S21B0003

Determining when and how the Universe made a phase transition from neutral to almost completely ionised remains a paramount goal of modern astrophysics. Powerful high redshift radio sources are unique beacons against which absorption by the neutral gas that pervaded the very early Universe can be seen in the HI 21cm line. 21 cm absorption studies with LOFAR and SKA are powerful tools to constrain reionisation on the important kpc scales. However, no bright radio sources against which 21cm absorption could be measured are currently known at z≥6. New all-sky radio surveys with LOFAR are in principle capable of detecting hundreds of radio-loud sources in the EoR, and here we propose to observe 18 of the most promising radio loud quasars at z≥6. These candidates have been selected using the unique combination of LOFAR with DESI Legacy Surveys and WISE, and are bright at radio wavelengths. We request 2 nights using Subaru/FOCAS to spectroscopically confirm these z≥6 quasar candidates using the Lyα emission line. Increasing the number of confirmed radio-loud quasars at z≥6 is essential to study how reionisation unfolded globally, through 21cm absorption across multiple lines of sight using current and future radio telescopes.

This document was translated from L^AT_EX by H^EV^EA.