Redshift-space effects in voids and their impact on cosmological tests.
  Part II: the void-galaxy cross-correlation function
  This is the second part of a thorough investigation of the redshift-space
effects that affect void properties and the impact they have on cosmological
tests. Here, we focus on the void-galaxy cross-correlation function,
specifically, on the projected versions that we developed in a previous work.
The pillar of the analysis is the one-to-one relationship between real and
redshift-space voids above the shot-noise level identified with a spherical
void finder. Under this mapping, void properties are affected by three effects:
(i) a systematic expansion as a consequence of the distortions induced by
galaxy dynamics, (ii) the Alcock-Paczynski volume effect, which manifests as an
overall expansion or contraction depending on the fiducial cosmology, and (iii)
a systematic off-centring along the line of sight as a consequence of the
distortions induced by void dynamics. We found that correlations are also
affected by an additional source of distortions: the ellipticity of voids. This
is the first time that distortions due to the off-centring and ellipticity
effects are detected and quantified. With a simplified test, we verified that
the Gaussian streaming model is still robust provided all these effects are
taken into account, laying the foundations for improvements in current models
in order to obtain unbiased cosmological constraints from spectroscopic
surveys. Besides this practical importance, this analysis also encodes key
information about the structure and dynamics of the Universe at the largest
scales. Furthermore, some of the effects constitute cosmological probes by
themselves, as is the case of the void ellipticity.
