A nearby GRB host galaxy: VLT/X-shooter observations of HG 031203

摘要

Context. Long-duration gamma-ray bursts (LGRBs), which release enormous amounts of energy into the interstellar medium, occur in galaxies of generally low metallicity. For a better understanding of this phenomenon, detailed observations of the specific properties of the host galaxies (HG) and the environment near the LGRBs are mandatory. Aims. We aim at a spectroscopic analysis of HG 031203, the host galaxy of a LRGB burst, to obtain its properties. Our results will be compared with those of previous studies and the properties of a sample of luminous compact emission-line galaxies (LCGs) selected from SDSS DR7. Methods. Based on VLT/X-shooter spectroscopic observations taken from commissioning mode in the wavelength range ?~λλ3200–24?000??, we use standard direct methods to evaluate physical conditions and element abundances. The resolving power of the instrument also allowed us to trace the kinematics of the ionised gas. Furthermore, we use X-shooter data together with Spitzer observations in the mid-infrared range for testing hidden star formation. Results. We derive an interstellar oxygen abundance of 12 + log O/H = 8.20 ?±? 0.03 for HG 031203. The observed fluxes of hydrogen lines correspond to the theoretical recombination values after correction for extinction with a single value C(Hβ) = 1.67. We produce the CLOUDY photoionisation H ii region model that reproduces observed emission-line fluxes of different ions in the optical range. This model also predicts emission-line fluxes in the near-infrared (NIR) and mid-infrared (MIR) ranges that agree well with the observed ones. This implies that the star-forming region observed in the optical range is the only source of ionisation and there is no additional source of ionisation seen in the NIR and MIR ranges that is hidden in the optical range. We find the composite kinematic structure from profiles of the strong emission lines by decomposing them into two Gaussian narrow and broad components. These components correspond to two H ii regions, separated by ?~34 km s-1, and have full widths at half maximum (FWHM) ?~? 115 and ?~270?km?s-1, respectively. We find that the heavy element abundances, extinction-corrected Hα luminosity L(Hα)?= 7.27 ?×? 1041?erg?s-1, stellar mass M??=?2.5?×?108???M⊙, star-formation rate SFR(Hα) = 5.74 M⊙ yr-1 and specific star-formation rate SSFR(Hα) = 2.3??×? 10-8 yr-1 of HG 031203 are in the range that is covered by the LCGs. This implies that the LCGs with extreme star-formation that also comprise green pea galaxies as a subclass may harbour GRBs.