Astrophys. J., 709, 191-209 (2010/January-3)
The disruption of giant molecular clouds by radiation pressure and the efficiency of star formation in galaxies.
MURRAY N., QUATAERT E. and THOMPSON T.A.
Abstract (from CDS):
Star formation is slow in the sense that the gas consumption time is much longer than the dynamical time. It is also inefficient; star formation in local galaxies takes place in giant molecular clouds (GMCs), but the fraction of a GMC converted to stars is very small, εGMC∼ 5%. In luminous starbursts, the GMC lifetime is shorter than the main-sequence lifetime of even the most massive stars, so that supernovae can play no role in GMC disruption. We investigate the disruption of GMCs across a wide range of galaxies from normal spirals to the densest starbursts; we take into account the effects of H II gas pressure, shocked stellar winds, protostellar jets, and radiation pressure produced by the absorption and scattering of starlight on dust grains. In the Milky Way, a combination of three mechanisms–jets, H II gas pressure, and radiation pressure–disrupts the clouds. In more rapidly star-forming galaxies such as "clump" galaxies at high-redshift, ultra-luminous infrared galaxies (ULIRGs), and submillimeter galaxies, radiation pressure dominates natal cloud disruption. We predict the presence of ∼10-20 clusters with masses ∼107 M☉ in local ULIRGs such as Arp 220 and a similar number of clusters with M*∼ 108 M☉ in high redshift clump galaxies; submillimeter galaxies will have even more massive clusters. We find that εGMC = πGΣGMCc/(2(L/M*)) for GMCs that are optically thin to far-infrared radiation, where ΣGMC is the GMC gas surface density. The efficiency in optically thick systems continues to increase with ΣGMC, but more slowly, reaching ∼35% in the most luminous starbursts. The disruption of bubbles by radiation pressure stirs the interstellar medium (ISM) to velocities of ∼10 km/s in normal galaxies and to ∼100 km/s in ULIRGs like Arp 220, consistent with observations. Thus, radiation pressure may play a dominant dynamical role in the ISM of star-forming galaxies.
galaxies: formation - galaxies: general - galaxies: starburst - galaxies: star clusters: general - H II regions - ISM: bubbles - ISM: clouds - stars: formation
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