Probing the Epoch of Reionization with Low Frequency Arrays

Abstract. The Epoch of Reionization (EoR) is the epoch in which hydrogen in the Universe reionize after the “Dark Ages”. This is the second of two major phase transitions that hydrogen in the Universe underwent, the first phase being the recombination era in which hydrogen became neutral at redshift ≈ 1100. The EoR, occurs around z ≈ 10 and is probably caused by the first radiation emitting astrophysical sources, hence it is crucial to our understanding of when and how the Universe “decided ” to start forming astrophysical objects and how that influenced subsequent structure formation in the Universe. As such, the EoR is related to many fundamental questions in cosmology, galaxy formation, quasars and very metal poor stars; all are foremost research issues in modern astrophysics. The redshifted 21 cm hyperfine line is widely considered as the most promising probe for studying the EoR in detail. In the near future a number of low frequency radio telescopes (LOFAR, MWA, GMRT and SKA) will be able to observe the 21 cm radiation arriving from the high redshift Universe. In this paper I present our current picture of the ionization process, review the 21 cm line physics and discuss the challenges that the current generation experiments are expected to face. Finally, I discuss the potential of SKA in exploring the EoR and the Universe’s Dark Ages. 1