ON THE DISTRIBUTION OF STELLAR MASSES IN GAMMA-RAY BURST HOST GALAXIES

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 (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 M-circle dot/L-circle dot. We find that the hosts are low M-*, star-forming systems. The median M-* in our sample (< M-*>= 10(9.7) M-circle dot) is lower than that of field galaxies (e.g., Gemini Deep Deep Survey). The range spanned by M-* is 10(7) M-circle dot < M-* < 10(11) M-circle dot, while the range spanned by the dust-uncorrected UV SFR is 10(-2) M-circle dot yr(-1) < SFR < 10 M-circle dot 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