Letter to the Editor

Reproducing the entropy structure in galaxy groups

¹ Max-Planck Institut für extraterrestrische Physik, Giessenbachstraße 1, 85748 Garching, Germany
² Dipartimento di Astronomia, Università di Trieste, via Tiepolo 11, 34131 Trieste, Italy
³ INAF, Istituto Nazionale di Astrofisica; INFN, Sezione di Trieste, Trieste, Italy

Corresponding author: A. Finoguenov, alexis@xray.mpe.mpg.de

Received: 24 October 2002
Accepted: 19 December 2002

Abstract

We carry out a comparison between observations and hydrodynamic simulations of entropy profiles of groups and clusters of galaxies. We use the Tree+SPH GADGET code to simulate four halos of sizes in the  range, corresponding to poor groups up to Virgo-like clusters. We concentrate on the effect of introducing radiative cooling, star formation, and a variety of non-gravitational heating schemes on the entropy structure and the stellar fraction. We show that all the simulations result in a correct entropy profile for the Virgo-like cluster. With the heating energy budget of ~0.7 keV/particle injected at , we are also able to reproduce the entropy profiles of groups. We obtain the flat entropy cores as a combined effect of preheating and cooling, while we achieve the high entropy at outskirts by preheating. The resulting baryon fraction locked into stars is in the 25–30% range, compared to 35–40% in the case of no preheating. Heating at higher redshift, , strongly delays the star-formation, but fails to produce a sufficiently high specific entropy.