Molecular Clouds and Star Formation in the Southern H II Regions

Details Molecular Clouds and Star Formation in the Southern H II Regions Molecular Clouds and Star Formation in the Southern H II Regions

Dec 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999pasj...51..791y&link_type=abstract

Publications of the Astronomical Society of Japan, v.51, p.791-818.

Astronomy and Astrophysics

Astronomy

44

Ism: H Ii Regions, Ism: Molecules, Radio Lines: Ism, Stars: Early-Type, Stars: Formation

Scientific paper

We have carried out extensive 13CO(J = 1-0) observations toward 23 southern H II regions associated with bright-rimmed clouds. In total, 95 molecular clouds have been identified to be associated with the H II regions. Among the 95, 57 clouds \ are found to be associated with 204 IRAS point sources which are candidates for young stellar objects. There is a significant increase of star-formation efficiency on the side facing to the H II regions; the luminosity-to-mass ratio, defined as the ratio of the stellar luminosity to the molecular cloud mass, is higher by an order of magnitude on the near side of the H II \ regions than that on the far side. This indicates that molecular gas facing to the H II regions is more actively forming massive s\ tars whose luminosity is >~ 103 LO . In addition, the number density of the IRAS point sources increases by a factor of 2 on the near side of the H II regions compared with on the far side. These results strongly suggest that the active formation of massive stars on the near side of the H II regions is due to the effects of the H II regions, such as the compression of molecular material by the ionization/shock fronts. For the whole Galaxy, we estimate that the present star-formation rate under such effects is at least 0.2-0.4 MO yr-1, corresponding to a few 10% by mass.

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