AGN Activity in Nucleated Galaxies as Measured by Chandra
  Motivated by theoretical expectations that Nuclear Star Clusters (NSCs) in
galactic centers may provide a favorable environment for super-massive black
holes to form and/or efficiently grow, we set out to measure the fraction of
nearby nucleated galaxies that also host an Active Galactic Nucleus (AGN). We
targeted a distance-limited sample of 98 objects with the Chandra X-ray
Telescope, down to a uniform X-ray luminosity threshold of $\sim$10$^{38}$ erg
s$^{-1}$. The sample is composed of 47 late-types and 51 early-types, enabling
us to further investigate the active fraction as a function of galactic
morphology. After correcting for contamination to the nuclear X-ray signal from
bright X-ray binaries, we measure an active fraction $f$=11.2$\%^{+7.4}_{-4.9}$
(1$\sigma$ C.L.) across the whole sample, in agreement with previous estimates
based on an heterogeneous combination of optical, X-ray and radio diagnostics,
by Seth et al. (2008). After accounting for the different stellar mass
distributions in our samples, we find no statistically significant difference
in the active fraction of early- vs. late-type nucleated galaxies, with
$f$=10.6$\%^{+11.9}_{-4.9}$ and 10.8$\%^{+11.3}_{-6.3}$, respectively. For the
early-type nucleated galaxies, we are able to carry out a controlled comparison
with a parent sample of non-nucleated galaxies covering the same stellar mass
range, finding again no statistically significant difference in the active
fraction. Taken at face value, our findings suggest that the presence of a NSC
does not facilitate nor enhance accretion-powered emission from a nuclear
super-massive black hole. This is true even for late-type nucleated galaxies,
home to bluer NSCs and arguably larger gas reservoirs.
