THE MOLECULAR PROPERTIES OF GALACTIC H II REGIONS
- Institute for Astrophysical Research, 725 Commonwealth Ave., Boston University, Boston MA 02215 (United States)
- Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
- Physikalisches Institut, Universitaet zu Koeln, 50937 Cologne (Germany)
- MIT Lincoln Laboratory, 244 Wood Street, Lexington, MA 02420 (United States)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138 (United States)
We derive the molecular properties for a sample of 301 Galactic H II regions including 123 ultra compact (UC), 105 compact, and 73 diffuse nebulae. We analyze all sources within the BU-FCRAO Galactic Ring Survey (GRS) of {sup 13}CO emission known to be H II regions based upon the presence of radio continuum and cm-wavelength radio recombination line emission. Unlike all previous large area coverage {sup 13}CO surveys, the GRS is fully sampled in angle and yet covers {approx}75 deg{sup 2} of the Inner Galaxy. The angular resolution of the GRS (46'') allows us to associate molecular gas with H II regions without ambiguity and to investigate the physical properties of this molecular gas. We find clear CO/H II morphological associations in position and velocity for {approx}80% of the nebular sample. Compact H II region molecular gas clouds are on average larger than UC clouds: 2.'2 compared to 1.'7. Compact and UC H II regions have very similar molecular properties, with {approx}5 K line intensities and {approx}4 km s{sup -1} line widths. The diffuse H II region molecular gas has lower line intensities, {approx}3 K, and smaller line widths, {approx}3.5 km s{sup -1}. These latter characteristics are similar to those found for quiescent molecular clouds in the GRS. Our sample nebulae thus show evidence for an evolutionary sequence wherein small, dense molecular gas clumps associated with UC H II regions grow into older compact nebulae and finally fragment and dissipate into large, diffuse nebulae.
- OSTI ID:
- 21269256
- Journal Information:
- Astrophysical Journal, Supplement Series, Vol. 181, Issue 1; Other Information: DOI: 10.1088/0067-0049/181/1/255; Country of input: International Atomic Energy Agency (IAEA); ISSN 0067-0049
- Country of Publication:
- United States
- Language:
- English
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