Jeong Gyu Kim, Woong Tae Kim, Eve Charis Ostriker

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64 Scopus citations


Dynamical expansion of H ii regions around star clusters plays a key role in dispersing the surrounding dense gas and therefore in limiting the efficiency of star formation in molecular clouds. We use a semianalytic method and numerical simulations to explore expansion of spherical dusty H ii regions and surrounding neutral shells and the resulting cloud disruption. Our model for shell expansion adopts the static solutions of Draine for dusty H ii regions and considers the contact outward forces on the shell due to radiation and thermal pressures, as well as the inward gravity from the central star and the shell itself. We show that the internal structure we adopt and the shell evolution from the semianalytic approach are in good agreement with the results of numerical simulations. Strong radiation pressure in the interior controls the shell expansion indirectly by enhancing the density and pressure at the ionization front. We calculate the minimum star formation efficiency required for cloud disruption as a function of the cloud's total mass and mean surface density. Within the adopted spherical geometry, we find that typical giant molecular clouds in normal disk galaxies have , with comparable gas and radiation pressure effects on shell expansion. Massive cluster-forming clumps require a significantly higher efficiency of for disruption, produced mainly by radiation-driven expansion. The disruption time is typically of the order of a free-fall timescale, suggesting that the cloud disruption occurs rapidly once a sufficiently luminous H ii region is formed. We also discuss limitations of the spherical idealization.

Original languageEnglish (US)
Article number137
JournalAstrophysical Journal
Issue number2
StatePublished - Mar 10 2016

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • H II regions
  • ISM: clouds
  • ISM: kinematics and dynamics
  • galaxies: star clusters: general
  • galaxies: star formation
  • stars: formation


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