Simulating Galaxy Clusters - III: Properties of the Intracluster Stars

Abstract

Cosmological (LCDM) TreeSPH simulations of galaxy clusters have been performed, invoking star-formation, chemical evolution with non-instantaneous recycling, metal dependent radiative cooling, strong star-burst and/or AGN driven super-winds, effects of a meta-galactic UV field and thermal conduction. Results for two clusters, one Virgo-like (T~3 keV) and one (sub) Coma-like (T~6 keV), are presented. At z=0, the stellar contents of both clusters consist of a central dominant (cD) galaxy surrounded by galaxies and intracluster (IC) stars. The IC stars are found to contribute 20-40% of the total cluster B-band light and to form at a mean redshift z_f~3, on average about 0.5 Gyr prior to the stars in 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~8 keV). The IC stellar populations have B-R=1.4-1.5, comparable to larger E galaxies. The mean [Fe/H]~0.0 in the central part of the cluster (r~100 kpc) decreasing to about -0.3 at r_vir. The IC stars are alpha-element enhanced, with a weak trend of [O/Fe] increasing with r, and an overall [O/Fe]~0.4 dex. The IC stars are kinematically colder than the galaxies: The velocity dispersions of the IC stars are at r~100-500 kpc only about half of those of the galaxies increasing to about 70% at r=1-2 Mpc. The projected velocity dispersion in the Virgo-like cluster at R>~50 kpc is 300-600 km/s depending on orientation and R. Rotation is dynamically insignificant for the IC stars. The velocity distributions of IC stars and galaxies are in one cluster highly radially anisotropic, in the other close to isotropic.