  How do observed voids relate to the underlying dark matter distribution? To
examine the spatial distribution of dark matter contained within voids
identified in galaxy surveys, we apply Halo Occupation Distribution models
representing sparsely and densely sampled galaxy surveys to a high-resolution
N-body simulation. We compare these galaxy voids to voids found in the halo
distribution, low-resolution dark matter, and high-resolution dark matter. We
find that voids at all scales in densely sampled surveys - and medium- to
large-scale voids in sparse surveys - trace the same underdensities as dark
matter, but they are larger in radius by ~20%, they have somewhat shallower
density profiles, and they have centers offset by ~0.4Rv rms. However, in
void-to-void comparison we find that shape estimators are less robust to
sampling, and the largest voids in sparsely sampled surveys suffer
fragmentation at their edges. We find that voids in galaxy surveys always
correspond to underdensities in the dark matter, though the centers may be
offset. When this offset is taken into account, we recover almost identical
radial density profiles between galaxies and dark matter. All mock catalogs
used in this work are available at http://www.cosmicvoids.net.
