Clues on void evolution II: Measuring density and velocity profiles on
  SDSS galaxy redshift space distortions
  Using the redshift-space distortions of void-galaxy cross-correlation
function we analyse the dynamics of voids embedded in different environments.
We compute the void-galaxy cross-correlation function in the Sloan Digital Sky
Survey (SDSS) in terms of distances taken along the line of sight and projected
into the sky. We analyse the distortions on the cross-correlation isodensity
levels and we find anisotropic isocontours consistent with expansion for large
voids with smoothly rising density profiles and collapse for small voids with
overdense shells surrounding them. Based on the linear approach of
gravitational collapse theory we developed a parametric model of the
void-galaxy redshift space cross-correlation function. We show that this model
can be used to successfully recover the underlying velocity and density
profiles of voids from redshift space samples. By applying this technique to
real data, we confirm the twofold nature of void dynamics: large voids
typically are in an expansion phase whereas small voids tend to be surrounded
by overdense and collapsing regions. These results are obtained from the SDSS
spectroscopic galaxy catalogue and also from semi-analytic mock galaxy
catalogues, thus supporting the viability of the standard LCDM model to
reproduce large scale structure and dynamics.
