The Distribution of Satellite Galaxies in the IllustrisTNG100 Simulation

Abstract

Abstract We investigate the spatial distribution of the satellites of isolated host galaxies in the IllustrisTNG100 simulation. In agreement with a previous, similar analysis of the Illustris-1 simulation, the satellites are typically poor tracers of the mean host mass density. Unlike the Illustris-1 satellites, here the spatial distribution of the complete satellite sample is well fitted by an NFW profile; however, the concentration is a factor of ∼2 lower than that of the mean host mass density. The spatial distributions of the brightest 50% and faintest 50% of the satellites are also well fitted by NFW profiles, but the concentrations differ by a factor of ∼2. When the sample is subdivided by host color and luminosity, the number density profiles for blue satellites generally fall below the mean host mass density profiles, while the number density profiles for red satellites generally rise above the mean host mass density profiles. These opposite, systematic offsets combine to yield a moderately good agreement between the mean mass density profile of the brightest blue hosts and the corresponding number density profile of their satellites. Lastly, we subdivide the satellites according to the redshifts at which they joined their hosts. From this, we find that neither the oldest one-third of the satellites nor the youngest one-third of the satellites faithfully trace the mean host mass density.