Massive halos are not exactly self-similar. Differences in formation history and dynamical state drive variance in intrinsic properties at fixed mass/epoch, and astrophysical processes cause mean scalings to depart from scale-free, gravitational expectations. The relatively mild nature of these effects motivates a `soft' self-similar model that features multivariate, log-normal scatter about power-law mean behaviors. I will review aspects of this model for X-ray, optical and mm signatures, including supporting evidence from observation and simulation as well as implications for survey selection. Cluster samples can deviate from this simple model due to effects of projection, mis-centering and non-cluster source contamination. Modeling such effects is only beginning, and will be critical for accurate cosmological studies from next generate surveys.
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