Formation and Disruption of Cosmological Low-Mass Objects

We investigate the evolution of cosmological low-mass (low virial temperature) objects and the formation of the first luminous objects. First, the "cooling diagram" for low-mass objects is shown. We assess the cooling rate taking into account the contribution of H 2 , which is not in chemical equilibrium generally, with a simple argument of timescales. The reaction rates and the cooling rate of H 2 are taken from the recent results by Galli & Palla. Using this cooling diagram, we also estimate the formation condition of luminous objects taking into account the supernova (SN) disruption of virialized clouds. We find that the mass of the first luminous object is several times 10 7 M ☉ because smaller objects may be disrupted by the SNe before they become luminous. Metal pollution of low-mass (Lyα) clouds is also discussed. The resultant metallicity of the clouds is Z / Z ☉ ~ 10 -3 .