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The Genesis of Super Star Clusters as Self-Gravitating HII Regions
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The Genesis of Super Star Clusters
as Self-Gravitating HII Regions
Jonathan C. Tan1 and Christopher F. McKee2
1 Dept. of Astronomy, UC Berkeley, Berkeley, CA 94720, USA
2 Depts. of Physics and of Astronomy, UC Berkeley, Berkeley, CA 94720, USA
Abstract. We examine the effects of ionization, radiation pressure and main sequence
winds from massive stars on self-gravitating, clumpy molecular clouds, thereby mod-
eling the formation and pre-supernova feedback of massive star clusters. We find the
process of “turbulent mass loading” is effective in confining HII regions. Extrapolating
typical Galactic high-mass star forming regions to greater initial gas cloud masses and
assuming steady star formation rates, we determine the timescales for cloud disruption.
We find that a dense (nc ? 2 × 10
5 cm?3) cloud with initial mass Mc ? 4 × 10
5 M⊙
is able to form ～ 2 × 105 M⊙ of stars (50% efficiency) before feedback disperses the
gas after ～ 3 Myr. This mass and age are typical of young, optically visible super star
clusters (SSCs). The high efficiency permits the creation of a bound stellar system.
1 Introduction
Most Galactic stars are born in highly clustered regions [12,5], where the disrup-
tive effects of massive stars are paramount. The multitude of dusty high redshift
sources and the intensity of the far infrared background they produce also imply
that a major fraction (～ 1/2) of total cosmic star formation has occurred in star-
bursts, replete with massive stars [20]. A significant fraction of star formation in
local starbursts occurs via the creation of super star clusters (SSCs) [22,24], each
with hundreds to thousands of OB stars crammed into a few parsecs. At least
some SSCs are gravitationally bound [8,9] and their masses (～ 105 ? 106 M⊙
[19,15]) and sizes suggest we may have found globular clusters in their infancy.
Massive stars violently disrupt their surroundings with ionizing and non-
ionizin
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