Gravitational ringdown signal from coalescences of SMBH binaries - detection rates for LISA and ET

The coalescence history of massive black holes is derived from cosmological simulations, in which their evolution and that of the host galaxies are followed in a consistent way. With the coalescence rate per comoving volume and per mass interval derived from the simulations we estimate the expected detection rate distribution of "ring-down" gravitational wave signals along frequencies accessible by LISA and Einstein Telescope (ET). For LISA, a total detection rate of about 15 yr(-1) is predicted for events having a signal-to-noise ratio equal to 10. For ET, one event each 14 months down to one event each 4 years is expected with a signal-to-noise ratio of 5. The detection of these gravitational signals and their distribution in frequency would be in the future an important tool able to discriminate among different scenarios for the origin of supermassive black holes.