Galaxy Secular Mass Flow Rate Determination Using the Potential-Density
  Phase Shift Approach: Application to Six Nearby Spiral Galaxies
  Using the potential-density phase shift approach developed by the present
authors in earlier publications, we estimate the magnitude of radial mass
accretion/excretion rates across the disks of six nearby spiral galaxies having
a range of Hubble types. Our goal is to examine these rates in the context of
bulge building and secular morphological evolution along the Hubble sequence.
Stellar surface density maps of the sample galaxies are derived from SINGS
3.6um and SDSS i-band images. Corresponding molecular and atomic gas surface
densities are derived from published CO(1-0) and HI interferometric
observations of the BIMA SONG, THINGS, and VIVA surveys. The mass flow rate
calculations utilize a volume-type torque integral to calculate the angular
momentum exchange rate between the basic state disk matter and density wave
modes. The potential-density phase shift approach yields angular momentum
transport rates several times higher than those estimated using the Lynden-Bell
and Kalnajs (1972) approach. The current approach leads to predictions of
significant mass redistribution induced by the quasi-steady density wave modes,
enough for the morphological types of disks to evolve substantially within its
lifetime. This difference with the earlier conclusions of Lynden-Bell and
Kalnajs reflects the dominant role played by collisionless shocks in the
secular evolution of galaxies containing extremely non-linear, quasi-steady
density wave modes, thus enabling significant morphological transformation
along the Hubble sequence during a Hubble time. We show for the first time
also, 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, with the latter being
what had been emphasized in most of the previous secular evolution studies.
