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Myers, P.C., T.M. Dame, P. Thaddeus, R.S. Cohen, R.F. Silverberg, E. Dwek, and M.G. Hauser, 1986: Molecular clouds and star formation in the inner galaxy - A comparison of CO, H II, and far-infrared surveys. Astrophys. J., 301, 398-422, doi:10.1086/163909.
We 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 110-alpha recombination line at 6 cm. We identify 54 molecular cloud complexes, with mean mass ~106 M☉. Most FIR sources are coincident with H II regions, and nearly all H II regions in turn are associated with molecular clouds. Clouds without H II regions tend to have lower mass than clouds with H II regions. The stellar content of a cloud is estimated by assuming that the associated FIR and radio continuum 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 10-3. The stellar mass in a cloud appears correlated with the cloud mass, as M* ∝ Mcloud0.5±0.2. The mean gas density in a typical large complex is ~20 cm-3 with volume filling fraction less than 0.1; the time to grow by accretion to this density is 107-108 yr. Presently visible inner Galaxy clouds have probably been forming stars of all types for less than 108 yr but may have been forming O stars for only the most recent ~20% of their lives.
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