Halo mass and assembly history exposed in the faint outskirts: the stellar and dark matter haloes of Illustris galaxies

We use the Illustris Simulations to gain insight into the build-up of the outer, low-surface brightness regions which surround galaxies. We characterize the stellar haloes by means of the logarithmic slope of the spherically-averaged stellar density profiles, alphaSTARS at z=0, and we relate these slopes to the properties of the underlying Dark-Matter (DM) haloes, their central galaxies, and their assembly histories. We analyze a sample of ~5,000 galaxies resolved with more than 5x10^4 particles each, and spanning a variety of morphologies and halo masses (3x10^11 < Mvir < 10^14 Msun). We find a strong trend between stellar halo slope and total halo mass, where more massive objects have shallower stellar haloes than the less massive ones (-5.5 \pm 0.5 < alphaSTARS
Comment: 13 Pages, 8 Figures. Minor changes to match published version: MNRAS, 2014, 444, 237. The Illustris website can be found at http://www.illustris-project.org/