On the distribution of stellar masses in gamma-ray burst host galaxies

TL;DR

This study analyzes the stellar masses and star formation rates of 30 gamma-ray burst host galaxies using infrared and ultraviolet data, revealing they are generally low-mass, star-forming systems with dust extinction present in a quarter of the sample.

Contribution

It provides the first comprehensive analysis of stellar masses and star formation rates in GRB host galaxies using Spitzer data, highlighting their low mass and star-forming nature.

Findings

Median stellar mass of hosts is 10^9.7 Msun, lower than field galaxies.

Range of stellar masses spans from 10^7 to 10^11 Msun.

Dust extinction affects at least 25% of the hosts.

Abstract

We analyse Spitzer images of 30 long-duration gamma-ray burst (GRB) host galaxies. We estimate their total stellar masses (M*) based on the rest-frame K-band luminosities (L_Krest) and constrain their star formation rates (SFRs, not corrected for dust extinction) based on the rest-frame UV continua. Further, we compute a mean M*/L_Krest = 0.45 Msun/Lsun. We find that the hosts are low M*, star-forming systems. The median M* in our sample (<M*> = 10^9.7 Msun) is lower than that of "field" galaxies (e.g., Gemini Deep Deep Survey). The range spanned by M* is 10^7 Msun < M* < 10^11 Msun, while the range spanned by the dust-uncorrected UV SFR is 10^-2 Msun yr^-1 < SFR < 10 Msun yr^-1. There is no evidence for intrinsic evolution in the distribution of M* with redshift. We show that extinction by dust must be present in at least 25% of the GRB hosts in our sample and suggest that this is a way to reconcile our finding of a relatively lower UV-based, specific SFR (PHI = SFR/M*) with previous claims that GRBs have some of the highest PHI values. We also examine the effect that the inability to resolve the star-forming regions in the hosts has on PHI.