Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004bdmh.confe..94h&link_type=abstract
"Proceedings of "Baryons in Dark Matter Halos". Novigrad, Croatia, 5-9 Oct 2004. Editors: R. Dettmar, U. Klein, P. Salucci. Publ
Mathematics
Logic
Scientific paper
The diffuse cosmic UV-background caused by Quasars and massive stars photo-heats the gas in dark matter halos. It can be boiled out when the potential well of the halo is sufficiently shallow. Consequently, a lower mass limit for galaxy formation is set by the UV-background. Standard CDM structure formation models predict a significantly higher number of satellite dwarf galaxies in the Local Group than actually found. We study a similar substructure problem: pure N -body simulations predict a large number of dwarf galaxies in cosmological void regions but only few of them are found. For both the substructure problem of the Local Group and the missing dwarf galaxies in voids photo-heating is a promising mechanism in order to remove the discrepancies. In void regions at z = 0 we find that baryons are photo-evaporated in halos with mass below Mc ˜ 6 × 109 h-1 M . We argue the characteristic mass Mc at a given redshift is set by the ability of a halo to shock-heat infalling gas sufficiently to reach the instable branch of cooling/heating equilibrium at high densities in the gas phase-space diagram. The temperature in the cooling/heating equilibrium varies only slightly but the temperature in accretion shocks is essentially given by the virial temperature of a halo which evolves roughly ∝ (1 + z) for a given mass. Therefore, the characteristic mass scale Mc is much lower at earlier times. As a consequence those halos which are below Mc at present may have an early epoch of star formation. When the characteristic mass rises above the halo mass no new gas can be added to the star forming gas reservoir, but star formation out of the reservoir is still possible.
Gottlöber Stefan
Hoeft Matthias
Springel Volker
Yepes Gustavo
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