Radio observations of massive star-forming regions

Details Radio observations of massive star-forming regions Radio observations of massive star-forming regions

Jan 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993phdt........40k&link_type=abstract

PhD Dissertation, Wisconsin Univ. Madison, WI United States

Astronomy and Astrophysics

Astronomy

2

H Ii Regions, Radio Astronomy, Star Formation, Stellar Spectra, Infrared Astronomy Satellite, Photoionization, Flux Density, Star Clusters, Dust, Stellar Luminosity

Scientific paper

Radio continuum observations were made of 59 IRAS sources with far-infrared colors suggesting ultracompact (UC) H II regions. 75 sources were detected at 3.6 and 2 cm; we provide contour plots and flux density distributions ranging from the radio to the near-infrared. Over half are unresolved and their morphologies undetermined. The remaining sources can be described by five morphological classes whose frequency of occurrence is consistent with the Wood and Churchwell survey. We calculate physical properties of the nebulae and show that they are consistent with UC photoionized regions. Alternative explanations are explored and found to be unlikely. The correlation of UC H II positions with proposed spiral arms is examined and reasonable agreement found only for the local arm. No enhancement of UC H II regions is apparent along the proposed Sagittarius and Scutum arms, probably due to inaccuracies in the kinematic distances. We find the latitude distribution of UC H II regions to lie in the range 0.5 deg less than or = (b FWHM) less than or = 0.8 deg. No size-density correlation of cometary and core-halo UC H II regions is found, consistent with the bow of shock interpretation of these morphologies. Spherical and unresolved UC H II regions, however, show a trend toward lower densities with increasing size, as expected for expanding H II regions. Observed ratios of far-infrared to radio flux densities of UC H II regions lie in the range 103 to approximately greater than 105. We show that this ratio depends on spectral type, ranging from approximately 103 for an O4 star to greater than 105 for a B3 star. Over half of the UC H II regions in our sample must be excited by a cluster of stars, and virtually all contain significant amounts of dust. Spectral line observations were made of 384 IRAS sources that have far-infrared colors suggesting UC H II regions. 64 percent have localized CO emission near the IRAS position. Distances and luminosities are reported for many of the 274 sources with local CO emission and we investigate possible correlations of CO line parameters, distance, luminosity, and IRAS flux densities. We examine the spatial distribution of the sources; no evidence for galactic structure is seen. Some clustering is seen in longitude-velocity space. We investigate the relative velocity of the CO lines with ammonia and radio recombination lines. Fifty-four outflow candidates are identified, based on the appearance of their spectra.

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