Testing Subhalo Abundance Matching in Cosmological Smoothed Particle
  Hydrodynamics Simulations
  Subhalo abundance matching (SHAM) is a technique for populating simulated
dark matter distributions with galaxies, assuming a monotonic relation between
a galaxy's stellar mass or luminosity and the mass of its parent dark matter
halo or subhalo. We examine the accuracy of SHAM in two cosmological SPH
simulations, one of which includes momentum-driven winds. The SPH simulations
indeed show a nearly monotonic relation between stellar mass and halo mass
provided that, for satellite galaxies, we use the mass of the subhalo at the
epoch when it became a satellite. In each simulation, the median relation for
central and satellite galaxies is nearly identical, though a somewhat larger
fraction of satellites are outliers. SHAM-assigned masses (at z=0-2),
luminosities (R-band at z=0), or star formation rates (at z=2) have a 68%
scatter of 0.09-0.15 dex relative to the true simulation values. When we apply
SHAM to the subhalo population of collisionless N-body simulation with the same
initial conditions as the SPH runs, we find generally good agreement for the
halo occupation distributions and halo radial profiles of galaxy samples
defined by thresholds in stellar mass. However, because a small fraction of SPH
galaxies suffer severe stellar mass loss after becoming satellites, SHAM
slightly overpopulates high mass halos; this effect is more significant for the
wind simulation, which produces galaxies that are less massive and more
fragile. SHAM recovers the two-point correlation function of the SPH galaxies
in the no-wind simulation to better than 10% at scales 0.1 < r < 10 Mpc/h. For
the wind simulation, agreement is better than 15% at r > 2 Mpc/h, but
overpopulation of massive halos increases the correlation function by a factor
of ~2.5 on small scales.
