HETDEX [OIII] Emitters I: A spectroscopically selected low-redshift population of low-mass, low-metallicity galaxies

TL;DR

This paper presents a spectroscopic survey of 17 low-metallicity, low-mass galaxies at z<0.1, revealing a population that bridges typical dwarf galaxies and extreme blueberry galaxies, highlighting the effectiveness of spectroscopic methods.

Contribution

The study introduces a spectroscopically selected sample of low-metallicity, low-mass galaxies, demonstrating the potential to discover such populations without photometric pre-selection.

Findings

Sample galaxies follow the mass-metallicity relation.

Galaxies exhibit specific star formation rates similar to blueberry galaxies.

Spectroscopic surveys effectively identify low-mass, low-metallicity galaxies.

Abstract

We assemble a sample of 17 low metallicity (7.45 < log(O/H)+12 < 8.12) galaxies with z < 0.1 found spectroscopically, without photometric pre-selection, in early data from the Hobby Eberly Telescope Dark Energy Experiment (HETDEX). Star forming galaxies that occupy the lowest mass and metallicity end of the mass-metallicity relation tend to be under sampled in continuum-based surveys as their spectra are typically dominated by emission from newly forming stars. We search for galaxies with high [OIII]$\lambda$5007 / [OII]$\lambda$3727, implying highly ionized nebular emission often indicative of low metallicity systems. With the Second Generation Low Resolution Spectrograph on the Hobby Eberly Telescope we acquired follow-up spectra, with higher resolution and broader wavelength coverage, of each low-metallicity candidate in order to confirm the redshift, measure the H$\alpha$ and [NII] line strengths and, in many cases, obtain deeper spectra of the blue lines. We find our galaxies are consistent with the mass-metallicity relation of typical low mass galaxies. However, galaxies in our sample tend to have similar specific star formation rates (sSFRs) as the incredibly rare "blueberry" galaxies found in (Yang et. al. 2017). We illustrate the power of spectroscopic surveys for finding low mass and metallicity galaxies and reveal that we find a sample of galaxies that are a hybrid between the properties of typical dwarf galaxies and the more extreme blueberry galaxies.