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). We discuss the interpretation of our results and make predictions for new X-ray observations that will extend to larger radii than previously possible. Finally, we show that for r > 0.2 rvir, our universal temperature profile is consistent with our most recent simulations, which include both radiative cooling and supernovae feedback.