Properties and Origin of Galaxy Velocity Bias in the Illustris Simulation

Understand

We use the hydrodynamical galaxy formation simulations from the Illustris suite to study the origin and properties of galaxy velocity bias, i.e., the difference between the velocity distributions of galaxies and dark matter inside halos.

• We find that galaxy velocity bias is a decreasing function of the ratio of galaxy stellar mass to host halo mass.
• In general, central galaxies are not at rest with respect to dark matter halos or the core of halos, with a velocity dispersion above 0.04 times that of the dark matter.
• The central galaxy velocity bias is found to be mostly caused by the close interactions between the central and satellite galaxies.