A New Radio Catalog of Compact HII Regions in the Milky Way II. The 1.4 GHz Data

Abstract

We utilize a new VLA Galactic plane catalog at 1.4 GHz covering the first and second Galactic quadrants (340 deg <l< 120 deg, |b|<0.8 deg with |b|< 1.8 deg for 350 deg <l< 40 deg and |b|<2.5 deg for 100 deg <l<105 deg) in conjunction with the MSX6C Galactic plane mid-infrared catalog to supplement and better understand our 5 GHz catalog (Giveon et al. 2005). A radio catalog of this region was first published by Zoonematkermani et al. (1990), but we have re-reduced the data with significantly improved calibration and mosaicing procedures, resulting in more than a tripling of the number of 1.4 GHz sources detected. Comparison of the new 1.4 GHz catalog and the MSX6C catalog resulted in a sample of 556 matches, out of which we estimate only 11 to be chance coincidences. Most of the matches show red MSX colors. The scale height of their Galactic latitude distribution is 24'-28' (FWHM) or ~60-70 pc (for a distance of 8.5 kpc), depending on longitude. The latitude distribution flattens out significantly above l~40 deg and the number of matches drops off sharply.