Molecular clouds and star formation in the inner galaxy - A comparison of CO, H II, and far-infrared surveys

Abstract

The authors have compared surveys of the galactic plane over -1° ≤ b ≤ 1°, 12° ≤ l ≤ 60°, in the CO line at 2.6 mm, in the far-infrared (FIR) continuum at 150 μm and 250 μm, and in the radio continuum and H 110α recombination line at 6 cm. They identify 54 molecular cloud complexes, with mean mass ≡10<SUP>6</SUP>M_sun;. Most FIR sources are coincident with H II regions, and nearly all H II regions in turn are associated with molecular clouds. The stellar content of a cloud is estimated by assuming that the associated FIR and radio continuum emission result from clusters whose mass distribution is the same as the initial mass function. The star formation efficiency (SFE) for the entire sample lies near 0.02, but some massive clouds are extremely star-poor, with SFE less than 10<SUP>-3</SUP>. The stellar mass in a cloud appears correlated with the cloud mass, as M<SUB>*</SUB> ∝ M<SUB>cloud</SUB><SUP>0.5±0.2</SUP>.