Metal Abundances and Star Formation Rates of Emission-line Galaxies in and around the Boötes Void

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 Boötes Void. Our sample of starforming galaxies comes from the second catalog of the Hα-selected KPNO International Spectroscopic Survey (KISS) which overlaps the void. This sample represents a statistically complete, line-fluxlimited 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 Boötes 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 Boötes 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.

Searches for Extremely Metal-poor Galaxies Using Arecibo Legacy Fast ALFA–Selected Dwarf Galaxies *

“…In particular, we utilized the lower signal-to-noise ALFALFA galaxies with the idea that, at any given distance, they would have lower H I masses than their main ALFALFA catalog counterparts. In addition, they were selected to be located in the low-density region in front of the PPS (e.g., Haynes & Giovanelli 1986), because some studies have suggested that void galaxies tend to preferentially have lower metal abundances (e.g., Pustilnik et al 2016;Kniazev et al 2018; but also see Wegner et al 2019).…”

Chameleon Screening in Cosmic Voids

“…While the vast majority of the voids have sizes near the middle of the mentioned range, there are examples of extremely large/small voids. As an example, the Bootes void is know as one of the largest objects in the Universe with an approximate radial size of 44-50 Mpc/h [43,44]. On the lower side of the size spectrum, mini-voids have been detected with sizes in the range of 0.7-3.5 Mpc/h [45,46].…”

The H$α$ Dots Survey. II. A Second List of Faint Emission-Line Objects

“…That is, for a given value of the [N II]λ6583/Hα ratio, the spread in [O III]λ5007/Hβ is larger than is typically seen in samples of ELGs. For example, comparison with Figure 1 in either Hirschauer et al (2018) or Wegner et al (2019), based on ELGs from the KISS objective-prism survey (Salzer et al 2000(Salzer et al , 2001Gronwall et al 2004), shows that many of the Hα Dots extend to much lower values of [O III]λ5007/Hβ. This is typically interpretted as an age effect, where lower excitation values indicate ionization from older stellar populations where the most massive O stars have already ended their lives.…”