GRB091127/SN2009nz and the VLT/X-shooter spectroscopy of its host galaxy: probing the faint end of the mass-metallicity relation

TL;DR

This study uses VLT/X-shooter spectroscopy to analyze the host galaxy of GRB091127/SN2009nz at z=0.490, revealing its properties, kinematics, and extending the mass-metallicity relation to lower stellar masses.

Contribution

It provides new measurements of a GRB host galaxy at lower stellar mass, extending the mass-metallicity relation and analyzing its kinematics with IFU spectroscopy.

Findings

Host galaxy has perturbed rotation and enhanced star formation.

Results extend the M-Z relation to lower stellar masses.

Host properties align with typical long GRB host characteristics.

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.