Quantifying the Coexistence of Massive Black Holes and Dense Nuclear
  Star Clusters
  In large spheroidal stellar systems, such as elliptical galaxies, one
invariably finds a 10^6-10^9 M_Sun supermassive black hole at their centre. In
contrast, within dwarf elliptical galaxies one predominantly observes a
10^5-10^7 M_Sun nuclear star cluster. To date, few galaxies have been found
with both type of nuclei coexisting and even less have had the masses
determined for both central components. Here we identify one dozen galaxies
housing nuclear star clusters and supermassive black holes whose masses have
been measured. This doubles the known number of such hermaphrodite nuclei -
which are expected to be fruitful sources of gravitational radiation. Over the
host spheroid (stellar) mass range from 10^8 to 10^11 M_Sun, we find that a
galaxy's nucleus-to-spheroid (baryon) mass ratio is not a constant value but
decreases from a few percent to ~0.3 percent such that log[(M_BH+M_NC)/M_sph] =
-(0.39+/-0.07)log[M_sph/10^10 M_Sun] -(2.18+/-0.07). Once dry merging has
commenced by M_sph ~ 10^11 M_Sun and the nuclear star clusters have
disappeared, this ratio is expected to become a constant value.
  As a byproduct of our investigation, we have found that the projected flux
from resolved nuclear star clusters can be well approximated with Sersic
functions having a range of indices from ~0.5 to ~3, the latter index
describing the Milky Way's nuclear star cluster.
