Revealing the galaxy-halo connection in IllustrisTNG
  We use the IllustrisTNG (TNG) simulations to explore the galaxy-halo
connection as inferred from state-of-the-art cosmological,
magnetohydrodynamical simulations. With the high mass resolution and large
volume achieved by combining the 100 Mpc (TNG100) and 300 Mpc (TNG300) volumes,
we establish the mean occupancy of central and satellite galaxies and their
dependence on the properties of the dark matter haloes hosting them. We derive
best-fitting HOD parameters from TNG100 and TNG300 for target galaxy number
densities of $\bar{n}_g = 0.032\,h^3$Mpc$^{-3}$ and $\bar{n}_g =
0.016\,h^3$Mpc$^{-3}$, respectively, corresponding to a minimum galaxy stellar
mass of $M_\star\sim1.9\times10^9\,{\rm M}_\odot$ and
$M_\star\sim3.5\times10^9\,{\rm M}_\odot$, respectively, in hosts more massive
than $10^{11}\,{\rm M}_\odot$. Consistent with previous work, we find that
haloes located in dense environments, with low concentrations, later formation
times, and high angular momenta are richest in their satellite population. At
low mass, highly-concentrated haloes and those located in overdense regions are
more likely to contain a central galaxy. The degree of environmental dependence
is sensitive to the definition adopted for the physical boundary of the host
halo. We examine the extent to which correlations between galaxy occupancy and
halo properties are independent and demonstrate that HODs predicted by halo
mass and present-day concentration capture the qualitative dependence on the
remaining halo properties. At fixed halo mass, concentration is a strong
predictor of the stellar mass of the central galaxy, which may play a defining
role in the fate of the satellite population. The radial distribution of
satellite galaxies, which exhibits a universal form across a wide range of host
halo mass, is described accurately by the best-fit NFW density profile of their
host haloes.
