| Abstract: The first stars, galaxies, and black holes did more than illuminate the Universe: they transformed it. Their radiation heated and ionized the diffuse hydrogen gas between galaxies, gradually changing the cosmic landscape and making the Universe transparent to ultraviolet light. This transition, from cosmic darkness to a Universe filled with galaxies and radiation, is one of the major frontiers of modern astrophysics. In this talk, I will give an overview of work carried out in my research group at TIFR over the last eight years towards understanding this formative era. I will discuss how theoretical modelling, numerical simulations, and observations of the Lyman-α forest, distant quasars, early galaxies, active galactic nuclei, and the redshifted 21-cm signal can be combined to study the evolving ionization state of the Universe during its first billion years. I will also look ahead to the coming decade, when facilities such as the Square Kilometre Array, the Vera C. Rubin Observatory, JWST, and large spectroscopic surveys will help us move from detecting the first light to understanding how it shaped the cosmos. |
