**Authors**: Sean T. McWilliams, Jeremiah P. Ostriker, Frans Pretorius

**Date**: 22 Nov 2012

**Abstract**: 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 as much as ~5x larger than previous estimates for pulsar timing arrays, with an expectation value for the characteristic strain h_c(f =1 yrˆ{-1})=5.8 x 10ˆ{-15} that is already in tension with observational constraints, and a 2-sigma lower limit within this model of h_c(f =1 yrˆ{-1})=2.0 x 10ˆ{-15}. The strength of this signal may therefore be detectable with the data already collected using the current generation of pulsar timing arrays, and could be detected with high statistical significance under conservative assumptions within the next few years, if the principle assumption of merger-driven galaxy evolution since z=1 holds true. For cases where a galaxy merger fails to lead to a black hole merger, we estimate the probability for a given number of satellite unmerged black holes to remain within a massive host galaxy, and interpret the result in light of ULX observations. In particular, we find that the brightest cluster galaxies should have 1-2 such sources with luminosities above 10ˆ{39} erg/s, which is consistent with the statistics of observed ULXs.

1211.5377
(/preprints)

2012-11-27, 18:53
**[edit]**

© M. Vallisneri 2012 — last modified on 2010/01/29

*Tantum in modicis, quantum in maximis*