Gravitational waves and stalled satellites from massive galaxy mergers at z ≤ 1

Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius

Research output: Contribution to journalArticlepeer-review

67 Scopus citations


We present a model for merger-driven evolution of the mass function for massive galaxies and their central supermassive black holes at late times. We discuss the current observational evidence in favor of merger-driven massive galaxy evolution during this epoch, and demonstrate that the observed evolution of the mass function can be reproduced by evolving an initial mass function under the assumption of negligible star formation. We calculate the stochastic gravitational wave signal from the resulting black hole binary mergers in the low redshift universe (z ≤ 1) implied by this model, and find that this population has a signal-to-noise ratio 2 × to 5 × larger than previous estimates for pulsar timing arrays, with a {2σ, 3σ} lower limit within this model of h c(f = 1 yr-1) = {1.1 × 10 -15, 6.8 × 10-16}. The strength of this signal is sufficient to make it detectable with high probability under conservative assumptions within the next several years. A principle reason that this result is larger than previous estimates is our use of a recent recalibration of the black hole-stellar mass correlation for the brightest cluster galaxies, which increases our estimate by a factor of 2 relative to past results. For cases where a galaxy merger fails to lead to a black hole merger, we estimate the probability for a given number of satellite black holes to remain within a massive host galaxy, and interpret the result in light of ULX observations. We find that in rare cases, wandering supermassive black holes may be bright enough to appear as ULXs.

Original languageEnglish (US)
Article number156
JournalAstrophysical Journal
Issue number2
StatePublished - Jul 10 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • black hole physics
  • galaxies: evolution
  • galaxies: kinematics and dynamics
  • galaxies: luminosity function, mass function
  • gravitational waves
  • pulsars: general


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