PROFESSOR AVINASH DESHPANDE

A number of on-going and planned future efforts at low radio frequencies aim to detect precious tokens of the yet unobserved details of the transition from the dark ages to the cosmic dawn and beyond to completion of reionization, heralded by the first stars. The potential detectability of global signal from the red-shifted 21-cm line of atomic hydrogen across this cosmic transition was first discussed by Shaver et al. (1999). Detection of such signals holds unmatched promise to reveal several key details of the physical condition and constituents of the universe during these early epochs. However, the associated challenges are not confined only to isolating the weak signal of interest from the orders of magnitude brighter foregrounds, but extend equally to reliably establishing the origin of the apparent global signal to the very early epochs. The talk will highlight the challenges in such measurements and the attempts so far to detect the global signal, including the recently claimed “detection of a flattened absorption profile in the sky-averaged radio spectrum” by Bowman et al (2018). The potential of a novel model-independent path toward isolating the foreground contribution will be discussed, and a critical dipole test that the measurements of the global cosmic-dawn signal should necessarily pass will be presented.