A millimeter survey of ultra-compact HII-regions and associated molecular clouds

Type Journal Article
Names E. Churchwell, A. Sievers, C. Thum
Publication Astronomy and Astrophysics
Volume 513
Pages 9
Date April 1, 2010
URL http://adsabs.harvard.edu/abs/2010A%26A...513A...9C
Library Catalog NASA ADS
Abstract We report observations, using the IRAM 30 m telescope, of 30 ultracompact and hypercompact HII regions in the lines of HCO+(3-2) and/or HCO+(1-0) and H30α and/or H39α. Images are presented in both HCO+(3-2) and H30α toward a subset of regions (16 in HCO+(3-2), 14 in H30α) with a resolution of 12”. In addition, H13CO+(3-2) observations are reported toward 13 HII regions where HCO+(3-2) displays complex profiles. It is shown that the absorption dips in the HCO+ profiles are due to HCO+ self-absorption, not absorption of the HII free-free emission or warm dust emission surrounding the HII region or two velocity components along the line of sight. It was found that among the sources with self-absorbed profiles, 8 are contracting and 5 are expanding. Mass fluxes are found to be typically a few times 10-3 M_ȯ yr-1, implying time scales for massive star formation <105 yrs. HCO+ and H2 column densities are estimated for a subset of the sources from which masses of the dense central cloud cores were estimated. Implications of the derived column densities, masses, flow velocities, and mass fluxes are discussed. Maps are available in electronic form from the authors (e-mail: sievers@iram.es).
Tags HII regions, STARS: FORMATION, surveys
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