Shredded Galaxies as the Source of Diffuse Intrahalo Light on Varying Scales

Abstract

We make predictions for diffuse stellar mass fractions in dark matter halos\nfrom the scales of small spiral galaxies to those of large galaxy clusters. We\nuse an extensively-tested analytic model for subhalo infall and evolution and\nempirical constraints from galaxy survey data to set the stellar mass in each\naccreted subhalo to model diffuse light. We add stellar mass to the diffuse\nlight as subhalos become disrupted due to interactions within their host halos.\nWe predict that the stellar mass fraction in diffuse, intrahalo light should\nrise on average from ~0.5% to approximately 20% from small galaxy halos to poor\ngroups. The trend with mass flattens considerably beyond the group scale,\nincreasing weakly from a fraction of ~20% in poor galaxy clusters (~10^14\nM_sun) to roughly ~30% in massive clusters (~10^15 M_sun). The mass-dependent\ndiffuse light fraction is governed primarily by the empirical fact that the\nmass-to-light ratio in galaxy halos must vary as a function of halo mass.\nGalaxy halos have little diffuse light because they accrete most of their mass\nin small subhalos that themselves have high mass-to-light ratios; stellar halos\naround galaxies are built primarily from disrupted dwarf-irregular-type\ngalaxies with M*~10^8.5 M_sun. The diffuse light in group and cluster halos is\nbuilt from satellite galaxies that form stars efficiently and have\ncorrespondingly low mass-to-light ratios; intracluster light is dominated by\nmaterial liberated from massive galaxies with M*~10^11 M_sun. Our results are\nconsistent with existing observations spanning the galaxy, group, and cluster\nscale; however, they can be tested more rigorously in future deep surveys for\nfaint diffuse light.\n