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Understanding how chemical elements are distributed in time and space across the universe is a major question in Astrophysics, and one of the key goals of the ARC Centre of Excellence ASTRO 3D. I’ll summarise my team’s recent efforts in tracing the elements in the early universe using ESO/VLT via the XQR-30 survey of intervening metal absorbers towards z~6 quasars. With the benefit of the long lever arm from z=1.9 to 6.4, high sensitivity, resolution and significant number statistics, we can make inroads. Strong MgII absorbers trace the global star formation rate density, in contrast to the incidence of weak MgII in the Circumgalactic Medium (CGM) that remains remarkably flat across cosmic time. Metals ions trace both chemical enrichment and the ionization state of the CGM. I’ll show how a decline in CIV, coupled with a rise in CII and OI complements current evidence for a late reionization continuing to occur in metal-enriched and therefore biased regions of the Universe. Finally, in direct comparison with JWST, I will demonstrate why medium resolution ground-based spectroscopy is essential for a complete census of the high z CGM. |
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