The properties of the hot gas in galaxy groups and clusters from 1D hydrodynamical simulations .1. Cosmological infall models

We report the results of 1D hydrodynamical modelling of the evolution of gas in galaxy clusters. We have incorporated many of the effects missing from earlier 1D treatments: improved modelling of the dark matter and galaxy distributions, cosmologically realistic evolution of the cluster potential, and the effects of a multiphase cooling flow. The model utilizes a fairly standard 1D Lagrangian hydrodynamical code to calculate the evolution of the intracluster gas. This is coupled to a theoretical model for the growth of dark matter density perturbations. The main advantages of this treatment over 3D codes are (1) improved spatial resolution within the cooling flow region, (2) much faster execution time, allowing a fuller exploration of parameter space, and (3) the inclusion of additional physics. In the present paper, we explore the development of infall models - in which gas relaxes into a deepening potential well - covering a wide range of cluster mass scales. We find that such simple models reproduce many of the global properties of observed clusters. Very strong cooling flows develop in these 1D cluster models. In practice, disruption by major mergers probably reduces the cooling rate in most clusters. The models overpredict the gas fraction in low-mass systems, indicating the need for additional physical processes, such as pre-heating or galaxy winds, which become important on small mass scales.