Prof. Emma Ryan-Weber

"Probing Reionization with high-z metals"
Understanding how chemical elements are distributed in time and space across the universe provides key observational markers for the first stars. I'll summarise my team's recent efforts in tracing elements in the early universe using ESO/VLT/X-shooter via the EXQR-30 survey of intervening metal absorbers towards 42 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 have made meaningful inroads. Metal ions trace both chemical enrichment and the ionization state of the Circumgalactic Medium (CGM). We find that the ionization of the CGM differs significantly over the short period of cosmic time from redshift 5.5 to 6. I'll show how a decline in the incidence of intervening CIV absorbers, 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. A flat evolution in weak MgII is also found, despite a decline in cosmic metal content. 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.