Supermassive black holes and their host spheroids I. Disassembling
  galaxies
  Several recent studies have performed galaxy decompositions to investigate
correlations between the black hole mass and various properties of the host
spheroid, but they have not converged on the same conclusions. This is because
their models for the same galaxy were often significantly different and not
consistent with each other in terms of fitted components. Using $3.6 \rm ~\mu
m$ $Spitzer$ imagery, which is a superb tracer of the stellar mass (superior to
the $K$-band), we have performed state-of-the-art multicomponent decompositions
for 66 galaxies with directly measured black hole masses. Our sample is the
largest to date and, unlike previous studies, contains a large number (17) of
spiral galaxies with low black hole masses. We paid careful attention to the
image mosaicking, sky subtraction and masking of contaminating sources. After a
scrupulous inspection of the galaxy photometry (through isophotal analysis and
unsharp masking) and - for the first time - 2D kinematics, we were able to
account for spheroids, large-scale, intermediate-scale and nuclear disks, bars,
rings, spiral arms, halos, extended or unresolved nuclear sources and partially
depleted cores. For each individual galaxy, we compared our best-fit model with
previous studies, explained the discrepancies and identified the optimal
decomposition. Moreover, we have independently performed 1D and 2D
decompositions, and concluded that, at least when modelling large, nearby
galaxies, 1D techniques have more advantages than 2D techniques. Finally, we
developed a prescription to estimate the uncertainties on the 1D best-fit
parameters for the 66 spheroids that takes into account systematic errors,
unlike popular 2D codes that only consider statistical errors.
