EDP Sciences
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Volume 398, Number 3, February II 2003
Page(s) L35 - L39
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361:20021877

A&A 398, L35-L39 (2003)
DOI: 10.1051/0004-6361:20021877


Reproducing the entropy structure in galaxy groups

A. Finoguenov1, S. Borgani2, 3, L. Tornatore2 and H. Böhringer1

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

(Received 24 October 2002 / Accepted 19 December 2002 )

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 $M_{500}=1.0{-}16\times10^{13}~h^{-1}\,M_{\odot}$ 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  $z_{\rm h}=3$, 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, $z_{\rm h}=9$, strongly delays the star-formation, but fails to produce a sufficiently high specific entropy.

Key words: clusters: cosmology -- cosmic star-formation

Offprint request: A. Finoguenov, alexis@xray.mpe.mpg.de

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