New catalogs of radio compact H II regions in the Milky Way

Details New catalogs of radio compact H II regions in the Milky Way New catalogs of radio compact H II regions in the Milky Way

Jun 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006phdt.........5g&link_type=abstract

PhD Thesis, Proquest Dissertations And Theses 2006. Section 0029, Part 0606 154 pages; [Ph.D. dissertation].United States -- Cal

Computer Science

H Ii Regions, Milky Way, Galactic Plane, Star Formation, Radio Flux Densities, B Stars

Scientific paper

This work presents a large sample of compact H II region candidates constructed by matching new VLA Galactic plane catalogs at 5 and 1.4 GHz covering the first and second Galactic quadrants (5 GHz: 350° <= l <= 42°, | b | <= 0.4° 1.4 GHz: 340° <= l <= 120°, | b | <= 0.8°) and the MSX6C Galactic plane catalog. Radio catalogs of this region were first published by Becker et al. (1994) and Zoonematkermani et al. (1990), but new observations were added and the data were re-reduced with significantly improved calibration and mosaicing procedures, resulting in a large increase of the number of detections. Comparison of these radio and infrared catalogs resulted in a sample of 687 MSX-5 GHz matches and 556 MSX-1.4 GHz matches. Most of the matches show red MSX colors and a thermal radio spectrum. The scale height of their Galactic latitude distribution is very small (FWHM of 16' or 40 pc for the 5 GHz sources for a distance of 8.5 kpc). The 1.4 GHz data indicate that their latitude distribution flattens out significantly above l [approximate] 40° and the number of matches drops off sharply. These properties suggest that the sample is dominated by young compact H II regions, most of which are previously uncataloged.
New sub-arcsecond resolution mid-infrared observations were obtained in a subsample of 18 sources with Keck/LWS. The goal of these observations was to determine the sizes, luminosities, and morphologies of regions of mid-infrared emitting dust surrounding the stellar sources. All 18 sources were imaged at 11.7 mm and at 17.65 mm, and 10 of them were imaged also at 24.5 mm. These images constitute a significant improvement in resolving sub-structure at these wavelengths in objects that were unresolved by MSX. Dust temperature and optical depth maps are presented and together with radial velocity measurements and radio data (1.4 and 5 GHz), they are used to constrain the properties of these star-forming regions. Half of our objects are excited by B-stars and not by O-stars. A significant correlation was found between infrared and radio flux densities, and a weaker one between infrared diameters and the central source ionizing photon rates. These data also suggest a revision to infrared color selection criteria of ultra-compact H II regions.

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