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

作者：Churchwell E^*; Sievers A; Thum C

来源：Astronomy & Astrophysics, 2010, 513: A9.

DOI：10.1051/0004-6361/200912241

• surveys
• stars: formation
• HII regions

We report observations, using the IRAM30 m telescope, of 30 ultracompact and hypercompact HII regions in the lines of HCO(+)(3-2) and/or HCO(+)(1-0) and H30 alpha and/or H39 alpha. Images are presented in both HCO(+)(3-2) and H30 alpha toward a subset of regions (16 in HCO(+)(3-2), 14 in H30 alpha) with a resolution of 12 ''. In addition, H(13)CO(+)(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(circle dot) yr(-1), implying time scales for massive star formation <10(5) yrs. HCO(+) and H(2) 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.

• 出版日期2010-4