An investigation of the line of sight towards QSO PKS 0237−233★

Abstract

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 C iv 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 log NHI [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 (H i is 95 per cent ionized) and in a part of the gas of the sub-DLA at zabs = 1.6720. The C iv 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 C iv 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.