Sparse sampling, galaxy bias, and voids
  To study the impact of sparsity and galaxy bias on void statistics, we use a
single large-volume, high-resolution N-body simulation to compare voids in
multiple levels of subsampled dark matter, halo populations, and mock galaxies
from a Halo Occupation Distribution model tuned to different galaxy survey
densities. We focus our comparison on three key observational statistics:
number functions, ellipticity distributions, and radial density profiles. We
use the hierarchical tree structure of voids to interpret the impacts of
sampling density and galaxy bias, and theoretical and empirical functions to
describe the statistics in all our sample populations. We are able to make
simple adjustments to theoretical expectations to offer prescriptions for
translating from analytics to the void properties measured in realistic
observations. We find that sampling density has a much larger effect on void
sizes than galaxy bias. At lower tracer density, small voids disappear and the
remaining voids are larger, more spherical, and have slightly steeper profiles.
When a proper lower mass threshold is chosen, voids in halo distributions
largely mimic those found in galaxy populations, except for ellipticities,
where galaxy bias leads to higher values. We use the void density profile of
Hamaus et al. (2014) to show that voids follow a self-similar and universal
trend, allowing simple translations between voids studied in dark matter and
voids identified in galaxy surveys. We have added the mock void catalogs used
in this work to the Public Cosmic Void Catalog at http://www.cosmicvoids.net.
