The impact of cosmic rays on population III star formation

We explore the implications of a possible cosmic racy (CR) background generated during the first supernova explosions that end the brief lives of massive Population III stars. We show that such a CR background could have significantly influenced the cooling and collapse of primordial gas clouds in minihalos around redshifts of z similar to 15-20, provided the CR, flux was sufficient to yield an ionization rate greater dian about 10(-19) s(-1) near the center of the minihalo. The presence of CRs with energies less than approximately 10(7) eV would indirectly enhance the molecular cooling in these regions, and we estimate that; the resulting lower temperatures in these minihalos would yield a characteristic stellar mass as low as similar to 10 M-circle dot. CRs have a less pronounced effect on the cooling and collapse of primordial gas clouds inside more massive dark matter halos with virial masses greater than approximately 10(8) M-circle dot at the later stages of cosmological structure formation around z similar to 10 - 15. In these clouds, even without the CR. flux, the molecular abundance is already sufficient, for cooling to the floor set by the temperature of the cosmic microwave background.