Galactic disk shows strong, narrow ( 1 kpc wide) peaks at Galactic radii of 4.3 and 6.0 kpc. There is still an overall dearth of HII regions within 4 kpc radius. For the first time the longitude-velocity distribution of HII regions gives unambiguous evidence for Galactic structure, including the kinematic signatures of the radial peaks in the spatial distribution, a concentration of nebulae at the end of the Galactic Bar, and nebulae located in kinematic locus of the 3 kpc Arm.

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