The atomic Hydrogen content of the post-reionization Universe

In this talk I will present a comprehensive analysis of atomic hydrogen (HI) properties using a semi-analytical model of galaxy formation and N-body simulations covering a large cosmological volume at high resolution. I will examine the HI mass function and the HI density, characterizing both their redshift evolution and their dependence on hosting halo mass. I will discuss the HI content of dark matter haloes in the local Universe and up to redshift z=5, analyzing the contribution of different galaxy properties. I will present results on HI clustering relevant for future 21cm Intensity Mapping (IM) experiments, including the HI bias and the shot noise level. I will detail the contribution from various galaxy properties on the HI power spectrum and their relation to the halo bias. Finally, I will present the 21cm signal in redshift space, a fundamental prediction to be tested against data from future radio telescopes such as SKA.