Gravitational Wave Background from Supermassive Black Holes

Cosmological simulations were performed in which the growth of 100 M⊙ black hole seeds as well as the evolution of the host galaxy were followed in a self-consistent way. Seeds grow mainly by accretion of baryonic matter and by coalescences occurring after merger events. The gravitational wave background resulting from these coalescences (essentially the ring-down emission) was estimated from the black hole coalescence rate per mass interval as a function of the redshift, which was estimated for the first time based on t he present cosmological simulations. Our results indicate that such a background is a "shot-noise" like with frequencies covering a range from 10 −6 Hz up to mHz, a region sensitive by LISA. Such a kind of background allows one to individually detect the ringing-down SMBHs. We then estimate the expected detection rate for LISA.