Effects of Preheating on X‐Ray Scaling Relations in Galaxy Clusters

The failure of purely gravitational models of X-ray cluster formation toreproduce basic observed properties of the local cluster population suggeststhe need for one or more additional physical processes operating on theintracluster medium (ICM). We present results from 84 moderate resolution gasdynamic simulations designed to systematically investigate the effects ofpreheating - an initially elevated ICM adiabat - on the resultant, local X-raysize-temperature, luminosity-temperature and ICM mass-temperature relations.Seven sets of twelve simulations are performed for a LambdaCDM cosmology, eachset characterized by a different initial entropy level S_i. The slopes of theobservable relations steepen monotonically as S_i is increased. Observed slopesfor all three relations are reproduced by models with S_i: 55-150 keV cm^2,levels that compare favorably to empirical determinations of core ICM entropyby Lloyd-Davies, Ponman & Cannon. The redshift evolution for the case of alocally successful model with S_i = 106 keV cm^2 is presented. At temperatureskT > 3 keV, little or no evolution in physical isophotal sizes or bolometricluminosities is expected to z < 1. The ICM mass at fixed T is lower at higher zas expected in the canonical evolution model. ICM mass fractions show a mild Tdependence. Clusters with T > 3 keV contain ICM mass fractions depressed bymodest amounts (< 25%) below the cosmic mean baryon fraction Omega_b/Omega_m;hot clusters subject to preheating remain good tracers of the cosmic mix ofclustered mass components.Comment: 15 pages, 13 figures, submitted to ApJ, revised size-temperature analysis, changes in response to referee repor