Revisiting the role of bars in AGN fuelling with propensity score sample
  matching
  The high luminosity displayed by an active galactic nucleus (AGN) requires
that gas be transported to the centre of the galaxy by some mechanism.
Bar-driven processes are often pointed out in this context and a number of
studies have addressed the bar-AGN connection, but with conflicting results.
Some of the inconsistencies can be explained by the different spatial- and
timescales involved in bar-driven gas inflows, accretion by the central black
hole, and AGN emission. However, the discrepant results could also be due to
sample biases, because both the AGN activity determination and the bar
detection are influenced by the method employed. We revisit the bar-AGN
connection in a sample of galaxies from SDSS, looking for evidence of the
influence of bars on AGN activity. We determine AGN activity by emission line
diagnostics and the properties of the bar were previously estimated with
\texttt{BUDDA}, which performs 2D bulge-bar-disk decomposition. Before
comparing active and inactive galaxies, we made a careful selection of the
sample to minimise selection biases. We created control samples by matching
them with the AGN sample using propensity score matching. This technique offers
an analytical approach for creating control samples given some object
parameters. We find that AGN are preferentially found in barred galaxies and
that the accretion rate is higher in barred galaxies, but only when different
M-$\sigma$ relations are used to estimate the black hole mass M$_\bullet$ in
barred and unbarred galaxies (from the central velocity dispersion $\sigma$).
On the other hand, we find no correlation between activity level and bar
strength. Altogether, our results strengthen theoretical predictions that the
bar is an important mechanism in disc galaxies, creating a gas reservoir to
feed AGN, but they also indicate that other mechanisms can play a major role,
particularly at scales <~100 pc.
