Detection of a Pseudobulge Hidden Inside the "Box-Shaped Bulge" of NGC
  4565
  Numerical simulations show that box-shaped bulges of edge-on galaxies are not
bulges: they are bars seen side-on. Therefore the two components that are seen
in edge-on Sb galaxies such as 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 H-band images
and Spitzer Space Telescope 3.6 micron wavelength images, both calibrated to
2MASS K_s band, to penetrate the prominent dust lane in NGC 4565. We find a
high surface brightness, central stellar component that is clearly distinct
from the boxy bar and from the disk. Its brightness profile is a Sersic
function with index n = 1.55 +- 0.07 along the major axis and 1.33 +- 0.12
along the minor axis. Therefore it is a pseudobulge. It is much less luminous
than the boxy bar, so the true pseudobulge-to-total luminosity ratio of the
galaxy is PB/T = 0.06 +- 0.01, much less than the previously believed value of
B/T = 0.4 for the boxy bulge. We infer that published B/T luminosity ratios of
edge-on galaxies with boxy bulges have been overestimated. Therefore, more
galaxies than we thought contain little or no evidence of a merger-built
classical bulge. From a formation point of view, NGC 4565 is a giant, pure-disk
galaxy. This presents a challenge to our picture of galaxy formation by
hierarchical clustering: it is difficult to grow galaxies as big as NGC 4565
without also making big classical bulges.
