DID COSMIC-RAYS REIONIZE THE INTERGALACTIC MEDIUM

We investigate the role of cosmic rays from young galaxies in heating and ionizing the intergalactic medium (IGM) at high redshift. Using th e IRAS observations at 60 mum, we estimate the cosmic ray luminosity d ensity at the present epoch. We consider various forms of luminosity e volution in redshift, and calculate (i) the thresholds corresponding t o the upper limits of Gunn-Peterson optical depth, (ii) the Compton y- parameter for an IGM heated by cosmic rays (and compare it with the up per limits from COBE measurements), and (iii) an estimated limit from the integral of metal enrichment. We show that certain models, with ra ther strong evolution and early formation of galaxies, allow reionizat ion of the IGM, consistent with all known constraints.