The disruption of giant molecular clouds by radiation pressure & the efficiency of star formation in galaxies

Norman Murray, Eliot Quataert, Todd A. Thompson

Research output: Contribution to journalArticle

287 Scopus citations

Abstract

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 = πGΣGMC c/(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-1 in normal galaxies and to ∼ 100 km s -1 in ULIRGs like Arp 220, consistent with observations. Thus, radiation pressure may play a dominant dynamical role in the ISM of star-forming galaxies.

Original languageEnglish (US)
Pages (from-to)191-209
Number of pages19
JournalAstrophysical Journal
Volume709
Issue number1
DOIs
StatePublished - 2010
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Keywords

  • Galaxies: formation
  • Galaxies: general
  • Galaxies: star clusters: general
  • Galaxies: starburst
  • Hii regions
  • ISM: bubbles
  • ISM: clouds
  • Stars: formation

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