Cosmic rays and the primordial gas

Abstract

One of the most outstanding problems in the gravitational collapse scenario of early structure formation is the cooling of primordial gas to allow for small mass objects to form. As the neutral primordial gas is a poor radiator at temperatures (T\le10^4\unit{K}), molecular hydrogen is needed for further cooling down to temperatures (T\sim100\unit{K}). The formation of molecular hydrogen is catalyzed by the presence of free electrons, which could be provided by the ionization due to an early population of cosmic rays. In order to investigate this possibility we developed a code to study the effects of ionizing cosmic rays on the thermal and chemical evolution of primordial gas. We found that cosmic rays can provide enough free electrons needed for the formation of molecular hydrogen, and therefore can increase the cooling ability of such primordial gas under following conditions: A dissociating photon flux with (F<10^{-18}\unit{erg cm^{-2} Hz^{-1} s^{-1}}), initial temperature of the gas (\sim10^{3}\unit{K}), total gas number densities (n\ge1\unit{cm^{-3}}), Cosmic ray sources with (\dotε_{CR}>10^{-33}\unit{erg cm^{-3} s^{-1}}).

15 pages, 5 figures

References in corpus (3)

• Detecting shock waves in cosmological smoothed particle hydrodynamics simulations
• The impact of dark matter decays and annihilations on the formation of the first structures
• Cosmological production of H_2 before the formation of the first galaxies

Cited by in corpus (5)

• Uncertainties in H2 and HD Chemistry and Cooling and their Role in Early Structure Formation
• Occurrence of Metal-free Galaxies in the Early Universe
• Is H3+ cooling ever important in primordial gas?
• Conditions for HD Cooling in the First Galaxies Revisited: Interplay between Far-Ultraviolet and Cosmic Ray Feedback in Population III Star Formation
• Open questions in the study of population III star formation