The host of GRB 030323 at : A very high column density DLA system with a low metallicity ^*

¹ European Southern Observatory, Alonso de Córdova 3107, Casilla 19001, Santiago 19, Chile
² P. Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
³ Astronomical Institute “Anton Pannekoek”, University of Amsterdam & Center for High Energy Astrophysics, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands
⁴ Department of Physics and Astronomy, Århus University, Ny Munkegade, 8000 Århus C, Denmark
⁵ Niels Bohr Institute, Astronomical Observatory, Copenhagen University, Juliane Mariesvej 30, 2100 København Ø, Denmark
⁶ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁷ Universities Space Research Association / US Naval Observatory Flagstaff Station, PO Box 1149, Flagstaff AZ 86002-1149, USA
⁸ Physics Department, University of Rome “Tor Vergata", Via della Ricerca Scientifica 1, 00133 Rome, Italy
⁹ Department of Physical Sciences, University of Hertfordshire, College Lane, Hatfield, Herts AL10 9AB, UK
¹⁰ Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH, UK
¹¹ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218-2463, USA
¹² Instituto de Astrofísica de Andalucía (IAA-CSIC), Apartado de Correos, 3004, 18080 Granada, Spain
¹³ NSSTC, SD-50, 320 Sparkman Dr., Huntsville, AL 35805, USA
¹⁴ Istituto di Astrofisica Spaziale e Fisica Cosmica – Sezione di Bologna, CNR, via Gobetti 101, 40129 Bologna, Italy
¹⁵ INAF – Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
¹⁶ Department of Physics and Astronomy, University of Canterbury, Christchurch, New Zealand
¹⁷ Joint Astronomy Centre, 660 N, A'ohoku Place, Hilo, Hawaii, HI 96720, USA
¹⁸ Department of Physics & Astronomy, Clemson University, Clemson, SC 29634-0978, USA

Corresponding author: P. M. Vreeswijk, pvreeswi@eso.org

Received: 17 July 2003
Accepted: 27 February 2004

Abstract

We present photometry and spectroscopy of the afterglow of GRB 030323. VLT spectra of the afterglow show damped Lyα (DLA) absorption and low- and high-ionization lines at a redshift . The inferred neutral hydrogen column density, , is larger than any (GRB- or QSO-) DLA column density inferred directly from Lyα in absorption. From the afterglow photometry, we derive a conservative upper limit to the host-galaxy extinction:  mag. The iron abundance is , while the metallicity of the gas as measured from sulphur is . We derive an upper limit on the H₂ molecular fraction of . In the Lyα trough, a Lyα emission line is detected, which corresponds to a star-formation rate (not corrected for dust extinction) of roughly 1 M yr^-1. All these results are consistent with the host galaxy of GRB 030323 consisting of a low metallicity gas with a low dust content. We detect fine-structure lines of silicon, *, 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 volume density to be  cm^-3. HST/ACS imaging 4 months after the burst shows an extended  mag object at a distance of 014 (1 kpc) from the early afterglow location, which presumably is the host galaxy of GRB 030323.