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

Abstract

We analyze 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 (LKrest ) 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*/ LKrest = 0.45M⊙/L⊙. We find that the hosts are low M*, star-forming systems. The median M* in our sample ( = 109.7M⊙) is lower than that of "field" galaxies (e.g., Gemini Deep Deep Survey). The range spanned by M* is 107M⊙ < M* < 1011M⊙, while the range spanned by the dust-uncorrected UV SFR is 10-2M⊙ yr-1 < SFR < 10M⊙ 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 (ø = SFR/M *) with previous claims that GRBs have some of the highest ø values. We also examine the effect that the inability to resolve the star-forming regions in the hosts has on ø © 2010. The American Astronomical Society. All rights reserved.