A Universal Temperature Profile for Galaxy Clusters

We investigate the predicted present-day temperature profiles of the hot, X-ray-emitting gas in galaxy clusters for two cosmological models—a current best-guess ΛCDM model and a standard cold dark matter (SCDM) model. Our numerically simulated catalogs of clusters are derived from high-resolution (15 h-1 kpc) simulations which make use of a sophisticated, Eulerian-based, adaptive mesh-refinement code that faithfully captures the shocks that are essential for correctly modeling cluster temperatures. We show that the temperature structure on Mpc scales is highly complex and non-isothermal. However, the temperature profiles of the simulated ΛCDM and SCDM clusters are remarkably similar and drop off as T ∝ (1 + r/ax)-δ, where ax ~ rvir/1.5 and δ ~ 1.6. This decrease is in good agreement with the observational results of Markevitch et al. but diverges, primarily in the innermost regions, from their fit which assumes a polytropic equation of state. Our result is also in good agreement with a recent sample of clusters observed by BeppoSAX, though there is some indication of missing physics at small radii (r 0.2 rvir, our universal temperature profile is consistent with our most recent simulations, which include both radiative cooling and supernovae feedback.