Evolution of Cosmic Voids: Structure, Galaxies, and Dynamics

TL;DR

This study examines the evolution of cosmic voids from redshift 2.09 to the present, revealing their growth, galaxy population changes, and internal dynamics, with implications for galaxy formation models.

Contribution

It provides a comprehensive analysis of void evolution, combining simulation and observational data, and highlights discrepancies with current galaxy formation theories in underdense regions.

Findings

Void emptiness increases over time.

Galaxy luminosity functions evolve significantly.

Outward galaxy flows decrease toward low redshift.

Abstract

We investigate the structural, photometric, and dynamical evolution of cosmic voids and their galaxy populations from $z=2.09$ to the present, focusing on void size as a key evolutionary parameter. Using void catalogs from four Millennium Simulation snapshots and SDSS data at $z<0.04$, we perform a unified analysis of void demographics, galaxy properties, and internal kinematics. Our analysis reveals clear evidence that cosmic voids exhibit a significant evolutionary trend of becoming progressively emptier toward low redshift, accompanied by a marked decline in the brightness and clustering of their galaxy populations. The void galaxy luminosity function evolves significantly: $M^{*}$ fades and $\alpha$ flattens with time, with large voids hosting brighter, more rapidly evolving galaxies than small voids. Stacked density profiles exhibit a universal shape when scaled by void radius, deepening and building more pronounced walls toward $z=0$. Galaxy spatial distributions reveal persistent size-dependent segregation, with galaxies in large voids lying farther from the center and more strongly clustered. Dynamical analysis of simulations shows coherent outward flows in all voids, with amplitudes decreasing toward $z=0$, providing a physical basis for observed redshift-space distortions. Comparison with SDSS broadly confirms these evolutionary trends but uncovers a non-zero central galaxy population in observed voids -- absent in $\Lambda$CDM predictions -- that may challenge current galaxy formation models in extreme underdensities. Future comparisons with additional simulations and deeper high-redshift surveys will provide stronger tests of $\Lambda$CDM in the most underdense regions.