The Dependence of Fragmentation of Metal-Deficient Gas Clouds on H2and HD Cooling and the Initial Mass Function of First Generation Stars

Abstract

Recent threee-dimensional numerical simulations have shown that a filamentary structure is one of the most prominent features in the structure formation of the early universe. Fragmentation of the filamentary clouds is expected to lead to the formation of first generation stars. In this context, we have studied the gravitational collapse and fragmentation of filamentary clouds with axisymmetric hydrodynamic simulations coupled with non-equilibrium chemistry of H 2 and HD. In this paper we review our recent results and show some supplemental numerical result Special attention is paid to the dynamical stability of the filamentary clouds and the role of HD cooling which becomes more dominant than H 2 cooling in some intergalactic environments. Our simulations suggest that the first generation stars are deficient in sub-solar mass stars. According to these simulations, a typical mass of low-mass first stars should be of order of 1M O .,and a typical mass of massive first stars should be around 10 2 M O .or 10M O ..depending on the H 2 fractional abundance, which determines the efficiency of HD cooling. We predict that the stellar IMF is bimodal with two peaks at 1- 2M O .and 10M O .or 10M O ..