The Effect of Baryons on the Dynamical-Friction Timescale of Merging Dark-Matter Halos

We show the effect that the baryonic center of a satellite galaxy can have on its decay time as it falls into a host galaxy. The concentrated baryonic presence in the center of the galaxy helps retain more mass in the inner regions of the galaxy, causing the tidal radius to increase, and thus changing the dynamical-friction timescale of the satellite galaxy as it falls into its host. We present an analytical calculation as well as N-body simulations showing that the dynamical-friction timescale of an infalling satellite galaxy is a strong function of its baryon-dark matter mass ratio, and changes at different rates depending on the density profile of the satellite galaxy. Therefore, calculations which only take the dark matter halo of a galaxy into account may significantly overestimate the decay timescale of an infalling galaxy.