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The Redshift Distribution of the TOUGH Survey

Published online by Cambridge University Press:  22 July 2013

P. Jakobsson ,
J. Hjorth ,
D. Malesani ,
J.P.U. Fynbo ,
N.R. Tanvir ,
B. Milvang-Jensen  and
T. Krühler
P. Jakobsson
Affiliation:
Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
J. Hjorth
Affiliation:
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
D. Malesani
Affiliation:
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
J.P.U. Fynbo
Affiliation:
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
N.R. Tanvir
Affiliation:
Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
B. Milvang-Jensen
Affiliation:
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
T. Krühler
Affiliation:
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
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Abstract

We present the redshift results from a Very Large Telescope (VLT) program aimed atoptimizing the legacy value of the Swift mission: to characterize ahomogeneous, X-ray selected, sample of 69 GRB host galaxies. Fifteen new redshifts havebeen secured, resulting in a 77% (53/69) redshift completion, making the survey the mostcomprehensive in terms of redshift completeness of any sample to the full Swiftdepth, available to date. We present the cumulative redshift distribution andderive a conservative, yet small, associated uncertainty. We constrain the fraction ofSwift GRBs at high redshift to a maximum of 14% (5%) forz > 6 (z > 7). The mean redshift of the hostsample is assessed to be . Using this more complete sample, we confirm previous findingsthat the GRB rate at high redshift () appears to be in excess of predictions based onassumptions that it should follow conventional determinations of the star formationhistory of the universe, combined with an estimate of its likely metallicity dependence.This suggests that either star formation at high redshifts has been significantlyunderestimated, for example due to a dominant contribution from faint, undetectedgalaxies, or that GRB production is enhanced in the conditions of early star formation,beyond those usually ascribed to lower metallicity.

Type
Research Article
Information
European Astronomical Society Publications Series , Volume 61: Gamma-ray Bursts: 15 Years of GRB Afterglows – Progenitors, Environments and Host Galaxies from the Nearby to the Early Universe , 2013 , pp. 397 - 401
Copyright
© EAS, EDP Sciences 2013

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