光学无偏GRB主机（TOUGH）调查。V. VLT/X-shooter辐射线红移对Z~2的雨燕伽玛暴的影响
The optically unbiased GRB host (TOUGH) survey. V. VLT/X-shooter emission-line redshifts for Swift GRBs at z~2
摘要：
我们提出了同时光学和近红外（NIR）光谱的19个雨燕伽玛暴宿主星系的VLT/X-shooter的目的是测量它们的红移。银河系是从光学无偏伽马射线暴宿主（TOUGH）调查（19个星系中的15个）中选出的，或者是因为它们的伽马射线暴没有明亮的光学余辉。在这里，我们提供了13个观测到的星系的发射线红移，亮度在F606 W> 27等和R=22.9等之间（中值R=24.6等）。所有的红移中值为z=2.1，TOUGH宿主的z=2.3。我们的新数据显着提高了TOUGH调查的红移完整性，现在为77%（69个GRB中的53个）。它们还提供了九个原型暗伽马射线暴的精确红移（例如，GRB 071021在z=2.452和080207在z=2.086），这是典型的GRB，其中红移是具有挑战性的，以获得通过余辉光谱。这建立了X-射手光谱学作为一个有效的工具，用于确定红移的微弱，恒星形成，高红移星系，如伽玛射线暴主机。因此，这是朝着消除伽马射线暴样品中由光学暗事件引起的偏差迈出的又一步，并为更好地理解伽马射线暴形成的条件提供了基础。例如，从X射线数据（N_{H,X}）测量的柱密度的分布与余辉的暗度密切相关，并且在由具有明亮光学余辉的爆发主导的样品中向低N_{H, X}值倾斜。
英文摘要：
We present simultaneous optical and near-infrared (NIR) spectroscopy of 19 Swift GRB host galaxies with 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 R=24.6 mag). The median redshift is z=2.1 for all, and z=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., GRBs 071021 at z=2.452 and 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 towards 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 (N_{H,X}), for example, is closely related to the darkness of the afterglow and skewed towards low N_{H, X} values in samples that are dominated by bursts with bright optical afterglows.
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