The observed evolution of galaxy clustering versus epoch-dependent biasing models

We study the observed evolution of galaxy clustering as a function of redshift. We find that the clustering of galaxies, parametrized by the amplitude of fluctuations in the distribution of galaxies at a comoving scale of 8 h(-1) Mpc, decreases as we go from observations of the local Universe to z similar to 2. On the other hand, clustering of the Lyman-break galaxies at z similar to 3 is very strong, comparable to the clustering of present-day galaxies. However, there are three major factors to take into account while comparing clustering measurements coming from various surveys: the so-called 'scale-dependence' effect, caused by measurements being made at different scales; the 'type-selection' effect introduced by the fact that different galaxy surveys select different populations, which do not have the same clustering amplitudes; and the Malmquist bias, which means that within a given survey the more distant galaxies tend to have brighter absolute magnitudes, and so do not have the same clustering amplitude. We correct for the first two effects and discuss the implications of Malmquist bias on the interpretation of the data at different z. We then compare the observed galaxy clustering with models for the evolution of clustering in some fixed cosmologies. Correcting for the scale-dependence effect significantly reduces the discrepancies between different measurements. We interpret the observed clustering signal at high redshift as coming from objects that are highly biased with respect to the underlying distribution of mass; this is not the case for z less than or similar to 2, where measurements are compatible with the assumption of a much lower biasing level, which only shows a weak dependence on z. Present observations still do not provide a strong constraint because of the large uncertainties, but clear distinctions will be possible when larger data sets from surveys in progress become available. Finally we propose a model-independent test that can be used to place a lower limit on the density parameter Omega(0).