1996/03/31 by Max Tegmark, Joseph Silk, Martin Rees +3 · 1 citation
Physics and Astronomy · #astro-ph
paper · pdf · doi:10.1086/303434
published as Astrophys.J.474:1-12,1997 · Minor modifications to match published version. Molecular cooling rates improved. 29 pages, with 6 figures included. Color figures and related work at http://www.sns.ias.edu/~max/minmass.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/minmass.html (faster from Europe) or from [email protected]
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 profiles, 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 Mb is found to be strongly redshift dependent, dropping from 106 solar masses at z=15 to 5000 solar masses at z=100 as molecular cooling becomes effective. For z>>100, Mb rises again, as CMB photons inhibit H2-formation through the H- channel. Finally, for z>>200, the H2+ channel for H2-formation becomes effective, driving Mb down towards 103 solar masses. With a standard CDM power spectrum with sigma8=0.7, this implies that a fraction 10-3 of all baryons may have formed luminous objects by z=30, which could be sufficient to reheat the universe.