The Gunn Peterson effect: a test for a black holes induced photoionization of the intergalactic medium

Abstract

Many experimental evidences indicate the presence of a ionizing background radiation flux at large redshifts; in some previous works I suggested the possibility that this ionizing flux comes from the quantum evaporation of primordial black holes (PBHs). Here I discuss the constraints that the experimental measurements put upon the free parameters of this reionization model and I study the absorption of the ionizing background due to $\lia$ clouds: in particular, I discuss this phenomenon in presence of different absorption levels and I calculate the HI Gunn Peterson optical depth ${\tau }_{GP}(z)$; from a comparison with the experimental data I obtain a constraint on the intergalactic medium density parameter, namely ${\Omega }_{IGM}$ $<0.020$. A study of the characteristics of the absorbers is also performed; finally, the same kind of analysis is repeated for He II.

Plain Tex, 36 pages. Accepted for Pub. in Int. Jour. of Mod. Phys. A

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