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28 January 2022
  » arxiv » 1302.0159

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Non-equilibrium cooling rate for a collisionally cooled metal-enriched gas
Evgenii O. Vasiliev ;
Date 1 Feb 2013
AbstractWe present self-consistent calculations of non-equilibrium (time-dependent) cooling rates for a dust-free collisionally controlled gas in wide temperature ($10 Kle Tle 10^8 K$) and metallicity ($10^{-4} Z_odot le Z le 2 Z_odot$) ranges. We confirm that molecular hydrogen dominates cooling at $10^2 simlt Tsimlt 10^4$ K and $Zsimlt 10^{-3} Z_odot$. We find that the contribution from H$_2$ into cooling rate around $Tsim (4-5) imes 10^3$ K stimulates thermal instability in the metallicity range $Zsimlt 10^{-2} Z_odot$. Isobaric cooling rates are generally lower than isochoric ones, because the associated increase of gas density leads to both more efficient hydrogen recombination and equilibration of the fine-structure level populations. Isochoric cooling keeps the ionization fraction remains quite high at $Tsimlt10^4$ K: up to $sim0.01$ at $Tsimeq 10^3$ K and $Zsimlt 0.1 Z_odot$, and even higher at higher metallicity, contrary to isobaric cooling where it at least an order of magnitude lower. Despite this increase in ionization fraction the gas-phase formation rate of molecular hydrogen (via H$^-$) lowers with metallicity, because higher metallicity shorttens the evolution time. We implement our self-consistent cooling rates into the multi-dimensional parallel code ZEUS-MP in order to simulate evolution of a supernova remnant, and compare it with an analogous model with tabulated cooling rates published in previous works. We find significant differences between the two descriptions, which may appear, e.g., in mixing of the ejected metals in the circumstellar medium.
Source arXiv, 1302.0159
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