From population III stars to(super)massive black holes

Pregalatic Massive Black Holes (MBHs) formed within minihalos above the cosmological Jeans mass at z=30, as relics of massive POPIII stars. The merger and accretion history of dark halos and MBHs, followed by means of Montecarlo realizations of the merger hierarchy in a ACDM cosmology, reveals several interesting aspects. A fraction of MBHs accreted gas during major mergers, shining in the EUV/soft X-rays as an early population of miniquasars. Such population could have been responsible of the early reionization of the IGM implied by the recent WMAP data. On the other hand, long dynamical friction timescales in minor mergers left many MBHs wandering in galaxy halos. Finally, one of the most fascinating prediction of the cosmic history of MBHs is the copious emission of low frequency gravitational waves associated to coalescence of MBH binaries, in principle detectable by the planned LISA interferometer.