GRB 050223: A dark GRB in a dusty starburst galaxy
  Aims: We aim at detecting and determining the properties of the host galaxy of the dark GRB 050223.   Methods: We use VLT optical/NIR images coupled to Swift X-ray positioning, and optical spectra of the host galaxy to measure its properties.   Results: We find a single galaxy within the Swift error box of GRB 050223. It is located at z = 0.584 and its luminosity is L ~ 0.4 L*. Emission lines in the galaxy spectrum imply an intrinsic SFR > 7 Msun/yr, and a large extinction A_V > 2 mag within it. We also detect absorption lines, which reveal an underlying stellar population with an age between 40 Myr and 1.5 Gyr.   Conclusions: The identification of a host galaxy with atypical properties using only the X-ray transient suggests that a bias may be present in the former sample of host galaxies. Dust obscuration together with intrinsic faintness are the most probable causes for the darkness of this burst. 
L. J. Pellizza (1 and 2), P.-A. Duc (1), E. Le Floc'h (3 and 4), I. F.   Mirabel (5), L. A. Antonelli (6), S. Campana (7), G...