APEC Seminar (Astronomy - Particle Physics - Experimental Physics - Cosmology)

Speaker: Girish Kulkarni (TIFR )
Title: When did cosmic reionization happen?
Date: Thu, Sep 26, 2019, 13:30 - 14:30
Place: Seminar Room A
Abstract: Cosmic reionization is the last global phase transition of the Universe. As such, when reionization happened and what caused it have been two of the most important questions in cosmology in the last two decades. Unfortunately, progress on these questions has been slow, due in part to difficulties such as lack of bright high-redshift quasars, the large cross section of the Lyman-alpha transition, and the near impossibility of measuring the Lyman-continuum escape fraction of high-redshift galaxies. In this talk I will discuss how this situation has now changed thanks to the unexpected measurement of large spatial variations in the Lyman-alpha forest at redshift 5.5 and its rather surprising theoretical interpretation. I will argue that we now see a remarkable concordance in a variety of high-redshift data, which makes us more confident than before about when cosmic reionization ended. I will also discuss where we intend to go from here by exploiting radio and infrared intensity mapping on the one hand and high-resolution near-infrared spectroscopy of high-redshift quasars on the other.