Molecular clouds and star formation in the southern H II regions: Dynamical effects of H II regions on star formation

Abstract

Extensive (13)CO (J = 1 - 0) observations have been performed toward 23 H II regions associated with bright-rimmed clouds and identified 95 molecular clouds. Active formation of massive stars is found on the side adjacent to the H II regions, which is a consequence of dynamical effects of H II regions, such as accumulation and compression of molecular gas. To test the effects of H II regions, the clouds were divided into two parts, i.e., the side faced to H II regions (near side) and that separated from H II regions (far side). The clouds on the near side are effectively forming massive stars with approximately greater than 10(exp 3) solar luminosity. Luminosity to mass ratios, L(sub IRAS)/M(sub clouds), are higher by an order of magnitude on the near side than those on the far side. The number density of the IRAS (Infrared Astronomical Satellite) sources also increases by a factor of two on the near side compared with that on the far side. The present Star Formation Rate (SFR) due to the effects of H II regions is estimated to be at least approximately 0.1 - 0.4 solar mass yr(exp -1), which corresponds to approximately 10 - 30 percent of the Galactic SFR.

散光星雲を伴う23のHII領域を(13)CO(J=1-0)分子線で広範に観測し、95の分子雲を同定した。HII領域のすぐ外側で活発な大質量星の形成が見られた。これは、分子ガスの蓄積と圧縮などの、HII領域の力学的影響の結果である。HII領域の影響を調べるため、分子雲を2つの部分に分けた。すなわち、HII領域に接している側(近い側)と、HII領域から離れた側(遠い側)である。近い側の分子雲では、10(exp 3)太陽光度以上の大質量星が効率的に生まれていた。光度質量比L(sub IRAS)/M(sub cloud)は、遠い側に比べて、近い側の方が1桁大きかった。IRAS(赤外線天文学衛星)天体の数密度も、外側に比べて内側では2倍大きくなっていた。また、HII領域の影響による現在の星生成率(SFR)は、少なくとも年間0.1?0.4太陽質量であると見積もった。これは、銀河系の星生成率の10?30%に相当する。