The Cosmic Dawn and Epoch of Reionisation with SKA

Abstract

Concerted effort is currently ongoing to open up the Epoch of Reionization\n(EoR) ($z\\sim$15-6) for studies with IR and radio telescopes. Whereas IR\ndetections have been made of sources (Lyman-$\\alpha$ emitters, quasars and\ndrop-outs) in this redshift regime in relatively small fields of view, no\ndirect detection of neutral hydrogen, via the redshifted 21-cm line, has yet\nbeen established. Such a direct detection is expected in the coming years, with\nongoing surveys, and could open up the entire universe from $z\\sim$6-200 for\nastrophysical and cosmological studies, opening not only the EoR, but also its\npreceding Cosmic Dawn ($z\\sim$30-15) and possibly even the later phases of the\nDark Ages ($z\\sim$200-30). All currently ongoing experiments attempt\nstatistical detections of the 21-cm signal during the EoR, with limited\nsignal-to-noise. Direct imaging, except maybe on the largest (degree) scales at\nlower redshifts, as well as higher redshifts will remain out of reach. The\nSquare Kilometre Array(SKA) will revolutionize the field, allowing direct\nimaging of neutral hydrogen from scales of arc-minutes to degrees over most of\nthe redshift range $z\\sim$6-28 with SKA1-LOW, and possibly even higher\nredshifts with the SKA2-LOW. In this SKA will be unique, and in parallel\nprovide enormous potential of synergy with other upcoming facilities (e.g.\nJWST). In this chapter we summarize the physics of 21-cm emission, the\ndifferent phases the universe is thought to go through, and the observables\nthat the SKA can probe, referring where needed to detailed chapters in this\nvolume (Abridged).\n