Cosmic Emulation: Fast Predictions for the Galaxy Power Spectrum
  The halo occupation distribution (HOD) approach has proven to be an effective
method for modeling galaxy clustering and bias. In this approach, galaxies of a
given type are probabilistically assigned to individual halos in N-body
simulations. In this paper, we present a fast emulator for predicting the fully
nonlinear galaxy power spectrum over a range of freely specifiable HOD modeling
parameters. The emulator is constructed using results from 100 HOD models run
on a large LCDM N-body simulation, with Gaussian Process interpolation applied
to a PCA-based representation of the galaxy power spectrum. The total error is
currently ~3% (~2% in the simulation and ~1% in the emulation process) from z=1
to z=0, over the considered parameter range. We use the emulator to investigate
parametric dependencies in the HOD model, as well as the behavior of galaxy
bias as a function of HOD parameters. The emulator is publicly available at
http://www.hep.anl.gov/cosmology/CosmicEmu/emu.html.
