Astronomy and Astrophysics – Astrophysics
Scientific paper
Jun 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009a%26a...500.1119n&link_type=abstract
Astronomy and Astrophysics, Volume 500, Issue 3, 2009, pp.1119-1129
Astronomy and Astrophysics
Astrophysics
4
Ism: Clouds, Ism: H Ii Regions, Stars: Evolution, Stars: Formation, Radio Lines: Ism
Scientific paper
Aims: We examined the physical properties of molecular clouds (morphology, column density, number density, mass) to investigate the mechanism of triggered star formation by UV radiation from a massive star. Methods: We made extensive, high-resolution maps of molecular clouds associated and interacting with the W5-East H ii region using the 45-m telescope at the Nobeyama Radio Observatory (HPBW = 15.6 arcsec) in 13CO (J = 1-0) and C18O (J = 1-0) to reveal details in the high-density regions of the molecular clouds. In addition, to investigate the spatial distributions of young stellar objects (YSOs) in the W5-East H ii region, we mapped the spatial distributions of Class I and II candidates. Results: We identified eight 13CO molecular clouds (three of them are known bright-rimmed clouds) and nine 18O clumps. The masses of the clouds and clumps range from 460 to 36 000 M&sun; and from 55 to 740 M&sun;, respectively. The peak 13CO column densities of the clouds facing the H ii region are twice as large as the others. They have steep density gradients toward the H ii region, indicating interactions with the H ii region. We selected 55 Class I candidates and 778 Class II candidates associated with the W5-East H ii region from the previous Spitzer IRAC/MIPS survey. Most Class I candidates are located around integrated intensity peaks of 13CO, whereas most Class II candidates are distributed along the front sides of the BRC arcs close to the exciting star. Conclusions: The alignments of the YSO candidates and the molecular clouds in order of age indicate that triggered star formation occurs in the W5-East H ii region as a result of gas compression by strong UV radiation. Based on the column densities of 13CO and the spatial distribution of YSO candidates, we identified a new bright-rimmed cloud candidate on the west side of the W5-East H ii region.
Itoh Yusuke
Mukai Tadashi
Niwa Takahiro
Oasa Yumiko
Sugitani Kenichiro
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