On the Dynamical Origin of Bias in Clusters of Galaxies
  We study the effect of the dynamical friction induced by the presence of substructure on the statistics of the collapse of density peaks. Applying the results of a former paper we show that within high density environments, like rich clusters of galaxies, the collapse of smaller peaks is strongly delayed until very late epochs. A bias of dynamical nature thus naturally arises because high density peaks preferentially collapse For a standard CDM model we find that this dynamical bias can account for a substantial part of the total bias required by observations on cluster scales. 
S. Colafrancesco, V. Antonuccio-Delogu and A. Del Popolo