2013MNRAS.435.1727F

We present a detailed analysis of absorption systems along the line of sight towards QSO PKS 0237-233 using a high-resolution spectrum of signal-to-noise ratio ∼ 60-80 obtained with the Ultraviolet and Visual Echelle Spectrograph mounted on the Very Large Telescope (VLT/UVES). This line of sight is known to show a remarkable overdensity of Civ systems that has been interpreted as revealing the presence of a supercluster of galaxies. A detailed analysis of each of these absorption systems is presented. In particular, for the zabs = 1.6359 (with two components of logNHI [cm-2] = 18.45, 19.05) and zabs = 1.6720 (log NHI = 19.78) sub-damped Lyα systems (sub-DLAs), we measure accurate abundances (resp. [O/H] = -1.63±0.07 and [Zn/H] = -0.57±0.05 relative to solar). While the depletion of refractory elements on to dust grains in both sub-DLAs is not noteworthy, photoionization models show that ionization effects are important in a part of the absorbing gas of the sub-DLA at zabs = 1.6359 (Hi is 95 percent ionized) and in a part of the gas of the sub-DLA at zabs = 1.6720. The Civ clustering properties along the line of sight is studied in order to investigate the nature of the observed overdensity. We conclude that despite the unusually high number of Civ systems detected along the line of sight, there is no compelling evidence for the presence of a single unusual overdensity and that the situation is consistent with chance coincidence.