HETDEX Pilot Survey. VI. $[{\rm{O}}\,{\rm{III}}]$ Emitters and Expectations for a Local Sample of Star-forming Galaxies in HETDEX

Abstract

We assemble an unbiased sample of 29 galaxies with [O II] λ3727 and/or [O III] λ5007 detections at z < 0.15 from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) Pilot Survey (HPS). HPS finds galaxies without pre-selection based on their detected emission lines via integral field spectroscopy. Sixteen of these objects were followed up with the second-generation, low resolution spectrograph (LRS2) on the upgraded Hobby-Eberly Telescope. Oxygen abundances were then derived via strong emission lines using a Bayesian approach. We find most of the galaxies fall along the massmetallicity relation derived from photometrically selected star forming galaxies in the Sloan Digital Sky Survey (SDSS). However, two of these galaxies have low metallicity (similar to the very rare green pea galaxies in mass-metallicity space). The star formation rates of this sample fall in an intermediate space between the SDSS star forming main sequence and the extreme green pea galaxies. We conclude that spectroscopic selection fills part of the mass-metallicity-SFR phase space that is missed in photometric surveys with pre-selection like SDSS, i.e., we find galaxies that are actively forming stars but are faint in

Multi-epoch spectroscopy of Mg II broad absorption line transitions

“…The HET/LRS-2 data were processed with the LRS2 pipeline (Indahl et al 2019), which includes standard long-slit spectral extraction procedures, but does not yet include flux calibration. The lack of flux calibration for the HET/LRS2 spectra does not affect the identification of BAL disappearance or emergence.…”

Revisiting the Local Star-Forming Galaxies Observed in the HETDEX Pilot Survey

“…Recently, Indahl et al (2019) studied galactic gas metallicity using Bayesian parameter estimation. More specifically, they reported gas metallicities and star formation rates (SFRs) for 29 low-redshift (z < 0.15) galaxies, and they studied the distribution of those galaxies in mass-metallicity-SFR phase space.…”

“…In this way, they were able to explore for a new galaxy population that might have been missed in previous studies. Indahl et al (2019) determined the metallicities and the nebular emission-line color excesses E(B − V) using the strong-line method. They followed the approach of Grasshorn Gebhardt et al (2016), and they carried out parameter estimation by employing the Bayesian approach and the MCMC method.…”

“…However, I noticed three points that can be improved. First, Indahl et al (2019) adopted a relatively small uncertainty for the line-ratio calibration. This affects the uncertainties of the estimated model parameters, since Indahl et al (2019) included the scatter of the line ratio for a given metallicity as an uncertainty term in the likelihood.…”

“…First, Indahl et al (2019) adopted a relatively small uncertainty for the line-ratio calibration. This affects the uncertainties of the estimated model parameters, since Indahl et al (2019) included the scatter of the line ratio for a given metallicity as an uncertainty term in the likelihood. Second, reproducibility test with mock data, which is not mentioned in Indahl et al (2019), will help determine how reliable the obtained results are.…”