THE OPTICALLY UNBIASED GAMMA-RAY BURST HOST (TOUGH) SURVEY. I. SURVEY DESIGN AND CATALOGS

By J. Hjorth, D. Malesani, P. Jakobsson, A. Jaunsen, Johan Peter Uldall Fynbo, J. Gorosabel, T. Krühler, A. Levan, M. Michałowski, B. Milvang-Jensen and 4 more. 2012

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Long-duration gamma-ray bursts (GRBs) are powerful tracers of star-forming galaxies. We have defined a homogeneous subsample of 69 Swift GRB-selected galaxies spanning a very wide redshift range. Special attention has been devoted to making the sample optically unbiased through simple and well-defined selection criteria based on the high-energy properties of the bursts and their positions on the sky. Thanks to our extensive follow-up observations, this sample has now achieved a comparatively high degree of redshift completeness, and thus provides a legacy sample, useful for statistical studies of GRBs and their host galaxies. In this paper, we present the survey design and summarize the 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 host galaxies for 80% of the GRBs in the sample, although only 42% have Ks-band detections, which confirms that GRB-selected host galaxies are generally blue. The sample is not uniformly blue, however, with two extremely red objects detected. Moreover, galaxies hosting GRBs with no optical/NIR afterglows, whose identification therefore relies on X-ray localizations, are significantly brighter and redder than those with an optical/NIR afterglow. This supports a scenario where GRBs occurring in more massive and dusty galaxies frequently suffer high optical obscuration. Our spectroscopic campaign has resulted in 77% now having redshift measurements, with a median redshift of 2.14 ± 0.18. TOUGH alone includes 17 detected z > 2 Swift GRB host galaxies suitable for individual and statistical studies—a substantial increase over previous samples. Seven hosts have detections of the Lyα emission line and we can exclude an early indication that Lyα emission is ubiquitous among GRB hosts, but confirm that Lyα is stronger in GRB-selected galaxies than in flux-limited samples of Lyman break galaxies.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/da7a4640f856d41659ec5fcffc145b69868bd1e7

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In Astronomy and Astrophysics

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Citations in the corpus

• A POPULATION OF MASSIVE, LUMINOUS GALAXIES HOSTING HEAVILY DUST-OBSCURED GAMMA-RAY BURSTS: IMPLICATIONS FOR THE USE OF GRBs AS TRACERS OF COSMIC STAR FORMATION (2013, methodology): “Additional spectroscopy of this object with FORS-2 and X-shooter on the VLT was conducted under the TOUGH program (Hjorth et al. 2012; Jakobsson et al. 2012; Krühler et al. 2012b).”
• The Observer's Guide to the Gamma-Ray Burst-Supernova Connection (2016, background): “However, more recently this previously quite uniform picture of GRB hosts became somewhat more diverse: several metal-rich GRB hosts were discovered [244, 247, 248], which revealed a population of red, high-mass, high-luminosity hosts that were mostly associated with dust-extinguished afterglows [24”
• The THESEUS space mission concept: science case, design and expected performances (2017, background): “However, their contribution will be visible as emission and absorption lines in the afterglow spectra (Hjorth et al., 2012; Savaglio et al., 2009), and therefore we will be able to measure their spectroscopic redshift.”
• Spectroscopy of superluminous supernova host galaxies. A preference of hydrogen-poor events for extreme emission line galaxies (2014, methodology): “The z 1 TOUGH sample consists of 12 hosts at a median redshift of z = 0.59 (i.e. it is more distant on average than the literature sample).”
• GRB hosts through cosmic time - VLT/X-Shooter emission-line spectroscopy of 96 γ-ray-burst-selected galaxies at 0.1 (2015, methodology): “This brings the redshift completeness of TOUGH to 87% (60 out of 69 events), with a median/average redshift of zmed = 2.10 ± 0.18 and zavg = 2.20 ± 0.17, respectively.”
• A NEW POPULATION OF ULTRA-LONG DURATION GAMMA-RAY BURSTS (2013, background): “Hjorth et al. (2012) find the host has R > 27.92.”