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Title:
Modeling primordial gas in numerical cosmology
Authors:
Abel, Tom; Anninos, Peter; Zhang, Yu; Norman, Michael L.
Affiliation:
AA(Laboratory for Computational Astrophysics, National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 405 N. Mathews Ave., Urbana, IL 61801, USA), AB(Laboratory for Computational Astrophysics, National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 405 N. Mathews Ave., Urbana, IL 61801, USA), AC(Laboratory for Computational Astrophysics, National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 405 N. Mathews Ave., Urbana, IL 61801, USA), AD(Laboratory for Computational Astrophysics, National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 405 N. Mathews Ave., Urbana, IL 61801, USA)
Publication:
New Astronomy, vol. 2, no. 3, p. 181-207. (NewA Homepage)
Publication Date:
08/1997
Origin:
NEWA
Keywords:
ATOMIC PROCESSES, MOLECULAR PROCESSES, PLASMAS, ISM: MOLECULES, RADIATION MECHANISMS: THERMAL
DOI:
10.1016/S1384-1076(97)00010-9
Bibliographic Code:
1997NewA....2..181A

Abstract

We have reviewed the chemistry and cooling behavior of low-density (n <~ 10^4 cm^-3) primordial gas and devised a model which involves 19 collisional and 9 radiative processes and is applicable for temperatures in the range 1 K < T < 10^8 K. In a companion paper (Anninos et al., 1997)[NewA, 2, 209] numerical methods are presented that unify the modeling of non-equilibrium primordial gas chemistry and cooling dicussed here with cosmological hydrodynamics. We derived new fits of rate coefficients for the photo-attachment of neutral hydrogen, the formation of molecular hydrogen via H^-, charge exchange between H_2 and H^+, electron detachment of H^- by neutral hydrogen, dissociative recombination of H_2^+ with slow electrons, photodissociation of H_2^+, and photodissociation of H_2. Furthermore it was found that the molecular hydrogen produced through the gas-phase processes, H_2^+ + H --> H_2 + H^+, and H^- + H --> H_2 + e^-, is likely to be converted into its para configuration on a faster time scale than the formation time. We have tested the model extensively and shown it to agree well with former studies. We further studied the chemical kinetics in great detail and devised a minimal model which is substantially simpler than the full reaction network but predicts correct abundances. This minimal model shows convincingly that 12 collisional processes are sufficient to model the H, He, H^+, H^-, He^+, He^++, and H_2 abundances in low density primordial gas for applications with no radiation fields.
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