Journal
ASTROPHYSICAL JOURNAL
Volume 566, Issue 1, Pages 302-314Publisher
IOP PUBLISHING LTD
DOI: 10.1086/338030
Keywords
HII regions; ISM : clouds; stars : formation
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We argue that massive stars are the dominant sources of energy for the turbulent motions within giant molecular clouds and that the primary agent of feedback is the expansion of H II regions within the cloud volume. This conclusion is suggested by the low efficiency of star formation and corroborated by dynamical models of H II regions. We evaluate the turbulent energy input rate in clouds more massive than 3.7 x 10(5) M., for which gravity does not significantly affect the expansion of H II regions. Such clouds achieve a balance between the decay of turbulent energy and its regeneration in H II regions; summed over clouds, the implied ionizing luminosity and star formation rate are roughly consistent with the Galactic total. H II regions also photoevaporate their clouds : we derive cloud destruction times somewhat shorter than those estimated by Williams & McKee. The upper mass limit for molecular clouds in the Milky Way may derive from the fact that larger clouds would destroy themselves in less than 1 crossing time. The conditions within starburst galaxies do not permit giant molecular clouds to be supported or destroyed by H II regions, and this may explain some aspects of the starburst phenomenon.
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