Gravitational Radiation From Super-Massive Black-Hole Binaries

摘要

Recent observational evidence ties the mass of supermassive black-holes to the circular velocities of their host dark-matter halos, and suggests that this relation is independent of redshift. We show that a simple model including the combination of the black-hole - circular velocity relation with the dark matter halo mass function and merger rate reproduces the details of the optical and X-ray quasar luminosity functions at high redshift within a standard Lambda-CDM cosmology. A similar approach can be used to estimate the expected rate of gravitational wave emission from merging super-massive black-holes. These calculations suggest an event rate for the LISA satellite that may be as high as one hundred per year unless most super-massive black-hole binaries have hardening timescales longer than a Hubble time. We discuss the effect of reionization on the redshift distribution of gravitational wave sources and show that most sources for LISA may come from z>6. Finally we find that the nHz frequency back-ground is dominated by black-hole binaries at z<2, and that pulsar timing experiments are already nearing the level where limits may be placed on the fraction of black-hole binaries that achieve coalescence.