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Unformatted text preview: the mixing happened early on, since type IIs would have gone off before type Ia's). There is some evidence that significant heating can occur from supernova-driven winds, on top of the virial heating simply from being in equilibrium in the cluster potential. It was believed for some time, from the Einstein serendipity survey, that the X-ray luminosity function of clusters showed string evolution from about z =0.5 to the present in the direction of clusters brightening over time, but more complete ROSAT data call this into question and suggest that cluster X-ray properties have been nearly constant since z =0.7 (the WARPS survey - Fairley et al. 2000 MNRAS 315, 669; and Schindler 1999 A&A 349, 435). Out to redshifts of order 1, X-ray emission is the best way to identify rich groupings of galaxies, since detection of diffuse emission is less subject to projection biases than enhancements in projected galaxy density....
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