The effect of AGN feedback on the migration timescale of supermassive
  black holes binaries
  The gravitational interaction at parsec to sub-parsec scales between a
circumbinary gas disc and a super massive black hole binary (SMBHB) is a
promising mechanism to drive the migration of SMBHBs toward coalescence. The
typical dynamical evolution can be separated in two main regimes: I) Slow
migration ($T_{\rm mig}$ $\sim$ $10^{3-4}\times T_{\rm orb}$), where viscous
torques are not efficient enough to redistribute the extracted angular momentum
from the binary, leading to the formation of a low density cavity around the
binary. II) Fast migration ($T_{\rm mig}$ $\sim$ $10^{1-2} \times T_{\rm
orb}$), in which the redistribution of angular momentum is efficient and no low
density cavity is formed in the circumbinary disc. Using N-Body/SPH simulations
we study the effect of AGN feedback in this phase of a SMBHB evolution. We
implement an AGN feedback model in the SPH code Gadget-3 that includes momentum
feedback from winds, X-ray heating/radial-momentum and Eddington force. Using
this implementation we run a set of simulations of SMBHB+disc in the two main
shrinking regimes. From these simulations we conclude that the effect of the
AGN mechanical feedback is negligible for SMBHBs in the slowly shrinking
regime. However, in the fast shrinking regime the AGN wind excavate a "feedback
cavity" leaving the SMBHB almost naked, thus stalling the orbital decay of the
binary.
