The observations of high redshift quasars up to z~7 tell us that massive black holes (MBHs) were already in place, with masses well above 10^9 solar masses, when the Universe was less than 1 Gyr old. According to the currently accepted framework, MBHs gain most of their mass via radiatively efficient accretion, hence we expect they formed early in the Universe as smaller seeds. Explaining how these MBHs formed and rapidly grew is particularly challenging, in particular when we also consider that these MBHs seem overmassive compared to the local population. After highlighting the main formation mechanisms proposed to date, I will discuss whether the peculiar environmental conditions in which these systems form and evolve can lead to the formation of massive seeds, and which processes can inhibit this formation mechanism. I will then discuss the subsequent evolution of these protogalaxies and their central MBHs up to the observed masses, the interaction between the MBH and its galaxy host, and the impact of different observational tracers on the apparent obesity of MBHs.
Finally, I will introduce a new state-of-the-art model aimed at addressing the formation and early evolution of the first seed BHs, which is able to directly follow stars and BHs at a few tens of Msun resolution, including stellar feedback, BH accretion and feedback, and an accurate treatment of BH dynamics.
Raffaella Schneider, Luca Graziani