TY - JOUR
T1 - The low-extinction afterglow in the solar-metallicity host galaxy of γ -ray burst 110918A
AU - Elliott, J.
AU - Krühler, T.
AU - Greiner, J.
AU - Savaglio, S.
AU - Olivares, F.
AU - Rau, E. A.
AU - De Ugarte Postigo, A.
AU - Sánchez-Ramírez, R.
AU - Wiersema, K.
AU - Schady, P.
AU - Kann, D. A.
AU - Filgas, R.
AU - Nardini, M.
AU - Berger, E.
AU - Fox, D.
AU - Gorosabel, J.
AU - Klose, S.
AU - Levan, A.
AU - Nicuesa Guelbenzu, A.
AU - Rossi, A.
AU - Schmidl, S.
AU - Sudilovsky, V.
AU - Tanvir, N. R.
AU - Thöne, C. C.
N1 - Funding Information:
We thank the anonymous referees for their constructive criticisms, Régis Lachaume for the WFI observations, and Mara Salvato and Ivan Baldry for helpful discussions. Part of the funding for GROND (both hardware as well as personnel) was generously granted from the Leibniz-Prize to Prof. G. Hasinger (DFG grant HA 1850/28-1). Based on observations made with the Gran Telescopio Canarias (GTC), that is installed in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias on the island of La Palma. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. A.d.U.P. acknowledges support from a Marie Curie Career Integration Grant Fellowship. T.K. acknowledges support by the European Commission under the Marie Curie Intra-European Fellowship Programme. The Dark Cosmology Centre is funded by the Danish National Research Foundation. SS acknowledges support through project M.FE.A.Ext 00003 of the MPG. F.O.E. acknowledges funding of his Ph.D. through the Deutscher Akademischer Austausch-Dienst (DAAD). A.d.U.P., C.T., R.S.R., and J.G. acknowledge support from the Spanish research projects AYA2012-39362-C02-02, AYA2011-24780/ESP, AYA2009-14000-C03-01/ESP, and AYA2010-21887-C04-01. A.d.U.P. acknowledges support from The Dark Cosmology Centre. K.W. acknowledges support by the STFC. P.S. acknowledges support by DFG grant SA 2001/1-1. D.A.K. acknowledges support by the DFG cluster of excellence Origin and Structure of the Universe. S.K., A.N.G., and A.R. acknowledge support by DFG grant Kl 766/16-1. A.R., A.N.G., A.K., and D.A.K. are grateful for travel funding support through MPE. M.N. acknowledges support by DFG grant SA 2001/2-1. E.B. acknowledges support from the National Science Foundation through Grant AST-1107973. J.E. is thankful for the support from A. and G. Elliott.
PY - 2013
Y1 - 2013
N2 - Galaxies selected through long γ-ray bursts (GRBs) could be of fundamental importance when mapping the star formation history out to the highest redshifts. Before using them as efficient tools in the early Universe, however, the environmental factors that govern the formation of GRBs need to be understood. Metallicity is theoretically thought to be a fundamental driver in GRB explosions and energetics, but it is still, even after more than a decade of extensive studies, not fully understood. This is largely related to two phenomena: a dust-extinction bias, which prevented high-mass and thus likely high-metallicity GRB hosts from being detected in the first place, and a lack of efficient instrumentation, which limited spectroscopic studies, including metallicity measurements, to the low-redshift end of the GRB host population. The subject of this work is the very energetic GRB 110918A (E γ,iso = 1.9 × 1054 erg), for which we measure a redshift of z = 0.984. GRB 110918A gave rise to a luminous afterglow with an intrinsic spectral slope of β = 0.70, which probed a sight-line with little extinction (AGRBV = 0.16 magAVGRB=0.16 mag) and soft X-ray absorption (NH,X = (1.6 ± 0.5) × 1021 cm-2) typical of the established distributions of afterglow properties. However, photometric and spectroscopic follow-up observations of the galaxy hosting GRB 110918A, including optical/near-infrared photometry with the