A millimeter survey of ultra-compact HII-regions and associated molecular clouds*
Department of Astronomy, University of Wisconsin-Madison, 475 N. Charter street, Madison, WI 53706, USA e-mail: firstname.lastname@example.org
2 Instituto de Radio Astronomía Milimétrica, Avenida Divina Pastora, 7 Núcleo Central, 18012 Granada, Spain e-mail: email@example.com
3 Institut de Radio Astronomie Millimétrique, Domaine Universitaire de Grenoble, 300 rue de la Piscine, 38406 Saint Martin d'Hères, France
Accepted: 18 November 2009
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 H and/or H. Images are presented in both HCO+(3-2) and H toward a subset of regions (16 in HCO+(3-2), 14 in H) 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 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.
Key words: surveys / stars: formation / HII regions
© ESO, 2010