  Binary black holes (BBHs) are one of the endpoints of isolated binary
evolution, and their mergers a leading channel for gravitational wave events.
Here, using the evolutionary code \textsc{StarTrack}, we study the statistical
properties of the BBH population from isolated binary evolution for a range of
progenitor star metallicities and BH natal kicks. We compute the mass function
and the distribution of the primary BH spin $a$ as a result of mass accretion
during the binary evolution, and find that this is not an efficient process to
spin up BHs, producing an increase by at most $a\sim$~0.2--0.3 for very low
natal BH spins. We further compute the distribution of merger sites within the
host galaxy, after tracking the motion of the binaries in the potentials of a
massive spiral, a massive elliptical, and a dwarf galaxy. We find that a
fraction of 70-90\% of mergers in massive galaxies and of 40-60\% in dwarfs
(range mostly sensitive to the natal kicks) is expected to occur inside of
their hosts.
  The number density distribution at the merger sites further allows us to
estimate the broadband luminosity distribution that BBH mergers would produce,
\textit{if} associated with a kinetic energy release in an outflow, {which, as
a reference, we assume at the level inferred for the \textit{Fermi} GBM
counterpart to GW150914, with the understanding that current limits from the O1
and O2 runs would require such emission to be produced within a jet of angular
size within $\lesssim 50^\circ$.}
