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U. Giveon, M.J. Richter (UC Davis), R.H. Becker (UC Davis and LLNL), R.L. White (STScI)
We present data from mid-infrared Keck imaging of 18 radio-selected ultra-compact HII regions candidates at diffraction-limited resolution. The goal of these observations is to determine the sizes, luminosities, and morphologies of the mid-IR emission regions of dust that is directly heated by the stellar sources. All 18 sources were imaged at 11.7um and at 17.65um, and 10 of them were imaged also at 24.5um. Six of these sources are previously unidentified. We have generated dust temperature and optical depth maps and combine them with radial velocity measurements and radio data (1.4 and 5 GHz) to constrain the properties of these star-forming regions. We find significant correlations between infrared and radio flux densities, and between infrared diameters and the central source ionizing photon rates. Our new data also suggest a revision to selection criteria of ultra-compact HII regions. These 18 sources are part of a sample of 687 ultra-compact HII regions selected by matching radio and infrared maps of the first Galactic quadrant by Giveon and coworkers. The new images constitute a significant improvement in resolving sub-structure at these wavelengths. When applied to all of this sample our analysis will improve our understanding of embedded star formation in the Galaxy.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.