The metal enrichment and temperature of the intergalactic medium

Hydrodynamic simulations of Ly alpha clouds based on ab initio cosmological models have produced results that are in broad agreement with observations . However, further analyses have revealed that, with progressively higher n umerical resolution, the median or cutoff line width of the simulated Ly al pha clouds (i.e., the Doppler parameter) appears to converge to a value sig nificantly below what is observed at z similar to3 (by about a factor of 1. 5). These simulations do not include feedback from star formation. We sugge st that, given the observed metallicity in the Ly alpha clouds, it is possi ble that supernovae, which presumably polluted the intergalactic medium (IG M) with metals, may have deposited a sufficient amount of energy in the IGM to reconcile the theory with observations. Simple arguments immediately na rrow the redshift range of pollution down to 4 < z(dep) <9. It seems quite certain that dwarf and subdwarf galaxies with masses in the range of 10(6.5 )-10(9.0) M-. have to be largely responsible for the pollution. Furthermore , it is implied that either star formation is very efficient or the metal y ield is very high for these early dwarf galaxies, if the mean metallicity i n the universe at z=3 is as high as [Z] = 10(-2) Z(.).