2006MNRAS.369.1437S

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_☉and 140-260M_☉. 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^–6Z_☉; (ii) even at metallicities as high as 10^–2Z_☉, metals diffused in the gas phase lead to fragment mass scales which are ≳100M_☉; (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.