  We present a method for creating simulated galaxy catalogs with realistic
galaxy luminosities, broad-band colors, and projected clustering over large
cosmic volumes. The technique, denoted ADDGALS (Adding Density Dependent
GAlaxies to Lightcone Simulations), uses an empirical approach to place
galaxies within lightcone outputs of cosmological simulations. It can be
applied to significantly lower-resolution simulations than those required for
commonly used methods such as halo occupation distributions, subhalo abundance
matching, and semi-analytic models, while still accurately reproducing
projected galaxy clustering statistics down to scales of r ~ 100 kpc/h. We show
that \addgals\ catalogs reproduce several statistical properties of the galaxy
distribution as measured by the Sloan Digital Sky Survey (SDSS) main galaxy
sample, including galaxy number densities, observed magnitude and color
distributions, as well as luminosity- and color-dependent clustering. We also
compare to cluster-galaxy cross correlations, where we find significant
discrepancies with measurements from SDSS that are likely linked to artificial
subhalo disruption in the simulations. Applications of this model to
simulations of deep wide-area photometric surveys, including modeling
weak-lensing statistics, photometric redshifts, and galaxy cluster finding are
presented in DeRose et al (2019), and an application to a full cosmology
analysis of Dark Energy Survey (DES) Year 3 like data is presented in DeRose
etl al (2021). We plan to publicly release a 10,313 square degree catalog
constructed using ADDGALS with magnitudes appropriate for several existing and
planned surveys, including SDSS, DES, VISTA, WISE, and LSST.
