  (abridged) A fundamental subject in Extragalactic Astronomy concerns the
formation and evolution of late-type galaxies (LTGs). The standard scenario
comprises the early assembly of the bulge followed by disk accretion. However,
recent observational evidence points to a joint formation and perpetual
co-evolution of these structural components. Our current knowledge on the
properties of bulge and disk is mostly founded on photometric decomposition
studies, which sensitively depend on the adopted methodology and enclosed
assumptions on the structure of LTGs. A critical assumption whose validity was
never questioned is that galactic disks conserve their exponential nature up to
the galactic center. This implies that bulge and disk co-exist without
significant dynamical interaction and mass exchange over nearly the entire
Hubble time. Our goal is to examine the validity of the standard assumption
that galactic disks preserve their exponential intensity profile inside the
bulge radius all the way to the galactic center. We developed a
spectrophotometric bulge-disk decomposition technique that provides an
estimation for the net spectrum of the bulge. A systematic application of our
spectrophotometric bulge-disk decomposition tool to a representative sample of
135 local LTGs from the CALIFA Survey yields a significant fraction (up to
~30%) of unphysical net-bulge spectra when a purely exponential intensity
profile is assumed for the disk. The obtained results suggest that, for a
significant fraction of LTGs, the disk component shows a down-bending beneath
the bulge. If proven to be true, such result will call for a substantial
revision of structural decomposition studies for LTGs and have far-reaching
implications in our understanding of the photometric properties of their
bulges.
