Parameter tests within cosmological simulations of galaxy formation

Numerical simulations of galaxy formation require a number of parameters. S ome of these are intrinsic to the numerical integration scheme (e.g., the t ime-step), while others describe the physical model (e.g., the gas metallic ity), III this paper we present results of a systematic exploration of the effects of varying a subset of these parameters on simulations of galaxy fo rmation. We use N-body and 'Smoothed Particle Hydrodynamics' techniques to follow the evolution of cold dark matter and gas in a small volume. We comp are a fiducial model with 24 different simulations, in which one parameter at a time is varied, focusing on properties such as the relative fraction o f hot and cold gas, and the abundance and masses of galaxies. We find that for reasonable choices of numerical values, many parameters have relatively little effect on the galaxies, with the notable exception of the parameter s that control the resolution of the simulation and the efficiency with whi ch gas cools.