Detection of a Distinct Pseudobulge Hidden Inside the "Box-Shaped Bulge"
  of NGC 4565
  N-body simulations show that "box-shaped bulges" of edge-on galaxies are not
bulges at all: they are bars seen side-on. The two components that we readily
see in edge-on Sb galaxies like NGC 4565 are a disk and a bar, but face-on SBb
galaxies always show a disk, a bar, and a (pseudo)bulge. Where is the
(pseudo)bulge in NGC 4565? We use archival Hubble Space Telescope K-band and
Spitzer Space Telescope 3.6 um images to penetrate the dust in NGC 4565. We
find a high surface brightness, central stellar component, distinct from the
boxy bar and from the galaxy's disk. Its minor-axis profile has a Sersic index
of 1.33+/-0.12, so it is a pseudobulge. The pseudobulge has the smallest scale
height (~90 pc) of any component in the galaxy, in contrast to ~740 pc for the
boxy bar plus thin disk. The disky pseudobulge is also much less luminous than
the boxy bar, so the true (pseudo)bulge-to-total luminosity ratio of the galaxy
is much less than previously thought. We infer that the pseudobulge-to-total
luminosity ratios of edge-on galaxies with box-shaped bulges have generally
been overestimated. Therefore more galaxies than we have recognized contain
little or no evidence of a merger-built classical bulge. This challenges our
picture of galaxy formation by hierarchical clustering, because it is difficult
to grow big galaxies without also making a big classical bulge. Solving the
puzzle of the "missing pseudobulge" in NGC 4565 further increases our
confidence that we understand box-shaped bulges correctly as edge-on bars. This
supports our developing picture of the formation of pseudobulges -- both
edge-on bars and disky central components -- by secular evolution in isolated
galaxies.
