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Issue A&A
Volume 406, Number 3, August II 2003
Page(s) L63 - L66
Section Letters
DOI 10.1051/0004-6361:20030931



A&A 406, L63-L66 (2003)
DOI: 10.1051/0004-6361:20030931

Letter

On the Ly $\alpha$ emission from gamma-ray burst host galaxies: Evidence for low metallicities

J. P. U. Fynbo1, 2, P. Jakobsson2, P. Møller3, J. Hjorth2, B. Thomsen1, M. I. Andersen4, A. S. Fruchter5, J. Gorosabel6, 5, S. T. Holland7, C. Ledoux8, H. Pedersen2, J. Rhoads5, M. Weidinger1 and R. A. M. J. Wijers9

1  Department of Physics and Astronomy, University of Aarhus, Ny Munkegade, 8000 Århus C, Denmark
2  Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen Ø, Denmark
3  European Southern Observatory, Karl Schwarzschild-Strasse 2, 85748 Garching, Germany
4  Astrophysikalisches Institut, 14482 Potsdam, Germany
5  Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
6  Instituto de Astrofísica de Andalucía (IAA-CSIC), PO Box 03004, 18080 Granada, Spain
7  Department of Physics, University of Notre Dame, Notre Dame, IN 46556-5670, USA
8  European Southern Observatory, Casilla 19001, Santiago 19, Chile
9  University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

(Received 30 April 2003 / Accepted 19 June 2003)

Abstract
We report on the results of a search for Ly $\alpha$ emission from the host galaxy of the z=2.140 GRB 011211 and other galaxies in its surrounding field. We detect Ly $\alpha$ emission from the host as well as from six other galaxies in the field. The restframe equivalent width of the Ly $\alpha$ line from the GRB 011211 host is about 21 Å. This is the fifth detection of Ly $\alpha$ emission out of five possible detections from GRB host galaxies, strongly indicating that GRB hosts, at least at high redshifts, are Ly $\alpha$ emitters. This is intriguing as only ~25% of the Lyman-Break selected galaxies at similar redshifts have Ly $\alpha$ emission lines with restframe equivalent width larger than 20 Å. Possible explanations are i) a preference for GRB progenitors to be metal-poor as expected in the collapsar model, ii) an optical afterglow selection bias against dusty hosts, and iii) a higher fraction of Ly $\alpha$ emitters at the faint end of the luminosity function for high- z galaxies. Of these, the current evidence seems to favour i).


Key words:  gamma rays: bursts -- galaxies: high redshift -- techniques: photometric

Offprint request: J. P. U. Fynbo, jfynbo@phys.au.dk

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© ESO 2003


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