Quantifying the coherent outflows of galaxies around voids in the SDSS DR7

TL;DR

This study detects and quantifies coherent galaxy outflows around cosmic voids in SDSS DR7 using a novel statistical test, providing insights into large-scale structure dynamics and cosmological parameters.

Contribution

It introduces a robust <|cos theta|> statistical method to measure redshift-space distortions caused by outflows around voids, confirming their presence across various void sizes.

Findings

Outflows are more prominent around larger voids.

The <|cos theta|> statistic deviates significantly from uniformity near void edges.

Results help constrain cosmological parameters like Omega_m and Sigma_8.

Abstract

We report the detection, with a high level of confidence, of coherent outflows around voids found in the seventh data release of the Sloan Digital Sky Survey (SDSS DR7). In particular, we developed a robust <|cos theta|> statistical test to quantify the strength of redshift-space distortions (RSD) associated with extended coherent velocity fields. We consistently find that the vector that joins void centers with galaxies that lie in shells around them is more likely to be perpendicular to the line-of-sight than parallel to it. This effect is clear evidence for the existence of outflows in the vicinity of voids. We show that the RSD exist for a wide range of void radius and shell thickness, but they are more evident in the largest voids in our sample. For instance, we find that the <|cos theta|> for galaxies located in shells within 2 h^-1 Mpc from the edge of voids larger than 15 h^-1 Mpc deviates 3.81sigma from uniformity. The measurements presented in this work provide useful information to constrain cosmological parameters, in particular Omega_m and Sigma_8.