The Star Formation Rate in the Reionization Era as Indicated by Gamma-ray Bursts

TL;DR

This paper uses high-redshift gamma-ray bursts to estimate the cosmic star formation rate during the reionization era, finding consistency with galaxy-based measurements and supporting the idea that star formation alone reionized the Universe.

Contribution

It demonstrates that correcting for biases in GRB rates aligns star formation estimates with galaxy observations, supporting reionization by star formation in the early Universe.

Findings

GRB rate does not directly trace SFR without correction

Corrected SFR aligns with galaxy-based measurements at high redshift

Star formation between z=6 and 8 was sufficient for reionization

Abstract

High-redshift gamma-ray bursts (GRBs) offer an extraordinary opportunity to study aspects of the early Universe, including the cosmic star formation rate (SFR). Motivated by the two recent highest-z GRBs, GRB 080913 at z = 6.7 and GRB 090423 at z = 8.1, and more than four years of Swift observations, we first confirm that the GRB rate does not trace the SFR in an unbiased way. Correcting for this, we find that the implied SFR to beyond z = 8 is consistent with LBG-based measurements after accounting for unseen galaxies at the faint end of the UV luminosity function. We show that this provides support for the integrated star formation in the range 6 < z < 8 to have been alone sufficient to reionize the Universe.