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

TL;DR

This paper analyzes the dynamics of cosmic voids using SDSS galaxy redshift space distortions, developing a model to recover density and velocity profiles, confirming expansion for large voids and collapse for small ones within the LCDM framework.

Contribution

It introduces a parametric model for void-galaxy redshift space cross-correlation, enabling the recovery of void profiles and confirming the twofold nature of void dynamics in SDSS data.

Findings

Large voids are expanding, small voids are collapsing.

The model successfully recovers velocity and density profiles.

Results support the LCDM model's predictions.

Abstract

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.