No evidence for small disk-like bulges in a sample of late-type spirals
  About 20% of low-redshift galaxies are late-type spirals with a small or no
bulge component. Although they are the simplest disk galaxies in terms of
structure and dynamics, the role of the different physical processes driving
their formation and evolution is not yet fully understood. We investigated
whether small bulges of late-type spirals follow the same scaling relations
traced by ellipticals and large bulges and if they are disk-like or classical
bulges. We derived the photometric and kinematic properties of 9 nearby
late-type spirals. To this aim, we analyzed the surface brightness distribution
from the i-band images of the Sloan Digital Sky Survey and obtained the
structural parameters of the galaxies from a two-dimensional photometric
decomposition. We measured the line-of-sight stellar velocity distribution
within the bulge effective radius from the long-slit spectra taken with high
spectral resolution at the Telescopio Nazionale Galileo. We used the
photometric and kinematic properties of the sample bulges to study their
location in the Fundamental Plane, Kormendy, and Faber-Jackson relations
defined for ellipticals and large bulges. We found that our sample bulges
satisfy some of the photometric and kinematic prescriptions for being
considered disk-like bulges such as small sizes and masses with nearly
exponential light profiles, small bulge-to-total luminosity ratios, low stellar
velocity dispersions, and ongoing star formation. However, each of them follows
the same scaling relations of ellipticals, massive bulges, and compact
early-type galaxies so they cannot be classified as disk-like systems. We find
a single population of galaxy spheroids that follow the same scaling relations,
where the mass seems to lead to a smooth transition in the photometric and
kinematic properties from less massive bulges to more massive bulges and
ellipticals.
