Simulating galaxy clusters¿ III. Properties of the intracluster stars

Cosmological (� -cold dark matter) TREESPH simulations of the formation and evolution of galaxy groups and clusters have been performed. The simulations invoke star formation, chemical evolution with non-instantaneous recycling, metallicity-dependent radiative cooling, strong starburst, and (optionally) active galactic nuclei, driven galactic superwinds, effects of a metagalactic ultraviolet field and thermal conduction. Results for two clusters, one Virgo-like (T � 3k eV) and one (sub-) Coma-like (T � 6k eV), are presented. At z = 0 the stellar con- tents of both clusters consist of a central dominant (cD) galaxy surrounded by cluster galaxies and intracluster (IC) stars. The IC stars are found to contribute 20-40 per cent of the total cluster B-band luminosity at z = 0 and to form at a mean redshiftf ∼ 3, which is on average approximately 0.5 Gyr older than the stars in cluster galaxies. UBVRIJHK surface brightness profiles of the IC star populations are presented; the profile of the larger cluster matches the observed V-band profile of the cD in Abell 1413 (T � 8k eV) quite well. The typical colour of the IC stellar population is B − R = 1.4-1.5, comparable to the colour of sub-L ∗ E and S0 galaxies. The mean iron abundance of the IC stars is approximately solar in the central part of the cluster (r ∼ 100 kpc) decreasing to approximately half solar at the virial radius. The IC stars are α-element enhanced with a weak trend of (O/Fe) increasing with r and an overall (O/Fe) ∼ 0.4 dex, indicative of dominant enrichment from Type II supernovae. The IC stars are kinematically significantly colder than the cluster galaxies: the velocity dispersions of the IC stars are in the inner parts of the clusters (r ∼ 100-500 kpc) only approximately half of those of the cluster galaxies, increasing slightly outward to approximately 70 per cent at r = 1-2 Mpc. The typical projected velocity dispersion in the Virgo-like cluster at R 50 kpc is 300-600 km s −1 , depending on orientation and projected distance from the cluster centre. Rotation is found to be dynamically insignificant for the IC stars. The velocity distributions of IC stars and clusters galaxies are highly radially anisotropic in one cluster and in the other close to being isotropic. Ke yw ords: galaxies: clusters: general - galaxies: evolution - galaxies: formation - cosmology: theory.

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