We revisit the predictions for the merger rate of massive black hole binaries detectable by the Laser Interferometer Space Antenna ( LISA ) and their background signal for pulsar-timing arrays .
We focus on the effect of the delays between the merger of galaxies and the final coalescence of black hole binaries , and on the effect of supernova feedback on the growth of black holes .
By utilizing a semi-analytic galaxy formation model , not only do we account for the processes that drive the evolution of binaries at separations \lesssim 1 pc ( gas-driven migration , stellar hardening and triple/quadruple massive black hole systems ) , but we also improve on previous studies by accounting for the time spent by massive black hole pairs from kpc down to a few pc separation .
We also include the effect of supernova feedback , which may eject a substantial amount of gas from the nuclear region of low-mass galaxies , thus hampering the growth of black holes via accretion and suppressing their orbital migration in circumbinary disks .
In spite of the inclusion of these novel physical effects , we predict that the LISA detection rate should still be in excess of \sim 2 \mbox { yr } ^ { -1 } , irrespective of the model for the seeds of the black hole population at high redshifts .
However , scenarios in which black holes form from \sim 100 M _ { \odot } seeds are more significantly impacted by the feedback from supernovae .
We also present predictions for the mass ratio distribution of the merger population , and find that binaries typically have mass ratios between \sim 0.1 and 1 .
Predictions for the stochastic background in the band of pulsar-timing array experiments are instead rather robust , and show only a mild dependence on the model .