Intrinsic and observed dual AGN fractions from major mergers
  A suite of 432 collisionless simulations of bound pairs of spiral galaxies
with mass ratios 1:1 and 3:1, and global properties consistent with the
$\Lambda$CDM paradigm, is used to test the conjecture that major mergers fuel
the dual AGN (DAGN) of the local volume. Our analysis is based on the premise
that the essential aspects of this scenario can be captured by replacing the
physics of the central BH with restrictions on their relative separation in
phase space. We introduce several estimates of the DAGN fraction and infer
predictions for the activity levels and resolution limits usually involved in
surveys of these systems, assessing their dependence on the parameters
controlling the length of both mergers and nuclear activity. Given a set of
constraints, we find that the values adopted for some of the latter factors
often condition the outcomes from individual experiments. Still, the results do
not reveal, in general, very tight correlations, being the tendency of the
frequencies normalized to the merger time to anticorrelate with the orbital
circularity the clearest effect. In agreement with other theoretical studies,
our simulations predict intrinsic abundances of these systems that range from
$\sim$few to $15\%$ depending on the maximum level of nuclear activity
achieved. At the same time, we show that these probabilities are reduced by
about an order of magnitude when they are filtered with the typical constraints
applied by observational studies of the DAGN fraction at low redshift. As a
whole, the results of the present work prove that the consideration of the most
common limitations involved in the detection of close active pairs at optical
wavelengths is sufficient by itself to reconcile the intrinsic frequencies
envisaged in a hierarchical universe with the small fractions of double-peaked
narrow-line systems which are often reported at kpc-scales.
