On the distribution of stellar masses in gamma-ray burst host galaxies
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 (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 = 0.45 Msun/Lsun. We find that the hosts are low M*, star-forming systems. The median M* in our sample (<M*> = 109.7 Msun) is lower than that of "field" galaxies (e.g., Gemini Deep Deep Survey). The range spanned by M* is 107 Msun < M* < 1011 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.