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Time-dependent Ionization in Radiatively Cooling Gas

Gnat, Orly and Sternberg, Amiel (2007) Time-dependent Ionization in Radiatively Cooling Gas. Astrophysical Journal Supplement Series, 168 (2). pp. 213-230. ISSN 0067-0049.

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We present new computations of the equilibrium and nonequilibrium cooling efficiencies and ionization states for low-density radiatively cooling gas containing the elements H, He, C, N, O, Ne, Mg, Si, S, and Fe. We present results for gas temperatures between 10^4 and 10^8 K, assuming dust-free and optically thin conditions, and no external radiation. For nonequilibrium cooling we solve the coupled time-dependent ionization and energy loss equations for a radiating gas cooling from an initially hot, ≳5 × 10^6 K, equilibrium state, down to 10^4 K. We present results for heavy element compositions ranging from 10^(-3) to 2 times the elemental abundances in the Sun. We consider gas cooling at constant density (isochoric) and at constant pressure (isobaric). We calculate the critical column densities and temperatures at which radiatively cooling clouds make the dynamical transition from isobaric to isochoric evolution. We construct ion ratio diagnostics for the temperature and metallicity in radiatively cooling gas. We provide numerical estimates for the maximal cloud column densities for which the gas remains optically thin to the cooling radiation. We present our computational results in convenient online figures and tables.

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Additional Information:© 2007 American Astronomical Society. Received 2006 June 13; accepted 2006 August 8. We thank Gary Ferland for his invaluable assistance in our nonstandard use of CLOUDY. We thank Hagai Netzer for generously providing us with his up-to-date ION atomic data set.We thank Chris McKee for many helpful discussions. Our research is supported by the US-Israel Binational Science Foundation (grant 2002317).
Funding AgencyGrant Number
US-Israel Binational Science Foundation2002317
Subject Keywords:atomic processes; intergalactic medium; ISM: general; plasmas; quasars: absorption lines
Issue or Number:2
Record Number:CaltechAUTHORS:20100423-135234589
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Official Citation:Orly Gnat and Amiel Sternberg 2007 ApJS 168 213 doi: 10.1086/509786
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18058
Deposited By: Jason Perez
Deposited On:27 Apr 2010 17:18
Last Modified:03 Oct 2019 01:37

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