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Long-duration gamma-ray bursts (GRBs) are powerful tracers of star-forminggalaxies. We have defined a homogeneous subsample of 69 Swift GRB-selectedgalaxies spanning a very wide redshift range. Special attention has beendevoted to making the sample optically unbiased through simple and well-definedselection criteria based on the high-energy properties of the bursts and theirpositions on the sky. Thanks to our extensive follow-up observations, thissample has now achieved a comparatively high degree of redshift completeness,and thus provides a legacy sample, useful for statistical studies of GRBs andtheir host galaxies. In this paper we present the survey design and summarizethe results of our observing program conducted at the ESO Very Large Telescope(VLT) aimed at obtaining the most basic properties of galaxies in this sample,including a catalog of R and Ks magnitudes and redshifts. We detect the hostgalaxies for 80 % of the GRBs in the sample, although only 42 % have Ks-banddetections, which confirms that GRB-selected host galaxies are generally blue.The sample is not uniformly blue, however, with two extremely red objectsdetected. Moreover, galaxies hosting GRBs with no optical/NIR afterglows, whoseidentification therefore relies on X-ray localizations, are significantlybrighter and redder than those with an optical/NIR afterglow. Our spectroscopiccampaign has resulted in 77 % now having redshift measurements, with a medianredshift of 2.14 +- 0.18. TOUGH alone includes 17 detected z > 2 Swift GRB hostgalaxies suitable for individual and statistical studies. Seven hosts havedetections of the Ly-alpha emission line and we can exclude an early indicationthat Ly-alpha emission is ubiquitous among GRB hosts, but confirm that Ly-alphais stronger in GRB-selected galaxies than in flux-limited samples of Lymanbreak galaxies.

The optically unbiased GRB host (TOUGH) survey. I. Survey design and catalogs