Partly based on observations collected at the European Southern Observatory under ESO proposal No. 082.A-0693.
Supersolar metal abundances in two galaxies at z ∼ 3.57 revealed by the GRB 090323 afterglow spectrum★
Article first published online: 5 DEC 2011
© 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS
Monthly Notices of the Royal Astronomical Society
Volume 420, Issue 1, pages 627–636, February 2012
How to Cite
Savaglio, S., Rau, A., Greiner, J., Krühler, T., McBreen, S., Hartmann, D. H., Updike, A. C., Filgas, R., Klose, S., Afonso, P., Clemens, C., Küpcü Yoldaş, A., Olivares E., F., Sudilovsky, V. and Szokoly, G. (2012), Supersolar metal abundances in two galaxies at z ∼ 3.57 revealed by the GRB 090323 afterglow spectrum. Monthly Notices of the Royal Astronomical Society, 420: 627–636. doi: 10.1111/j.1365-2966.2011.20074.x
- Issue published online: 23 JAN 2012
- Article first published online: 5 DEC 2011
- Accepted 2011 October 25. Received 2011 October 21; in original form 2011 June 10
- gamma-ray burst: individual: GRB 090323;
- galaxies: ISM;
- cosmology: observations
We report on the surprisingly high metallicity measured in two absorption systems at high redshift, detected in the Very Large Telescope spectrum of the afterglow of the gamma-ray burst (GRB) GRB 090323. The two systems, at redshift z= 3.5673 and 3.5774 (separation Δv≈ 660 km s−1), are dominated by the neutral gas in the interstellar medium of the parent galaxies. From the singly ionized zinc and sulphur, we estimate oversolar metallicities of [Zn/H] =+0.29 ± 0.10 and [S/H] = +0.67 ± 0.34, in the blue and red absorber, respectively. These are the highest metallicities ever measured in galaxies at z > 3. We propose that the two systems trace two galaxies in the process of merging, whose star formation and metallicity are heightened by the interaction. This enhanced star formation might also have triggered the birth of the GRB progenitor. As typically seen in star-forming galaxies, the fine-structure absorption Si ii* is detected, both in z= 3.5774 ± 0.0005 and 3.5673 ± 0.0003. From the rest-frame ultraviolet emission in the GRB location, we derive a relatively high, not corrected for dust extinction, star formation rate ≈6 M⊙ yr−1. These properties suggest a possible connection between some high-redshift GRB host galaxies and high-z massive submillimetre galaxies, which are characterized by disturbed morphologies and high metallicities. Our result provides additional evidence that the dispersion in the chemical enrichment of the Universe at high redshift is substantial, with the existence of very metal-rich galaxies less than two billion years after the big bang.