Void Galaxies Follow a Distinct Evolutionary Path in the Environmental COntext Catalog

TL;DR

This study investigates how void galaxies differ from non-void galaxies in properties like mass, color, and star formation, revealing that void galaxies are typically bluer, more gas-rich, and more star-forming, even at fixed mass and morphology.

Contribution

It provides the first detailed comparison of void and non-void galaxy properties controlling for mass and morphology, and demonstrates that simple galaxy-halo matching models can reproduce observed trends.

Findings

Void galaxies have lower baryonic masses than denser environment galaxies.

Void galaxies are bluer, more gas-rich, and have higher star formation rates at fixed mass.

Mock catalogs with galaxy assembly bias can replicate environmental trends observed in ECO.

Abstract

We measure the environmental dependence, where environment is defined by the distance to the third nearest neighbor, of multiple galaxy properties inside the Environmental COntext (ECO) catalog. We focus primarily on void galaxies, which we define as the $10 \%$ of galaxies having the lowest local density. We compare the properties of void and non-void galaxies: baryonic mass, color, fractional stellar mass growth rate (FSMGR), morphology, and gas-to-stellar-mass ratio (estimated from a combination of HI data and photometric gas fractions calibrated with the RESOLVE survey). Our void galaxies typically have lower baryonic masses than galaxies in denser environments, and they display the properties expected of a lower mass population: they have more late-types, are bluer, have higher FSMGR, and are more gas rich. We control for baryonic mass and investigate the extent to which void galaxies are different at fixed mass. Void galaxies are bluer, more gas-rich, and more star forming at fixed mass than non-void galaxies, which is a possible signature of galaxy assembly bias. Furthermore, we show that these trends persist even at fixed mass and morphology, and we find that voids host a distinct population of early-types that are bluer and more star-forming than the typical red and quenched early-types. In addition to these empirical observational results, we also present theoretical results from mock catalogs with built-in galaxy assembly bias. We show that a simple matching of galaxy properties to (sub)halo properties, such as mass and age, can recover the observed environmental trends in ECO galaxies.