Metal Abundances and Star-Formation Rates of Emission-Line Galaxies in and around the Bootes Void

TL;DR

This study investigates whether galaxy metallicity and star-formation rates depend on local environment, finding no significant environmental influence within and around the Bootes Void, and confirming the mass-metallicity relation's role in observed trends.

Contribution

It provides the first detailed analysis of metallicity and SFR in galaxies within the Bootes Void, demonstrating environmental independence of these properties.

Findings

No dependence of metallicity and SFR on environment.

Weak trends are due to stellar mass effects.

Void galaxies have similar properties to those in denser regions.

Abstract

We explore the possible dependencies of galaxy metal abundance and star-formation rate (SFR) on local environment, focusing on the volume of space in and around the Bootes Void. Our sample of star-forming galaxies comes from the second catalog of the H-alpha-selected KPNO International Spectroscopic Survey (KISS) which overlaps the void. This sample represents a statistically complete, line-flux-limited ensemble of 820 star-forming galaxies, all of which possess metallicity and SFR estimates. We carry out two distinct analyses of the KISS galaxies: one which probes the properties of the entire sample as a function of local density, and a second which details the properties of 33 KISS star-forming galaxies located within the Bootes Void. In both cases we find no evidence that either the metallicity of the KISS galaxies or their SFRs depend on the environments within which the galaxies are located. Our global analysis does show weak trends for decreasing stellar mass, decreasing metallicity, and decreasing SFRs with decreasing local densities. However, we argue that the metallicity and SFR trends are artifacts of the stellar mass - local density trend. In particular, the change in metallicity with density is precisely what one would predict from the mass-metallicity relation given the observed drop in stellar mass with decreasing metallicity. Likewise, the SFR trend with density disappears when one instead considers the mass-normalized specific SFR. The KISS galaxies dwelling in the Bootes Void are found to have nearly identical metallicity and SFR properties to a matched comparison sample, despite the fact that the former are located in density environments that are, on average, more than 16 times lower.