Impact of Cosmic Rays on Population III Star Formation

TL;DR

This paper investigates how cosmic rays from early supernovae could have affected the cooling, collapse, and resulting stellar masses of primordial gas clouds during the formation of Population III stars in the early universe.

Contribution

It introduces the potential impact of cosmic ray backgrounds on primordial star formation, highlighting their role in lowering stellar masses in minihaloes at high redshifts.

Findings

CRs could significantly influence gas cooling in minihaloes at z ~ 15-20.

Lower stellar masses (~10 M_sun) may result from CR-enhanced cooling.

CR effects are less significant in larger haloes at z ~ 10-15.

Abstract

We explore the implications of a possible cosmic ray (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 minihaloes around redshifts of z ~ 15 - 20, provided the CR flux was sufficient to yield an ionization rate greater than 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 minihaloes would yield a characteristic stellar mass as low as ~ 10 M_sun. CRs have a less pronounced effect on the cooling and collapse of primordial gas clouds inside more massive dark matter haloes with virial masses greater than approximately 10^8 M_sun at the later stages of cosmological structure formation around z ~ 10 - 15. In these clouds, even without CR flux the molecular abundance is already sufficient to allow cooling to the floor set by the temperature of the cosmic microwave background.