as tr o - ph / 9 60 30 07 4 M ar 1 99 6 HOW SMALL WERE THE FIRST COSMOLOGICALOBJECTS ? 1
نویسندگان
چکیده
The minimum mass that a virialized gas cloud must have in order to be able to cool in a Hubble time is computed, using a detailed treatment of the chemistry of molecular hydrogen. With a simple model for halo prooles, we reduce the problem to that of numerically integrating a system of chemical equations. The results agree well with numerically expensive 3D simulations, and our approach has the advantage of rapidly being able to explore large regions of parameter space. The minimum baryonic mass M b is found to be strongly redshift dependent, dropping from 10 6 M at z 15 to 510 3 M at z 100 as molecular cooling becomes eeective. For z 100, M b rises again, as CMB photons inhibit H 2-formation through the H channel. Finally, for z 200, the H + 2-channel for H 2-formation becomes eeective, driving M b down towards M b 10 3 M. With a standard CDM power spectrum with 8 = 0:7, this implies that a fraction 10 3 of all baryons may have formed luminous objects by z = 30, which could be suucient to reheat the universe.
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