Spitzer Observations of Gamma-Ray Burst Host Galaxies: A Unique Window into High Redshift Chemical Evolution and Star-formation

TL;DR

This study uses deep Spitzer observations of z~5 gamma-ray burst host galaxies to explore their luminosity, star-formation rates, and metallicity evolution, revealing insights into high-redshift galaxy properties and chemical evolution.

Contribution

It provides the first measurements of luminosity and star-formation rates of z~5 GRB hosts, linking GRB rates to galaxy evolution and metallicity changes over cosmic time.

Findings

z~5 GRB hosts are less luminous than typical galaxies at similar redshifts.

Star-formation rate density at z~4.5 and z~6 is estimated from GRB rates.

Metallicity of star-forming galaxies decreases with redshift, indicating metal loss to the intergalactic medium.

Abstract

We present deep Spitzer 3.6 micron observations of three z~5 GRB host galaxies. Our observations reveal that z~5 GRB hosts are a factor of 3 less luminous than the median rest-frame V-band luminosity of spectroscopically confirmed z~5 galaxies in the GOODS fields and the UDF. The strong connection between GRBs and massive star formation implies that not all star-forming galaxies at these redshifts are currently being accounted for in deep surveys and GRBs provide a unique way to measure the contribution to the star-formation rate density from galaxies at the faint end of the galaxy luminosity function. By correlating the co-moving star-formation rate density with co-moving GRB rates at lower redshifts, we estimate a lower limit to the star-formation rate density of 0.12+/-0.09 and 0.09+/-0.05 M_sun/yr/Mpc^3 at z~4.5 and z~6, respectively. Finally, we provide evidence that the average metallicity of star-forming galaxies evolves as (stellar mass density)^(0.69+/-0.17) between $z\sim5$ and $z\sim0$, probably indicative of the loss of a significant fraction of metals to the intergalactic medium, particularly in low-mass galaxies.