We studied the clustering of metal absorption lines and the structures that they arise in as a function of cosmic time. We focused on the behaviour of ̧iv and ionic species. These ̧iv and absorption features are identified along a given quasar sightline. We exploited the two-point correlation function (2PCF) to investigate the clustering of these structures as a function of their separation. We utilised the E-XQR-30 data to perform a novel analysis at z>5. We also drew on literature surveys (including XQ-100) of lower redshift quasars to investigate the possible evolution of this clustering towards cosmic noon (i. e. z∼ 2-3). We find no significant evolution with redshift when considering the separation of absorbers in velocity space. Since we were comparing data across a large interval of cosmic time, we also considered the separation between absorbers in the reference frame of physical distances. In this reference frame, we find that the amplitude of the clustering increases with cosmic time for both ̧iv and on scales of <1500 physical kpc. For the first time, we assessed the 2PCF of ̧iv and close to the epoch of reionization utilising the absorber catalogue from the E-XQR-30 survey. We compared this with lower redshift data and find that, on small scales, the clustering of these structures grows with cosmic time. We compared these results to the clustering of galaxies in the GAEA simulations. It appears that the structures traced by ̧iv are broadly comparable to those of the galaxies from the considered simulations. The clustering is most similar to that of the galaxies with virial masses (M) of ∼10 ^ ̊m M _⊙. We do not draw direct comparisons at the smallest separations, to avoid the clustering traced by ̧iv at z∼5 being dominated by contributions from absorbers within a single halo. We require tailor-made simulations to investigate the full range of factors contributing to the observed clustering of the detected metal absorbers. Future ground-based spectrographs will further facilitate surveys of absorbers at this epoch with increased sensitivity.
Welsh et al. (Wed,) studied this question.