Until recently , dust emission has been detected in very few host galaxies of gamma-ray bursts ( GRBHs ) .
With Herschel , we have now observed 17 GRBHs up to redshift z \sim 3 and detected seven of them at infrared ( IR ) wavelengths .
This relatively high detection rate ( 41 % ) may be due to the composition of our sample which at a median redshift of 1.1 is dominated by the hosts of dark GRBs .
Although the numbers are small , statistics suggest that dark GRBs are more likely to be detected in the IR than their optically-bright counterparts .
Combining our IR data with optical , near-infrared , and radio data from our own datasets and from the literature , we have constructed spectral energy distributions ( SEDs ) which span up to 6 orders of magnitude in wavelength .
By fitting the SEDs , we have obtained stellar masses , dust masses , star-formation rate ( SFR ) , and extinctions for our sample galaxies .
We find that GRBHs are galaxies that tend to have a high specfic SFR ( sSFR ) , and like other star-forming galaxies , their ratios of dust-to-stellar mass are well correlated with sSFR .
Dust masses of GRBHs relative to stellar mass and SFR fall within the range of other star-forming galaxies in the local universe , and of sub-millimeter galaxies ( SMGs ) and luminous IR galaxies for redshift z \ga 1 .
We incorporate our Herschel sample into a larger compilation of GRBHs , after checking for consistency in mass and SFR estimations .
This combined sample is compared to SFR-weighted median stellar masses of the widest , deepest galaxy survey to date in order to establish whether or not GRBs can be used as an unbiased tracer of cosmic comoving SFR density ( SFRD ) in the universe .
In contrast with previous results , this comparison shows that GRBHs are medium-sized galaxies with relatively high sSFRs , as might be expected for galaxies selected on the basis of SFR because of the explosive GRB event .
Stellar masses and sSFRs of GRBHs as a function of redshift are similar to what is expected for star-forming galaxy populations at similar redshifts .
We conclude that there is no strong evidence that GRBs are biased tracers of SFRD ; thus they should be able to reliably probe the SFRD to early epochs .