DISRUPTION OF MOLECULAR CLOUDS BY EXPANSION OF DUSTY H II REGIONS

ABSTRACT 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...

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Bibliographic Details
Published in:The Astrophysical journal 2016-03, Vol.819 (2), p.137
Main Authors: Kim, Jeong-Gyu, Kim, Woong-Tae, Ostriker, Eve C.
Format: Article
Language:English
Subjects:
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Clouds
COMPARATIVE EVALUATIONS
Computer simulation
COMPUTERIZED SIMULATION
Constraining
COSMIC DUST
COSMIC GASES
DENSITY
Disruption
EFFICIENCY
Evolution
EXPANSION
GALAXIES
galaxies: star clusters: general
galaxies: star formation
GRAVITATION
H II regions
H2 REGIONS
IONIZATION
ISM: clouds
ISM: kinematics and dynamics
MASS
Mathematical models
Molecular clouds
RADIATION PRESSURE
regions
STAR CLUSTERS
STAR EVOLUTION
STARS
stars: formation
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Summary:ABSTRACT 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.
ISSN:0004-637X
1538-4357
DOI:10.3847/0004-637X/819/2/137