TAPIR Seminar

The baryons in the post-reionization (z < 6) universe reside chiefly in the partially (re)ionized, low density intergalactic medium (IGM), with a small fraction in the neutral, high column density systems such as galaxies and Damped Lyman Alpha absorbers (DLAs). The thermal evolution of the IGM offers valuable insights into the epochs of hydrogen and helium reionization in the universe. I will describe our work towards constraining the temperature-density relation of the IGM by using the Lyman-alpha forest of hydrogen absorption lines in the spectra of distant quasars, and the implications for reionization. In the post-reionization universe, the high column density neutral hydrogen (HI) is preferentially probed either through 21-cm emission surveys/intensity mapping experiments, or Damped Lyman Alpha (DLA) absorption observations. There exist different analytical prescriptions in the literature for modelling the 21-cm and DLA observations of the post-reionization HI. I will describe the reconciliation of these two differing approaches towards a consistent model of the distribution and evolution of HI across z ~ 0 - 4. The model has implications for the characteristic host halo masses of the DLAs and the power spectrum of 21-cm intensity fluctuations.