Simulating galaxy clusters - I. Thermal and chemical properties of the intracluster medium

We have performed a series of N-body/hydrodynamical (TREESPH) simulations of clusters and groups of galaxies, selected from a cosmological volume within a Lambda cold dark matter (Lambda CDM) framework: these objects have been resimulated at higher resolution to z = 0, in order to follow also the dynamical, thermal and chemical input on to the intracluster medium (ICM) from stellar populations within galaxies. The simulations include metallicity-dependent radiative cooling, star formation according to different initial mass functions ( IMFs), energy feedback as strong starburst-driven galactic superwinds, chemical evolution with non-instantaneous recycling of gas and heavy elements, effects of a metagalactic ultraviolet ( UV) field and thermal conduction in the ICM. In this paper, the first in a series of three, we derive results, mainly at z = 0, on the temperature and entropy profiles of the ICM, its X-ray luminosity, the cluster cold components [cold fraction as well as mass-to-light ratio (MLR)] and the metal distribution between ICM and stars. In general, models with efficient superwinds ( produced by the action of supernovae and, in some simulations, of active galactic nuclei (AGNs), along with a top-heavy stellar IMF, are able to reproduce fairly well the observed LX-T relation, the entropy profiles and the cold fraction: both features are found to be needed in order to remove high-density and low-entropy cold gas at core scales, although additional alternative feedback mechanisms would still be required to prevent late-time central cooling flows, and subsequent overproduction of stars and heavy elements at the centre. Observed radial ICM temperature profiles can be matched, except for the gradual decline in temperature inside r similar to 0.1R(vir). Metal enrichment of the ICM gives rise to somewhat steep inner iron gradients; yet, the global level of enrichment compares well to observational estimates when a top-heavy IMF is adopted, and after correcting for the stars formed at late times at the base of the cooling flows, the metal partition between stars and ICM gets into good agreement with observations. The overall abundance and profile of iron in the ICM is found essentially unchanged from z = 1 to present time. Finally, the alpha/Fe of the gas is found to increase steadily with radius, decreasing over time.