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 currentbest-guess LCDM model and standard cold dark matter (SCDM). Ournumerically-simulated "catalogs" of clusters are derived from high-resolution(15/h kpc) simulations which make use of a sophisticated, Eulerian-based,Adaptive Mesh-Refinement (AMR) code that faithfully captures the shocks whichare essential for correctly modelling cluster temperatures. We show that thetemperature structure on Mpc-scales is highly complex and non-isothermal.However, the temperature profiles of the simulated LCDM and SCDM clusters areremarkably similar and drop-off as $T +AFw-propto (1+-r/a_x)^{-+AFw-delta}$where $a_x +AFw-sim r_{vir}/1.5$ and $+AFw-delta +AFw-sim 1.6$. This decreaseis in good agreement with the observational results of Markevitch et al.(1998)but diverges, primarily in the innermost regions, from their fit which assumesa polytropic equation of state. Our result is also in good agreement with arecent sample of clusters observed by BeppoSAX though there is some indicationof missing physics at small radii ($r<0.2 r_{vir}$). We discuss theinterpretation of our results and make predictions for new x-ray observationsthat will extend to larger radii than previously possible. Finally, we showthat, for $r>0.2 r_{vir}$, our universal temperature profile is consistent withour most recent simulations which include both radiative cooling and supernovaefeedback.