The environments and hosts of metal absorption at z > 5

Abstract

ABSTRACT A growing population of metal absorbers are observed at z > 5, many showing strong evolution in incidence approaching the epoch of hydrogen reionization. Follow-up surveys examining fields around these metals have resulted in galaxy detections but the direct physical relationship between the detected galaxies and absorbers is unclear. Upcoming observations will illuminate this galaxy–absorber relationship, but the theoretical framework for interpreting these observations is lacking. To inform future z > 5 studies, we define the expected relationship between metals and galaxies using the Technicolor Dawn simulation to model metal absorption from z = 5 to 7, encompassing the end of reionization. We find that metal absorber types and strengths are slightly better associated with their environment than with the traits of their host galaxies, as absorption system strengths are more strongly correlated with the local galaxy overdensity than the stellar mass of their host galaxy. For redshifts prior to the end of the epoch of reionization, strong high-ionization transitions like C iv are more spatially correlated with brighter galaxies on scales of a few hundred proper kpc than are low-ionization systems, due to the former’s preference for environments with higher ultraviolet background amplitudes and those ions’ relative rarity at z > 6. Post-reionization, the galaxy counts near these high-ionization ions are reduced, and increase surrounding certain low-ionization ions due to a combination of their relative abundances and preferred denser gas phase. We conclude that galaxy–absorber relationships are expected to evolve rapidly such that high-ionization absorbers are better tracers of galaxies pre-reionization, while low-ionization absorbers are better post-reionization.