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J.J. Mohr (U Illinois, Urbana-Champaign), M.B. Hoffman (U Chicago), J.J. Bialek, A.E. Evrard (U Michigan)
Large cluster surveys which extend to intermediate and high redshift are powerful cosmological probes. Survey yields per solid angle depend on (i) the volume per solid angle as a function of redshift, (ii) the evolution of cluster number density with redshift, and (iii) the virial mass of the minimally detectable cluster as a function of redshift. The first two of these dependences are well understood theoretically for a wide range of cosmological parameters; however, the third dependence is more problematic, because it requires an understanding of the evolution of the relationship between the cluster virial mass and cluster observables like the X-ray emission weighted temperature, X-ray luminosity and Sunyaev-Zel'dovich effect (SZE) decrement.
We use hydrodynamical simulations of cluster formation to examine the effects of preheating-- the entropy increase in intergalactic gas before cluster formation-- on X-ray and SZE cluster survey yields. The source of this preheating is presumably galaxy formation, and evidence supporting preheating (or perhaps some other physics) lies in the steepness of the local X-ray luminosity-temperature, intracluster medium mass-temperature and X-ray isophotal size-temperature relations. We tune the preheating level to reproduce these local cluster scaling relations.
We use these simulations to estimate the impact of preheating on the accuracy of cosmological parameters inferred from X-ray and SZE cluster surveys. Finally, we discuss future observations which can further constrain preheating models, and we discuss analyses which are less sensitive to biases from unknown aspects of preheating.
JJM is supported by Chandra Fellowship grant PF8-1003, awarded through the Chandra Science Center. AEE acknowledges support from NSF AST-9803199 and NASA NAG5-8458.
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