Locally Biased Galaxy Formation and Large‐Scale Structure

We examine the influence of the morphology-density(MD) relation and a widerange of simple models for biased galaxy formation on statistical measures oflarge scale structure. We contrast the behavior of local biasing models, inwhich the efficiency of galaxy formation is determined by density, geometry, orvelocity dispersion of the local mass distribution, with that of non-localbiasing models, in which galaxy formation is modulated coherently over scaleslarger than the galaxy correlation length. If morphological segregation ofgalaxies is governed by a local MD relation, then the correlation function ofE/S0 galaxies should be steeper and stronger than that of spiral galaxies onsmall scales, as observed, while on large scales the correlation functions ofE/S0 and spiral galaxies should have the same shape but different amplitudes.Similarly, all of our local bias models produce scale-independent amplificationof the correlation function and power spectrum in the linear and mildlynon-linear regimes; only a non-local biasing mechanism can alter the shape ofthe power spectrum on large scales. Moments of the biased galaxy distributionretain the hierarchical pattern of the mass moments, but biasing alters thevalues and scale-dependence of the hierarchical amplitudes S3 and S4.Pair-weighted moments of the galaxy velocity distribution are sensitive to thedetails of the biasing prescription. The non-linearity of the relation betweengalaxy density and mass density depends on the biasing prescription and thesmoothing scale, and the scatter in this relation is a useful diagnostic of thephysical parameters that determine the bias. Although the sensitivity of galaxyclustering statistics to the details of biasing is an obstacle to testingcosmological models, it is an asset for testing galaxy formation theories.Comment: 47 pages including 17 Figures, submitted to Ap