Letter to the Editor

On the Lyα emission from gamma-ray burst host galaxies: Evidence for low metallicities ^*,**

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

Corresponding author: J. P. U. Fynbo, jfynbo@phys.au.dk

Received: 30 April 2003
Accepted: 19 June 2003

Abstract

We report on the results of a search for Lyα emission from the host galaxy of the  GRB 011211 and other galaxies in its surrounding field. We detect Lyα emission from the host as well as from six other galaxies in the field. The restframe equivalent width of the Lyα line from the GRB 011211 host is about 21 Å. This is the fifth detection of Lyα emission out of five possible detections from GRB host galaxies, strongly indicating that GRB hosts, at least at high redshifts, are Lyα emitters. This is intriguing as only ~25% of the Lyman-Break selected galaxies at similar redshifts have Lyα 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 Lyα emitters at the faint end of the luminosity function for high-z galaxies. Of these, the current evidence seems to favour i).