Abstract
We perform a detailed study of the gamma-ray burst GRB091127/SN2009nz host galaxy at z=0.490 using the VLT/X-shooter spectrograph in slit and integral-field unit (IFU). 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 SN2009nz 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 are in agreement 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_star). Our results extend to lower M_star 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 2D velocity, velocity dispersion and star formation rate (SFR) maps. They show that the host galaxy has a perturbed rotation kinematics with evidence of a SFR enhancement consistent with the afterglow position.
Highlights
The association of long gamma-ray bursts (LGRBs) with broadlined type Ic supernovae (SNe) is well-established (e.g. Hjorth & Bloom 2011 and references therein; see GRB 060614: Della Valle et al 2006; Fynbo et al 2006; Gal-Yam et al 2006)
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
While the delay in the X-ray observations prevents us from studying the prompt/early emission characteristics as done in Starling et al (2011), we have confirmed the presence of a SN bump as reported by Cobb et al (2010) and we point out the presence of a possible jet break, showing that GRB 091127 follows the so-called Ghirlanda relation
Summary
The association of long gamma-ray bursts (LGRBs) with broadlined type Ic supernovae (SNe) is well-established (e.g. Hjorth & Bloom 2011 and references therein; see GRB 060614: Della Valle et al 2006; Fynbo et al 2006; Gal-Yam et al 2006). It has been shown that they are systematically offset to lower metallicities with respect to the mass-metallicity relation found from the surveys of emission-line galaxies (Han et al 2010; Levesque et al 2010; Mannucci et al 2011) To explain this behaviour and build a complete picture of galaxy evolution, it is important to increase the size of the LGRB host sample to confirm this result and to determine whether and how these galaxies evolve at higher redshift. Together with the analysis of the afterglow lightcurve, we present in this paper a detailed study of the host galaxy of GRB 091127 at z = 0.49044 associated with SN 2009nz (Cobb et al 2010; Berger et al 2011), carried out using VLT/X-shooter (D’Odorico et al 2004) echelle slit and IFU spectroscopy.
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