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U. Giveon, R.H. Becker (UC Davis), D.J. Helfand (Columbia University), R.L. White (STScI)
Investigation of the color-space properties of mid-infrared sources in the MSX Galactic plane catalog reveals two distinct populations - a blue population composed mainly of evolved stars, masers and molecular clouds, and a red population comprising sources of a nebular nature - HII regions, planetary nebulae, and unclassified radio sources. We compare the MSX catalog to 5 GHz VLA maps of the first quadrant of the Galactic plane. A catalog extracted from these maps was published first by Becker et al., but we have re-reduced the data with significantly improved calibration and mosaicing procedures, resulting in an increase of ~ 60% in the number of detected sources. Comparison of the radio and infrared catalogs resulted in a sample of 491 matches, out of which we estimate 38 to be false counterparts, all of them from the MSX red population. The radio sources with infrared counterparts are found to have extremely small scale height (FWHM of 14' or ~35 pc), and have thermal radio spectrum. These properties suggest that the sample is dominated by HII regions, most of them are previously uncataloged. This research is supported be the National Science Foundation.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.