THE OPTICALLY UNBIASED GRB HOST (TOUGH) SURVEY. VI. RADIO OBSERVATIONS AT z ≲ 1 AND CONSISTENCY WITH TYPICAL STAR-FORMING GALAXIES*

The objective of this paper is to determine the level of obscured star formation activity and dust attenuation in a sample of gamma-ray burst (GRB) hosts, and to test the hypothesis that GRB hosts have properties consistent with those of the general star-forming galaxy populations. We present a radio continuum survey of all z 500 M ☉ yr-1. For the undetected hosts the mean radio flux (<35 μJy 3σ) corresponds to an average SFR < 15 M ☉ yr-1. Moreover, gsim 88% of the z lsim 1 GRB hosts have ultraviolet dust attenuation A UV < 6.7 mag (visual attenuation AV < 3 mag). Hence, we did not find evidence for large dust obscuration in a majority of GRB hosts. Finally, we found that the distributions of SFRs and A UV of GRB hosts are consistent with those of Lyman break galaxies, Hα emitters at similar redshifts, and of galaxies from cosmological simulations. The similarity of the GRB population with other star-forming galaxies is consistent with the hypothesis that GRBs, a least at z lsim 1, trace a large fraction of all star formation, and are therefore less biased indicators than once thought.