2004A&A...419..927V

We present photometry and spectroscopy of the afterglow of GRB030323. VLT spectra of the afterglow show damped Lyα (DLA) absorption and low- and high-ionization lines at a redshift z=3.3718±0.0005. The inferred neutral hydrogen column density, logN(HI)=21.90±0.07, is larger than any (GRB- or QSO-) DLA HI column density inferred directly from Lyα in absorption. From the afterglow photometry, we derive a conservative upper limit to the host-galaxy extinction: A_V<0.5mag. The iron abundance is [Fe/H]=-1.47±0.11, while the metallicity of the gas as measured from sulphur is [S/H]=-1.26±0.20. We derive an upper limit on the H₂ molecular fraction of 2N(H₂)/(2N(H₂)+N(HI))≲10^–6. In the Lyα trough, a Lyα emission line is detected, which corresponds to a star-formation rate (not corrected for dust extinction) of roughly 1M_☉/yr. All these results are consistent with the host galaxy of GRB030323 consisting of a low metallicity gas with a low dust content. We detect fine-structure lines of silicon, SiII*, which have never been clearly detected in QSO-DLAs; this suggests that these lines are produced in the vicinity of the GRB explosion site. Under the assumption that these fine-structure levels are populated by particle collisions, we estimate the HI volume density to be n_HI=10²-10⁴cm^–3. HST/ACS imaging 4 months after the burst shows an extended AB(F606W)=28.0±0.3mag object at a distance of 0.14" (1kpc) from the early afterglow location, which presumably is the host galaxy of GRB030323.