STELLAR FEEDBACK IN MOLECULAR CLOUDS AND ITS INFLUENCE ON THE MASS FUNCTION OF YOUNG STAR CLUSTERS

Abstract

We investigate how the removal of interstellar material by stellar feedback\nlimits the efficiency of star formation in molecular clouds and how this\ndetermines the shape of the mass function of young star clusters. In\nparticular, we derive relations between the power-law exponents of the mass\nfunctions of the clouds and clusters in the limiting regimes in which the\nfeedback is energy-driven and momentum-driven, corresponding to minimum and\nmaximum radiative losses and likely to bracket all realistic cases. We find\ngood agreement between the predicted and observed exponents, especially for\nmomentum-driven feedback, provided the protoclusters have roughly constant mean\nsurface density, as indicated by observations of the star-forming clumps within\nmolecular clouds. We also consider a variety of specific feedback mechanisms,\nconcluding that HII regions inflated by radiation pressure predominate in\nmassive protoclusters, a momentum-limited process when photons can escape after\nonly a few interactions with dust grains. We then present a first estimate of\nthe star formation efficiency in this case, finding that it depends on the\nmasses and sizes of the protoclusters only through their mean surface density,\nthus ensuring consistency between the observed power-law exponents of the mass\nfunctions of the clouds and clusters. The numerical value of this efficiency is\nalso consistent with observations.\n