Gamma-Ray burst Optical Near-infrared Detector and spectroscopy with the Very Large Telescope/X-shooter, reveal an all but average GRB host in comparison to the z ∼1 galaxies selected through similar afterglows to date. It has a large spatial extent with a half-light radius of R1/2 ∼10R1210 kpc, the highest stellar mass for z < 1.9 (log (M -/M⊙) = 10.68 ± 0.16), and an Hα-based star formation rate of SFRHα = 41 +28-16SFRHα=41-16+28 M ⊙ yr-1. We measure a gas-phase extinction of AgasV ∼1.8 magAVgas1.8 mag through the Balmer decrement and one of the largest host-integrated metallicities ever of around solar using the well-constrained ratios of [N ii]/Hα and [N ii]/[O ii] (12 + log (O/H) = 8.93 ± 0.13 and 8.85+0.14 -0.188.85-0.18+0.14, respectively). This presents one of the very few robust metallicity measurements of GRB hosts at z ∼1, and establishes thatGRB hosts at z ∼1 can also be very metal rich. It conclusively rules out a metallicity cut-off in GRB host galaxies and argues against an anti-correlation between metallicity and energy release in GRBs.
AB - Galaxies selected through long γ-ray bursts (GRBs) could be of fundamental importance when mapping the star formation history out to the highest redshifts. Before using them as efficient tools in the early Universe, however, the environmental factors that govern the formation of GRBs need to be understood. Metallicity is theoretically thought to be a fundamental driver in GRB explosions and energetics, but it is still, even after more than a decade of extensive studies, not fully understood. This is largely related to two phenomena: a dust-extinction bias, which prevented high-mass and thus likely high-metallicity GRB hosts from being detected in the first place, and a lack of efficient instrumentation, which limited spectroscopic studies, including metallicity measurements, to the low-redshift end of the GRB host population. The subject of this work is the very energetic GRB 110918A (E γ,iso = 1.9 × 1054 erg), for which we measure a redshift of z = 0.984. GRB 110918A gave rise to a luminous afterglow with an intrinsic spectral slope of β = 0.70, which probed a sight-line with little extinction (AGRBV = 0.16 magAVGRB=0.16 mag) and soft X-ray absorption (NH,X = (1.6 ± 0.5) × 1021 cm-2) typical of the established distributions of afterglow properties. However, photometric and spectroscopic follow-up observations of the galaxy hosting GRB 110918A, including optical/near-infrared photometry with the Gamma-Ray burst Optical Near-infrared Detector and spectroscopy with the Very Large Telescope/X-shooter, reveal an all but average GRB host in comparison to the z ∼1 galaxies selected through similar afterglows to date. It has a large spatial extent with a half-light radius of R1/2 ∼10R1210 kpc, the highest stellar mass for z < 1.9 (log (M -/M⊙) = 10.68 ± 0.16), and an Hα-based star formation rate of SFRHα = 41 +28-16SFRHα=41-16+28 M ⊙ yr-1. We measure a gas-phase extinction of AgasV ∼1.8 magAVgas1.8 mag through the Balmer decrement and one of the largest host-integrated metallicities ever of around solar using the well-constrained ratios of [N ii]/Hα and [N ii]/[O ii] (12 + log (O/H) = 8.93 ± 0.13 and 8.85+0.14 -0.188.85-0.18+0.14, respectively). This presents one of the very few robust metallicity measurements of GRB hosts at z ∼1, and establishes thatGRB hosts at z ∼1 can also be very metal rich. It conclusively rules out a metallicity cut-off in GRB host galaxies and argues against an anti-correlation between metallicity and energy release in GRBs.
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U2 - 10.1051/0004-6361/201220968
DO - 10.1051/0004-6361/201220968
M3 - Article
AN - SCOPUS:84880673322
SN - 0004-6361
VL - 556
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A23
ER -