Supersolar metal abundances in two galaxies at z ∼ 3.57 revealed by the GRB090323 afterglow spectrum

S. Savaglio, A. Rau, J. Greiner, T. Krühler, S. Mcbreen, D. H. Hartmann, A. C. Updike, R. Filgas, S. Klose, P. Afonso, C. Clemens, A. Küpcü Yoldaş, F. Olivares E., V. Sudilovsky, G. Szokoly

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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) GRB090323. The two systems, at redshift z= 3.5673 and 3.5774 (separation Δv≈ 660kms-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 Siii* 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 ≈6Myr-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.

Original languageEnglish
Pages (from-to)627-636
Number of pages10
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - Feb 1 2012



  • Cosmology: observations
  • Galaxies: ISM
  • Gamma-ray burst: individual: GRB090323

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

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., & Szokoly, G. (2012). Supersolar metal abundances in two galaxies at z ∼ 3.57 revealed by the GRB090323 afterglow spectrum. Monthly Notices of the Royal Astronomical Society, 420(1), 627-636.