Research Note

Probing the astrophysics of cluster outskirts

¹ Dip. Fisica, Univ. “Tor Vergata”, via Ricerca Scientifica 1, 00133 Roma, Italy e-mail: lapi@roma2.infn.it
² SISSA, via Bonomea 265, 34136 Trieste, Italy
³ INAF-IASF, via Fosso del Cavaliere, 00133 Roma, Italy

Received: 8 February 2010
Accepted: 17 April 2010

Abstract

In galaxy clusters the entropy distribution of the intracluster plasma (ICP) modulates the latter's equilibrium within the dark matter gravitational wells, as rendered by our supermodel. We argue the entropy production at the boundary shocks to be reduced or terminated as the accretion rates of DM and intergalactic gas peter out; this behavior is enforced by the slowdown in the outskirt development at late times, when the dark energy dominates the cosmology while the outer wings of the initial perturbation drive the growth. For these conditions, we predict the ICP temperature profiles to steepen into the cluster outskirts. The detailed expectations from our simple formalism agree with the X-ray data concerning five clusters whose temperature profiles have been recently measured out to the virial radius. We predict steep temperature declines to prevail in clusters at low z, tempered only by rich environs including adjacent filamentary structures.