Testing Models of Supermassive Black Hole Seed Formation through Gravity Waves

We study the gravitational wave background produced from the formation andassembly of supermassive black holes within the cosmological paradigm ofhierarchical structure formation. In particular, we focus on a supermassiveblack hole formation scenario in which the present-day population ofsupermassive black holes is built from high-mass seed black holes and wecompute the concomitant spectrum of gravitational radiation produced by mergersof the seed black holes. We find that this scenario predicts a large,gravitational wave background that should be resolved into individual sourceswith space interferometers such as the proposed Laser Interferometric SpaceAntenna (LISA). The number of inspiral, merger and ringdown events above asignal to noise ratio of 5 that result from massive black hole seeds is oforder 10^3. This prediction is robust and insensitive to several of the detailsof the model. We conclude that an interferometer such as LISA will be able toeffectively rule out or confirm a class of models where supermassive blackholes grow from high-mass seed black holes and may be able to place stronglimits on the role of mergers as a channel for supermassive black hole growth.Supermassive black hole seeds likely form in the earliest proto-galacticstructures at high redshift and the masses of supermassive black holes areknown to be strongly correlated with the potentials of the spheroids in whichthey reside, therefore these results imply that space interferometers can beused as a powerful probe of the physics of galaxy formation and proto-galaxyformation at very high redshift.Comment: Replaced to match version accepted for publication in the Astrophysical Journa