Cosmic rays and the primordial gas |
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| Authors: | Jens Jasche Benedetta Ciardi Torsten A Enßlin |
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| Institution: | Max-Planck-Institut für Astrophysik, Karl-Schwarzschild Strasse 1, D-85748 Garching, Germany |
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| 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 ≤ 104 K , molecular hydrogen is needed for further cooling down to temperatures T ～ 100 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 (CRs). In order to investigate this possibility, we developed a code to study the effects of ionizing CRs on the thermal and chemical evolution of primordial gas. We found that CRs 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 erg cm?2 Hz?1 s?1 , initial temperature of the gas ～103 K , total gas number densities n ≥ 1 cm?3 , and cosmic-ray sources with  . |
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| Keywords: | astrochemistry cosmic rays |
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