Cospatial 21 cm and metal-line absorbers in the epoch of reionization – I. Incidence and observability

ABSTRACTf Overdense, metal-rich regions, shielded from stellar radiation might remain neutral throughout reionization and produce metal as well 21 cm absorption lines. Simultaneous metals can complement each other probes of underlying gas properties. We use Aurora, a suite high-resolution radiation-hydrodynamical simulations galaxy formation, to investigate the occurrence such ‘aligned’ absorbers. calculate spectra for cm, O I, C II, Si Fe II. find velocity windows with at least one classify aligned absorbers into two categories: ‘aligned cospatial absorbers’ but not absorbers’. While originate overdense structures be used trace properties, are due peculiar effects. The incidence is redshift dependent, it dictated by interplay between enrichment, shows peak z ≈ 8 disappear towards end because lack an ambient forest, associated pockets that found lower redshift. mock observations set sightlines next generation telescopes like ELT SKA1-LOW, finding given sufficiently bright background quasar, these will able detect both types reionization.