The redshift selected sample of long gamma-ray burst host galaxies: the overall metallicity distribution at $z < 0.4$

TL;DR

This study analyzes the metallicity distribution of low-redshift long gamma-ray burst host galaxies, finding that models with a metallicity cutoff best match observations and discussing potential sampling biases.

Contribution

It provides the first comprehensive metallicity distribution for low-redshift long GRB hosts and constrains the metallicity dependence of GRB production.

Findings

Models with a metallicity cutoff around 12+log(O/H) ∼ 8.3 fit the observed data.

No-metallicity-dependence models are inconsistent with the observations.

Sample biases may affect the observed distribution, as discussed with the GRB 111225A host galaxy.

Abstract

We discuss the host galaxy metallicity distribution of all long gamma-ray bursts (GRBs) whose redshifts are known to be $< 0.4$, including newly obtained spectroscopic datasets of the host galaxies of GRB 060614, 090417B, and 130427A. We compare the metallicity distribution of the low-redshift sample to the model predictions, and constrain the relation between metallicity and GRB occurrence. We take account of spatial variation of metallicities among star forming regions within a galaxy. We found that the models, in which only low-metallicity stars produce GRBs with a sharp cutoff of GRB production efficiency around 12+log(O/H) $\sim$ 8.3, can well reproduce the observed distribution, while the models with no metallicity dependence are not consistent with the observations. We also discuss possible sampling biases we may suffer by collecting long GRBs whose redshifts are known, presenting the photometric observations of the host galaxy of GRB 111225A at $z = 0.297$ whose redshift has been undetermined until $\sim$ 2.3 years after the burst.