Rapid Simulations of Halo and Subhalo Clustering
  The analysis of cosmological galaxy surveys requires realistic simulations
for their interpretation. Forward modelling is a powerful method to simulate
galaxy clustering without the need for an underlying complex model. This
approach requires fast cosmological simulations with a high resolution and
large volume, to resolve small dark matter halos associated to single galaxies.
In this work, we present fast halo and subhalo clustering simulations based on
the Lagrangian perturbation theory code PINOCCHIO, which generates halos and
merger trees. The subhalo progenitors are extracted from the merger history and
the survival of subhalos is modelled. We introduce a new fitting function for
the subhalo merger time, which includes an additional dependence on subhalo
mass. The spatial distribution of subhalos within their hosts is modelled using
a number density profile. We compare our simulations with the halo finder
Rockstar applied to the full N-body code GADGET-2. We find a good agreement for
the number ratio of subhalos, for halo masses down to $5.7 \cdot 10^9$
M$_\odot$/h. The subhalo mass function and the correlation function of halos
and subhalos are also in good agreement. We investigate the effect of the
chosen number density profile on the resulting subhalo clustering. Our
simulation is approximate yet realistic and significantly faster compared to a
full N-body simulation combined with a halo finder. The fast halo and subhalo
clustering simulations offer good prospects for galaxy forward models using
subhalo abundance matching.
