Voids in the SDSS Galaxy Survey

TL;DR

This paper identifies and characterizes cosmic voids in SDSS galaxy data, revealing how void properties and galaxy characteristics vary with galaxy brightness and environment.

Contribution

It introduces a method for detecting arbitrary-shaped voids and analyzes their properties and galaxy distributions, highlighting differences between void and dense region galaxies.

Findings

Void volume increases with decreasing galaxy brightness limit.

Galaxies in voids are bluer and have higher star formation rates.

Void shapes are elongated and can change significantly.

Abstract

Using the method of searching for arbitrary shaped voids in the distribution of volume-limited samples of galaxies from the DR5 SDSS survey, we have identified voids and investigated their characteristics and the change in these characteristics with decreasing Mlim - the upper limit on the absolute magnitude of the galaxies involved in the construction of voids. The total volume of the 50 largest voids increases with decreasing Mlim with a break near Mr* = -20.44 for SDSS galaxies. The mean density contrast in voids increases with decreasing Mlim also with a weak break near M*. The exponent of the dependence of the volume of a void on its rank increases significantly with decreasing Mlim starting from Mlim ~ -20.4 in the characteristic range of volumes, which reflects the tendency for greater clustering of brighter galaxies. The galaxies mostly tend to concentrate toward the void boundaries and to avoid the central void regions. The axial ratios of the ellipsoids equivalent to the voids are, on average, retained with changing Mlim and correspond to elongated and nonoblate void shapes, but some of the voids can change their shape significantly. The void centers show correlations reflecting the correlations of the galaxy distribution on scales (35-70)/h Mpc. The galaxy distribution in the identified voids is nonrandom - groups and filaments can be identified. We have compared the properties of the galaxies in voids and galaxies in structures identified using the minimum spanning tree. A noticeable difference is observed in the mean color indices and star formation rates per unit stellar mass of the galaxies in dense regions (structures) - as expected, the galaxies in voids are, on average, bluer and have higher log(SFR/M_star). These tendencies become stronger toward the central void regions.