Post-Newtonian Evolution of Massive Black Hole Triplets in Galactic Nuclei: IV. Implications for LISA. (arXiv:1812.01011v1 [astro-ph.GA])

Post-Newtonian Evolution of Massive Black Hole Triplets in Galactic Nuclei: IV. Implications for LISA. (arXiv:1812.01011v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bonetti_M/0/1/0/all/0/1">Matteo Bonetti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sesana_A/0/1/0/all/0/1">Alberto Sesana</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haardt_F/0/1/0/all/0/1">Francesco Haardt</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barausse_E/0/1/0/all/0/1">Enrico Barausse</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Colpi_M/0/1/0/all/0/1">Monica Colpi</a>

Coalescing massive black hole binaries (MBHBs) of $10^{4-7}~rm M_{odot}$,
forming in the aftermath of galaxy mergers, are primary targets of the space
mission LISA, the {it Laser Interferometer Space Antenna}. An assessment of
LISA detection prospects requires an estimate of the abundance and properties
of MBHBs that form and evolve during the assembly of cosmic structures. To this
aim, we employ a semi-analytic model to follow the co-evolution of MBHBs within
their host galaxies. We identify three major evolutionary channels driving the
binaries to coalescence: two standard paths along which the binary evolution is
driven by interactions with the stellar and/or gaseous environment, and a novel
channel where MBHB coalescence occurs during the interaction with a third black
hole. For each channel, we follow the orbital evolution of MBHBs with
physically motivated models that include a self-consistent treatment of the
orbital eccentricity. We find that MBHBs coalesce on timescales that range from
tens of Myrs to several Gyrs, and that LISA will detect between $approx 25$
and $approx 75$ events per year depending on the seed model. We show that
triple-induced coalescences can range from a few detected events up to $sim
30%$ of the total detected mergers. Moreover, even if the standard
gas/stars-driven evolutionary channels should fail and MBHBs were to stall,
triple interactions would still occur as a result of the hierarchical nature of
galaxy formation, resulting in about 10 to 20 LISA detections per year.
Remarkably, triple interactions among the black holes can produce coalescing
binaries with large eccentricities ($gtrsim 0.9$) upon entrance into the LISA
band. This eccentricity will remain significant ($sim 0.1$) also at merger,
requiring suitable templates for parameter estimation.

Coalescing massive black hole binaries (MBHBs) of $10^{4-7}~rm M_{odot}$,
forming in the aftermath of galaxy mergers, are primary targets of the space
mission LISA, the {it Laser Interferometer Space Antenna}. An assessment of
LISA detection prospects requires an estimate of the abundance and properties
of MBHBs that form and evolve during the assembly of cosmic structures. To this
aim, we employ a semi-analytic model to follow the co-evolution of MBHBs within
their host galaxies. We identify three major evolutionary channels driving the
binaries to coalescence: two standard paths along which the binary evolution is
driven by interactions with the stellar and/or gaseous environment, and a novel
channel where MBHB coalescence occurs during the interaction with a third black
hole. For each channel, we follow the orbital evolution of MBHBs with
physically motivated models that include a self-consistent treatment of the
orbital eccentricity. We find that MBHBs coalesce on timescales that range from
tens of Myrs to several Gyrs, and that LISA will detect between $approx 25$
and $approx 75$ events per year depending on the seed model. We show that
triple-induced coalescences can range from a few detected events up to $sim
30%$ of the total detected mergers. Moreover, even if the standard
gas/stars-driven evolutionary channels should fail and MBHBs were to stall,
triple interactions would still occur as a result of the hierarchical nature of
galaxy formation, resulting in about 10 to 20 LISA detections per year.
Remarkably, triple interactions among the black holes can produce coalescing
binaries with large eccentricities ($gtrsim 0.9$) upon entrance into the LISA
band. This eccentricity will remain significant ($sim 0.1$) also at merger,
requiring suitable templates for parameter estimation.

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