Issue |
A&A
Volume 490, Number 1, October IV 2008
|
|
---|---|---|
Page(s) | 45 - 59 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:200809896 | |
Published online | 18 August 2008 |
IFU observations of the GRB 980425/SN 1998bw host galaxy: emission line ratios in GRB regions *
1
European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: lichrist@eso.org
2
Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Ø, Denmark
3
Department of Astronomy, AlbaNova, 106 91 Stockholm University, Sweden
4
Spitzer Fellow, Institute for Astronomy, 2680 Woodlawn Drive, Honolulu HI 96822, USA
5
University of Leicester, University Road, Leicester, LE1 7RH, UK
Received:
3
April
2008
Accepted:
16
July
2008
Context. 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 in the characteristics of the GRB site immediate environment in the host galaxy.
Aims. 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 is of sufficient size to
allow detailed resolved spectroscopy of individual regions and to search for regions with peculiar properties close to
the the GRB site.
Methods. Using integral field spectroscopy with VIMOS we study most of the
high surface brightness part of the host including the region where the supernova and GRB occurred.
Results. The star formation rate, reddening, equivalent width and stellar mass
in the GRB region is similar to other regions in the
host. Extreme values arise in the only region that shows emission
lines from Wolf-Rayet stars, a region that is located 800 pc in
projection from the GRB site. Strong emission line diagnostics of
all
regions imply oxygen abundances between 0.3 and 0.8 solar with the lowest values arising in the WR and GRB regions.
Including uncertainties from the metallicity diagnostics, all
metallicities are similar to within 3σ. We demonstrate that
there is a good agreement between the luminosity weighted and mass
weighted specific star formation rates (SSFR) in individual young
regions. While the global average of the SSFR is
similar to high redshift GRB hosts, there are significant variations
between individual resolved
regions. Comparing the
measured emission line ratios of low redshift GRB hosts to
theoretical models and observations of field galaxies, we find that
GRBs are present in different environment metallicities while the
regions of their origin are consistently very young. Similar line
ratios of GRB hosts compared with those of the WR region can arise
in spatially unresolved galaxies with bright
regions
close to the GRB location.
Key words: gamma rays: bursts / galaxies: abundances / galaxies: individual: GRB 980425
© ESO, 2008
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