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Star Formation Thresholds

Published online by Cambridge University Press:  01 June 2007

Joop Schaye*
Affiliation:
Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, the Netherlands email: schaye@strw.leidenuniv.nl
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Abstract

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To make predictions for the existence of “dark galaxies”, it is necessary to understand what determines whether a gas cloud will form stars. Star formation thresholds are generally explained in terms of the Toomre criterion for gravitational instability. I contrast this theory with the thermo-gravitational instability hypothesis of Schaye (2004), in which star formation is triggered by the formation of a cold gas phase and which predicts a nearly constant surface density threshold. I argue that although the Toomre analysis is useful for the global stability of disc galaxies, it relies on assumptions that break down in the outer regions, where star formation thresholds are observed. The thermo-gravitational instability hypothesis can account for a number of observed phenomena, some of which were thought to be unrelated to star formation thresholds.

Type
Contributed Papers
Copyright
Copyright © International Astronomical Union 2008

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