Clues on void evolution II: Measuring density and velocity profiles on SDSS galaxy redshift space distortions

摘要

Using the redshift-space distortions of void-galaxy cross-correlationfunction we analyse the dynamics of voids embedded in different environments.We compute the void-galaxy cross-correlation function in the Sloan Digital SkySurvey (SDSS) in terms of distances taken along the line of sight and projectedinto the sky. We analyse the distortions on the cross-correlation isodensitylevels and we find anisotropic isocontours consistent with expansion for largevoids with smoothly rising density profiles and collapse for small voids withoverdense shells surrounding them. Based on the linear approach ofgravitational collapse theory we developed a parametric model of thevoid-galaxy redshift space cross-correlation function. We show that this modelcan be used to successfully recover the underlying velocity and densityprofiles of voids from redshift space samples. By applying this technique toreal data, we confirm the twofold nature of void dynamics: large voidstypically are in an expansion phase whereas small voids tend to be surroundedby overdense and collapsing regions. These results are obtained from the SDSSspectroscopic galaxy catalogue and also from semi-analytic mock galaxycatalogues, thus supporting the viability of the standard LCDM model toreproduce large scale structure and dynamics.