Far-infrared star-formation rates of six GRB host galaxies with ALMA

TL;DR

This study uses ALMA far-infrared observations of six high-redshift GRB host galaxies to accurately determine their star-formation rates, revealing the importance of FIR data in understanding galaxy properties and potential biases in previous estimates.

Contribution

First FIR observations of six IR-bright GRB host galaxies with detailed SED analysis, highlighting the significance of FIR data for accurate SFR estimation and galaxy characterization.

Findings

Five hosts do not require AGN components in SED fits.

Star-formation rates are higher than previous estimates.

Rest-frame FIR data are crucial for accurate SFR measurements.

Abstract

Gamma-Ray Bursts (GRBs) can be a promising tracer of cosmic star-formation rate history (CSFRH). In order to reveal the CSFRH using GRBs, it is important to understand whether they are biased tracers or not. For this purpose, it is crucial to understand properties of GRB host galaxies, in comparison to field galaxies. In this work, we report ALMA far-infrared (FIR) observations of six $z\sim2$ IR-bright GRB host galaxies, which are selected for the brightness in IR. Among them, four host galaxies are detected for the first time in the rest-frame FIR. In addition to the ALMA data, we collected multi-wavelength data from previous studies for the six GRB host galaxies. Spectral energy distribution (SED) fitting analyses were performed with \texttt{CIGALE} to investigate physical properties of the host galaxies, and to test whether active galactic nucleus (AGN) and radio components are required or not. Our results indicate that the best-fit templates of five GRB host galaxies do not require an AGN component, suggesting the absence of AGNs. One GRB host galaxy, 080207, shows a very small AGN contribution. While derived stellar masses of the three host galaxies are mostly consistent with those in previous studies, interestingly the value of star-formation rates (SFRs) of all six GRB hosts are inconsistent with previous studies. Our results indicate the importance of rest-frame FIR observations to correctly estimate SFRs by covering thermal emission from cold dust heated by star formation.