Dependence of halo bias on mass and environment

The simplest analyses of halo bias assume that halo mass alone determines halo clustering. However, if the large-scale environment is fixed, then halo clustering is almost entirely determined by environment, and is almost completely independent of halo mass. We show why. Our analysis is useful for studies that use the environmental dependence of clustering to constrain cosmological and galaxy formation models. It also shows why many correlations between galaxy properties and environment are merely consequences of the underlying correlations between haloes and their environments, and provides a framework for quantifying such inherited correlations.