  We have carried out an initial study of a small sample of nearby spiral and
barred galaxies with a broad distribution of Hubble types in order to have a
first estimate of the magnitude of their secular mass accretion/excretion rates
in the context of bulge building and morphological evolution along the Hubble
sequence. The stellar surface density maps of the sample galaxies were derived
from the archival data of SINGS and SDSS. The corresponding molecular and
atomic surface densities were derived from archival CO(1-0) and HI
interferometric observations of the BIMA SONG, THINGS, and VIVA surveys. The
method used for determining the radial mass flow rates follows from our
previous work using the potential-density phase shift approach, which utilizes
a volume-type torque integral to calculate the angular momentum exchange rate
between the basic state disk matter and the density wave modes. This approach
yields radial mass flow rates and angular momentum transport rates several
times higher than similar rates estimated using the traditional method of
gravitational torque couple of Lynden-Bell and Kalnajs 1972, and this
difference reflects the dominant role played by collisionless shocks in the
secular evolution of galaxies containing extremely non-linear, quasi-steady
density wave modes. It is shown that these non-linear modes maintains their
quasi-steady state at the expense of a continuous radial mass flow and the
resulting morphological transformation of galaxies throughout their lifetime,
not only for late-type and intermediate-type disk galaxies but, under favorable
conditions, also for earlier types including S0s and disky ellipticals. We show
here for the first time using observational data that stellar mass
accretion/excretion is just as important, and oftentimes much more important,
than the corresponding accretion/excretion processes in the gaseous component.
