The abundances and properties of Dual AGN and their host galaxies in the
  EAGLE simulations
  We look into the abundance of Dual AGN in the largest hydrodynamical
simulation from the EAGLE project. We define a Dual AGN as two active black
holes (BHs) with a separation below 30 kpc. We find that only 1 per cent of AGN
with $\LhX\geq 10^{42}\ergs$ are part of a Dual AGN system at $z=0.8-1$. During
the evolution of a typical binary BH system, the rapid variability of the hard
X-ray luminosity on Myr time-scales severely limits the detectability of Dual
AGN. To quantify this effect, we calculate a probability of detection, $t_{\rm
on}/t_{\rm 30}$, where $t_{\rm 30}$ is the time in which the two black holes
are separated at distances below 30 kpc and $t_{\rm on}$, the time that both
AGN are visible (e.g. when both AGN have $\LhX\geq 10^{42}\ergs$) in this
period. We find that the average fraction of visible Dual systems is 3 per
cent. The visible Dual AGN distribution as a function of BH separation presents
a pronounced peak at $\sim 20$ kpc that can be understood as a result of the
rapid orbital decay of the host galaxies after their first encounter. We also
find that $75$ per cent of the host galaxies have recently undergone or are
undergoing a merger with stellar mass ratio $\geq 0.1$. Finally, we find that
the fraction of visible Dual AGN increases with redshift as found in
observations.
