Fragmentation of star-forming clouds enriched with the first dust

The thermal and fragmentation properties of star forming clouds have important consequences on the corresponding characteristic stellar mass. The initial composition of the gas within these clouds is a record of the nucleosynthetic products of previous stellar generations. In this paper, we present a model for the evolution of star forming clouds enriched by metals and dust from the first supernovae (SNe), resulting from the explosions of metal-free progenitors with masses in the range 12-30M(circle dot) and 140-260M(circle dot). Using a self-consistent approach, we show that: (i) metals depleted on to dust grains play a fundamental role, enabling fragmentation to solar or subsolar mass scales already at metallicities Z(cr) = 10(-6) Z(circle dot); (ii) even at metallicities as high as 10(-2) Z(circle dot), metals diffused in the gas phase lead to fragment mass scales which are greater than or similar to 100M(circle dot); (iii) C atoms are strongly depleted on to amorphous carbon grains and CO molecules so that CII plays a minor role in gas cooling, leaving OI as the main gas-phase cooling agent in low-metallicity clouds. These conclusions hold independently of the assumed SN progenitors and suggest that the onset of low-mass star formation is conditioned to the presence of dust in the parent clouds.