Feedback Regulated Star Formation: From Star Clusters to Galaxies
  This paper summarises results from semi-analytical modelling of star
formation in protocluster clumps of different metallicities. In this model,
gravitationally bound cores form uniformly in the clump following a prescribed
core formation efficiency per unit time. After a contraction timescale which is
equal to a few times their free-fall times, the cores collapse into stars and
populate the IMF. Feedback from the newly formed OB stars is taken into account
in the form of stellar winds. When the ratio of the effective wind energy of
the winds to the gravitational energy of the system reaches unity, gas is
removed from the clump and core and star formation are quenched. The power of
the radiation driven winds has a strong dependence on metallicity and increases
with increasing metallicity. Thus, winds from stars in the high metallicity
models lead to a rapid evacuation of the gas from the protocluster clump and to
a reduced star formation efficiency, SFE_{exp}, as compared to their low
metallicity counterparts. By combining SFE_{exp} with the timescales on which
gas expulsion occurs, we derive the metallicity dependent star formation rate
per unit time in this model as a function of the gas surface density Sigma_{g}.
This is combined with the molecular gas fraction in order to derive the
dependence of the surface density of star formation Sigma_{SFR} on Sigma_{g}.
This feedback regulated model of star formation reproduces very well the
observed star formation laws extending from low gas surface densities up to the
starburst regime. Furthermore, the results show a dependence of Sigma_{SFR} on
metallicity over the entire range of gas surface densities, and can also
explain part of the scatter in the observations.
