DISCOVERY OF A DAMPED Lyα ABSORBER AT z=3.3 ALONG A GALAXY SIGHT-LINE IN THE SSA22 FIELD

Using galaxies as background light sources to map the Ly alpha absorption lines is a novel approach to study Damped Ly alpha Absorbers (DLAs). We report the discovery of an intervening z = 3.335 +/- 0.007 DLA along a galaxy sight-line identified among 80 Lyman Break Galaxy (LBG) spectra obtained with our Very Large Telescope/Visible Multi-Object Spectrograph survey in the SSA22 field. The measured DLA neutral hydrogen (H-I) column density is log(N-H I/cm(-2)) = 21.68 +/- 0.17. The DLA covering fraction over the extended background LBG is >70% (2 sigma), yielding a conservative constraint on the DLA area of greater than or similar to 1 kpc(2). Our search for a counterpart galaxy hosting this DLA concludes that there is no counterpart galaxy with star formation rate larger than a few M-circle dot yr(-1), ruling out an unobscured violent star formation in the DLA gas cloud. We also rule out the possibility that the host galaxy of the DLA is a passive galaxy with M-* greater than or similar to 5 x 10(10) M-circle dot or a heavily dust-obscured galaxy with E(B - V) greater than or similar to 2. The DLA may coincide with a large-scale overdensity of the spectroscopic LBGs. The occurrence rate of the DLA is compatible with that of DLAs found in QSO sight-lines.