GRB 091127/SN 2009nz and the VLT/X-shooter spectroscopy of its host galaxy: probing the faint end of the mass-metallicity relation^⋆

¹ INAF, Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
e-mail: susanna.vergani@brera.inaf.it
² GEPI-Observatoire de Paris Meudon, 5 place Jules Jansen, 92195 Meudon, France
³ Laboratoire Astroparticule et Cosmologie, 10 rue A. Domon et L. Duquet, 75205 Paris Cedex 13, France
⁴ Instituto de Astrofísica de Andalucía (IAA-CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁵ Department of Physics, University of Warwick, Coventry, CV4 7AL, UK
⁶ Dipartimento di Fisica e Matematica, Università dell’Insubria, via Valleggio 7, 22100 Como, Italy
⁷ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
⁸ INAF, Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monte Porzio Catone, Rome, Italy
⁹ ASI-Science Data Center, via Galileo Galilei, 00044 Frascati, Italy
¹⁰ European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Santiago 19, Chile
¹¹ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura-Santiago, Chile
¹² INAF, IASF di Bologna, via Gobetti 101, 40129 Bologna, Italy
¹³ Service d’Astrophysique, DSM/IRFU/SAp, CEA-Saclay, 91191 Gif-sur-Yvette, France
¹⁴ Centre for Astrophysics and Cosmology, Science Institute, University of Iceland, Dunhagi 5, 107 Reykjavík, Iceland
¹⁵ Astronomical Institute Anton Pannekoek, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, The Netherlands
¹⁶ The Oskar Klein Centre, Department of Astronomy, AlbaNova, Stockholm University, 10691 Stockholm, Sweden
¹⁷ Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK

Received: 19 July 2011
Accepted: 14 September 2011

Abstract

We perform a detailed study of the gamma-ray burst GRB 091127/SN 2009nz host galaxy at z = 0.490 using the VLT/X-shooter spectrograph in slit and integral-field unit (IFU) mode. From the analysis of the optical and X-ray afterglow data obtained from ground-based telescopes and Swift-XRT, we confirm the presence of a bump associated with SN 2009nz and find evidence of a possible jet break in the afterglow lightcurve. The X-shooter afterglow spectra reveal several emission lines from the underlying host, from which we derive its integrated properties. These properties agree with those of previously studied GRB-SN hosts and, more generally, with those of the long GRB host population. We use the Hubble Space Telescope and ground-based images of the host to determine its stellar mass (M_⋆). Our results extend to lower M_⋆ values the M-Z plot derived for the sample of long GRB hosts at 0.3 < z < 1.0 adding new information to probe the faint end of the M-Z relation and the shift of the LGRB host M-Z relation from that found from emission-line galaxy surveys. Thanks to the IFU spectroscopy, we can build the two-dimensional (2D) velocity, velocity dispersion, and star formation rate (SFR) maps. They show that the host galaxy has perturbed rotation kinematics with evidence of a SFR enhancement consistent with the afterglow position.