Astronomy and Astrophysics – Astrophysics
Scientific paper
2008-07-22
Astron.Astrophys. 490 (2008) 45-59
Astronomy and Astrophysics
Astrophysics
16 pages, 10 figures. Accepted for publication in A&A. Typos corrected
Scientific paper
10.1051/0004-6361:200809896
The collapsar model predicts that the progenitors of Gamma-ray Bursts (GRBs) are metal poor in Fe group elements. The existence of low metallicity stellar populations could manifest itself through special characteristics of the immediate environment of the GRB site in the host galaxy. We analyse the strong emission lines from the sub-luminous host galaxy of GRB 980425, which showed the first connection with a supernova explosion (SN 1998bw). The host has a sufficient size to allow detailed resolved spectroscopy of individual HII regions and to look for regions with special properties close to the the GRB site. Using integral field spectroscopy with VIMOS we cover most of the high surface brightness part of the host including the HII region where the supernova and GRB occurred. The star formation rate, reddening, equivalent width and stellar mass in the GRB region is similar to other HII regions in the host. Extreme values arise in the only region that shows emission lines from Wolf-Rayet stars; a region that lies 800 pc in projection from the GRB site. Strong emission line diagnostics of all HII regions imply oxygen abundances between 0.3 and 0.8 solar with the lowest values arising in the WR and GRB regions. Comparing the measured emission line ratios for a sample of low redshift GRB hosts to theoretical models and to observations of field galaxies, we find that GRBs arise in a range of metallicity environments while the regions are consistently very young. The similar line ratios of GRB hosts compared to the WR region can arise in spatially unresolved galaxies with bright HII regions near the GRB location. (Abridged)
Christensen Lars Lindberg
Le Floc'h Emeric
Sollerman Jason
Thoene Christina C.
Vreeswijk Paul M.
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