We present a detailed analysis of three metal absorption systems observed in
the spectrum of the HDF-South quasar J2233-606 (z_em = 2.238), taking advantage
of new VLT-UVES high resolution data (R=45000, S/N = 40-60, \lambda\lambda
3050-10000 \AA). Three main components, spanning about 300 km/s, can be
individuated in the Lyman limit system at z~1.92. They show a surprisingly
large variation in metallicities, respectively ~1/500, 1/8 and 1/100 solar. The
large value found for the second component at z=1.9259, suggests that the line
of sight crosses a star-forming region. In addition, there is a definite
correlation between velocity position and ionisation state in this component,
which we interpret as a possible signature of an expanding H II region. The
systems at z~1.94 and z~1.87 have also high metallicity, ~1/4 and 1/3 solar. We
find that photoionisation and collisional ionisation are equal alternatives to
explain the high excitation phase revealed by O VI absorption, seen in these
two systems. From the width of the Si IV, C IV, Si III and C III lines in the
system at z~1.87, we can estimate the temperature of the gas to be log T ~ 4.7,
excluding collisional ionisation. Finally, we compute the Si IV/C IV ratio for
all Voigt profile components in a sample of log N(C IV) > 14 systems at z < 2.
The values show a dispersion of more than an order of magnitude and most of
them are much larger than what is observed for weaker systems. This is probably
an indication that high column density systems preferably originate in galactic
halos and are mostly influenced by local ionising sources.Comment: 11 pages, 11 figures, accepted by A&A main journa
