TY - JOUR
T1 - The Optically Unbiased GRB Host (TOUGH) Survey. V. VLT/X-shooter Emission-line Redshifts for Swift GRBs at z ~ 2
AU - Krühler, Thomas Christian
AU - Malesani, Daniele
AU - Milvang-Jensen, Bo
AU - Fynbo, Johan Peter Uldall
AU - Hjorth, Jens
AU - Jakobsson, Pall
AU - Levan, Andrew
AU - Sparre, Martin
AU - Tanvir, N.R.
AU - Watson, Darach Jafar
PY - 2012/10/10
Y1 - 2012/10/10
N2 - We present simultaneous optical and near-infrared (NIR) spectroscopy of 19 Swift γ-ray burst (GRB) host galaxies observed with the VLT/X-shooter with the aim of measuring their redshifts. Galaxies were selected from The Optically Unbiased GRB Host (TOUGH) survey (15 of the 19 galaxies) or because they hosted GRBs without a bright optical afterglow. Here we provide emission-line redshifts for 13 of the observed galaxies with brightnesses between F606W > 27 mag and R = 22.9 mag (median R̃ = 24.6mag). The median redshift is Z̃ = 2.1 for all hosts and z̃ = 2.3 for the TOUGH hosts. Our new data significantly improve the redshift completeness of the TOUGH survey, which now stands at 77% (53 out of 69 GRBs). They furthermore provide accurate redshifts for nine prototype dark GRBs (e.g., GRB 071021 at z = 2.452 and GRB 080207 at z = 2.086), which are exemplary of GRBs where redshifts are challenging to obtain via afterglow spectroscopy. This establishes X-shooter spectroscopy as an efficient tool for redshift determination of faint, star-forming, high-redshift galaxies such as GRB hosts. It is hence a further step toward removing the bias in GRB samples that is caused by optically dark events, and provides the basis for a better understanding of the conditions in which GRBs form. The distribution of column densities as measured from X-ray data (NH, X), for example, is closely related to the darkness of the afterglow and skewed toward low N H, X values in samples that are dominated by bursts with bright optical afterglows.
AB - We present simultaneous optical and near-infrared (NIR) spectroscopy of 19 Swift γ-ray burst (GRB) host galaxies observed with the VLT/X-shooter with the aim of measuring their redshifts. Galaxies were selected from The Optically Unbiased GRB Host (TOUGH) survey (15 of the 19 galaxies) or because they hosted GRBs without a bright optical afterglow. Here we provide emission-line redshifts for 13 of the observed galaxies with brightnesses between F606W > 27 mag and R = 22.9 mag (median R̃ = 24.6mag). The median redshift is Z̃ = 2.1 for all hosts and z̃ = 2.3 for the TOUGH hosts. Our new data significantly improve the redshift completeness of the TOUGH survey, which now stands at 77% (53 out of 69 GRBs). They furthermore provide accurate redshifts for nine prototype dark GRBs (e.g., GRB 071021 at z = 2.452 and GRB 080207 at z = 2.086), which are exemplary of GRBs where redshifts are challenging to obtain via afterglow spectroscopy. This establishes X-shooter spectroscopy as an efficient tool for redshift determination of faint, star-forming, high-redshift galaxies such as GRB hosts. It is hence a further step toward removing the bias in GRB samples that is caused by optically dark events, and provides the basis for a better understanding of the conditions in which GRBs form. The distribution of column densities as measured from X-ray data (NH, X), for example, is closely related to the darkness of the afterglow and skewed toward low N H, X values in samples that are dominated by bursts with bright optical afterglows.
U2 - 10.1088/0004-637X/758/1/46
DO - 10.1088/0004-637X/758/1/46
M3 - Journal article
SN - 0004-637X
VL - 758
SP - 46
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
ER -