An investigation of the line of sight towards QSO PKS 0237-233

TL;DR

This study provides a detailed analysis of absorption systems along the line of sight to QSO PKS 0237-233, revealing complex ionization and abundance properties, and concludes that the observed CIV overdensity is likely due to chance rather than a supercluster.

Contribution

It offers a comprehensive high-resolution spectral analysis of multiple absorption systems, including accurate abundance measurements and ionization modeling, clarifying the nature of the CIV overdensity.

Findings

No evidence for a supercluster; overdensity likely due to chance.

Ionization effects are significant in some absorption systems.

Accurate elemental abundances measured for sub-DLAs.

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 (SNR) ~ 60-80 obtained with the Ultraviolet and Visual Echelle Spectrograph mounted on the Very Large Telescope. 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 z_abs = 1.6359 (with two components of logN(HI) = 18.45, 19.05) and z_abs = 1.6720 (logN(H I) = 19.78) sub-Damped Ly-alpha 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 onto 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 z_abs = 1.6359 (HI is 95 percent ionized) and in part of the gas of the sub-DLA at z_abs = 1.6359. 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.