The observed evolution of galaxy clustering versus epoch-dependent biasingmodels

We study the observed evolution of galaxy clustering as a function of redsh ift. 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 s imilar 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 g alaxies. 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 su rveys select different populations, which do not have the same clustering a mplitudes; and the Malmquist bias, which means that within a given survey t he more distant galaxies tend to have brighter absolute magnitudes, and so do not have the same clustering amplitude. We correct for the first two eff ects and discuss the implications of Malmquist bias on the interpretation o f the data at different z. We then compare the observed galaxy clustering w ith models for the evolution of clustering in some fixed cosmologies. Corre cting for the scale-dependence effect significantly reduces the discrepanci es 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 measu rements are compatible with the assumption of a much lower biasing level, w hich only shows a weak dependence on z. Present observations still do not p rovide a strong constraint because of the large uncertainties, but clear di stinctions will be possible when larger data sets from surveys in progress become available. Finally we propose a model-independent test that can be u sed to place a lower limit on the density parameter Omega(0).