Galaxy Secular Mass Flow Rate Determination Using the Potential-Density Phase Shift Approach

Abstract

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.