EULERIAN BIAS AND THE GALAXY DENSITY FIELD

We investigate the effects on cosmological clustering statistics of em pirical biasing, where the galaxy distribution is a local transformati on of the present-day Eulerian density field. The effects of the suppr ession of galaxy numbers in voids, and their enhancement in regions of high density, are considered, independently and in combination. We co mpare results from numerical simulations with the predictions of simpl e analytic models. We find that the bias is generally scale-dependent, so that the shape of the galaxy power spectrum differs from that of t he underlying mass distribution. The degree of bias is always a monoto nic function of scale, tending to an asymptotic value on scales where the density fluctuations are linear. The scale dependence is often rat her weak, with many reasonable prescriptions giving a bias which is ne arly independent of scale. We have investigated whether such an Euleri an bias can reconcile a range of theoretical power spectra with the tw in requirements of fitting the galaxy power spectrum and reproducing t he observed mass-to-light ratios in clusters. It is not possible to sa tisfy these constraints for any member of the family of CDM-like power spectra in an Einstein-de Sitter universe when normalized to match CO BE on large scales and galaxy cluster abundances on intermediate scale s. We discuss what modifications of the mass power spectrum might prod uce agreement with the observational data.