Gas inflow and outflow in an interacting high-redshift galaxy. The remarkable host environment of GRB 080810 at z = 3.35

We reveal multiple components of an interacting galaxy system at z ≈ 3.35 through a detailed analysis of the exquisite high-resolution Keck/HIRES spectrum of the afterglow of a gamma-ray burst (GRB). Through Voigt-profile fitting of absorption lines from the Lyman series, we constrain the neutral hydrogen column density to N<SUB>H i</SUB> ≤ 10<SUP>18.35</SUP> cm<SUP>-2</SUP> for the densest of four distinct systems at the host redshift of GRB 080810, which is among the lowest N<SUB>H i</SUB> ever observed in a GRB host, even though the line of sight passes within a projected 5 kpc of the galaxy centres. By detailed analysis of the corresponding metal absorption lines, we derive chemical, ionic, and kinematic properties of the individual absorbing systems, and thus build a picture of the host as a whole. Striking differences between the systems imply that the line of sight passes through several phases of gas: the star-forming regions of the GRB host; enriched material in the form of a galactic outflow; the hot and ionised halo of a second interacting galaxy falling towards the host at a line-of-sight velocity of 700 km s<SUP>-1</SUP>; and a cool metal-poor cloud that may represent one of the best candidates yet for the inflow of metal-poor gas from the intergalactic medium. The reduced spectrum is only available at the CDS via anonymous ftp to <A href='http://cdsarc.u-strasbg.fr'>http://cdsarc.u-strasbg.fr</A> (<A href='http://130.79.128.5'>http://130.79.128.5</A>) or via <A href='http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A107'>http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/607/A107</A>