The effect of photoionization on the cooling rates of enriched, astrophysical plasmas

By R. Wiersma, Joop Schaye, Britton D. Smith. 2008

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A B ST R A C T Radiativecooling iscentralto a widerangeofastrophysicalproblem s.Despiteits im portance,cooling ratesaregenerally com puted using very restrictiveassum ptions, such as collisionalionization equilibrium and solar relative abundances.W e sim ul- taneously relax both assum ptions and investigate the eects ofphoto-ionization of heavy elem entsby them eta-galacticUV/X-ray background and ofvariationsin rela- tiveabundanceson thecoolingratesofopticallythin gasin ionization equilibrium .W e �nd thatphoto-ionization by them eta-galacticbackground radiation reducesthenet cooling ratesby up to an orderofm agnitudeforgasdensitiesand tem peraturestyp- icalofthe shock-heated intergalactic m edium and proto-galaxies(10 4 K< T < 10 6 K, �=hi < 100).In addition,photo-ionization changesthe relative contributionsofdif- ferentelem entstothecoolingrates.W econcludethatphoto-ionization by theionizing background and heavy elem entsboth need to be taken into accountin orderforthe cooling ratesto be correctto orderofm agnitude.M oreover,ifthe ratesneed to be known to better than a factor ofa few,then departures ofthe relative abundances from solar need to be taken into account.W e propose a m ethod to com pute cool- ing rateson an elem ent-by-elem entbasisby interpolating pre-com puted tables that take photo-ionization into account.W e provide such tables for a popular m odelof the evolving UV/X-ray background radiation,com puted using the photo-ionization package cloudy. K ey w ords: atom icprocesses| plasm as| coolingows| galaxies:form ation | intergalacticm edium

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Citations in the corpus

On the evolution of the H i column density distribution in cosmological simulations (2012, methodology): “Chemical evolution is followed using the model of Wiersma et al. (2009b), which traces the abundance evolution of eleven elements by following stellar evolution assuming a Chabrier (2003) initial mass function.”
The effects of galaxy formation on the matter power spectrum: a challenge for precision cosmology (2011, background): “This implementation of stellar evolution and chemical enrichment is discussed in Wiersma et al. (2009).”
The origin of discs and spheroids in simulated galaxies (2011, methodology): “Chemical enrichment is modelled as described by Wiersma et al. (2009b), and tracks the synthesis of 11 individual elements.”
The transition from population III to population II-I star formation (2010, background): “…evolve and die according to their characteristic l fetimes, possibly expelling newly created metals into the surrounding gas and modifying its cooling properties either at low (e.g. Maio et al. 2007) and at high temperatures (e.g. Sutherland & Dopita 1993; Wiersma et al. 2009; Cantalupo 2010).”
The rates and modes of gas accretion on to galaxies and their gaseous haloes (2010, background): “This minimum coincides with a maximum at T ≈ 105–105.5 K in the cooling function (e.g. Wiersma et al. 2009a).”
Physical Processes in the Interstellar Medium (2014, background): “10, taken from the study of Wilson et al. (2005). Their observations reveal a complex hierarchy of filaments and clumps on all resolved scales.”
Feedback and recycled wind accretion: assembling the z= 0 galaxy mass function (2009, methodology): “Hydrodynamic simulations that explicitly incorporate winds into them are more successful than those without winds at reproducing other aspects of galaxy evolution and IGM enrichment.”
ON LYMAN-LIMIT SYSTEMS AND THE EVOLUTION OF THE INTERGALACTIC IONIZING BACKGROUND (2011, background): “This metallicity is insufficient for metals to be the dominant coolant at T & 20, 000 K, which requires Z & 10−1 Z⊙ (Wiersma et al. 2009).”