Galaxy peculiar velocities and evolution-bias

Galaxy-bias can be split into two components: a formation-bias based on the locations of galaxy creation, and an evolution-bias that details on their subsequent evolution. In this Letter, we consider evolution-bias in the peaks model. In this model, galaxy formation takes place at local maxima in the density field, and we analyse the subsequent peculiar motion of these galaxies in a linear model of structure formation. The peak restriction yields differences in the velocity distribution and correlation between the galaxy and the dark matter fields, which causes the evolution-bias component of the total bias to evolve in a scale-dependent way. This mechanism naturally gives rise to a change in shape between galaxy and matter correlation functions that depends on the mean age of the galaxy population. This model predicts that older galaxies would be more strongly biased on large scales compared to younger galaxies. Our arguments are supported by a Monte Carlo simulation of galaxy pairs propagated using the Zel'dovich approximation for describing peculiar galaxy motion.