Damien Chapon, Lucio Mayer, Romain Teyssier
We study the formation of a supermassive black hole (SMBH) binary and the
shrinking of the separation of the two holes to sub-pc scales starting from a
realistic major merger between two gas-rich spiral galaxies with mass
comparable to our Milky Way. The simulations are the first of this kind carried
out with an Adaptive Mesh refinement (AMR) code (here RAMSES), and the first
capable to resolve separations as small as 0.1 pc. The collision of the two
galaxies produces a gravo-turbulent rotating nuclear disk with mass (\sim 10^9
Msun) and size (\sim 60 pc) in excellent agreement with previous SPH
simulations with particle splitting that used a similar setup (Mayer et al.
2007) but were limited to separations of a few parsecs. The AMR results confirm
that the two black holes sink rapidly as a result of dynamical friction onto
the gaseous background, reaching a separation of 1 pc in less than 10^7 yr. We
show that the dynamical friction wake is well resolved by our model and we find
good agreement with analytical predictions of the drag force as a function of
the Mach number. Below 1 pc, black hole pairing slows down significantly, as
the relative velocity between the sinking SMBH becomes highly subsonic and the
mass contained within their orbit falls below the mass of the binary itself,
rendering dynamical friction ineffective. Non-axisymmetric gas torques do not
arise to restart sinking in absence of efficient dynamical friction, at
variance with previous calculations using idealized equilibrium nuclear disk
models. We believe that the rather "hot" EOS we used to model the multiphase
turbulent ISM in the nuclear region is playing an important role in preventing
efficient SMBH sinking inside the central parsec. We conclude with a discussion
of the way forward to address sinking in gaseous backgrounds at sub-pc scales
approaching the gravitational wave regime.
View original:
http://arxiv.org/abs/1110.6086
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