Owing to several observational evidences and theoretical predictions for morphological evolution of galaxies, it is now widely accepted that galaxies do evolve from late types to early ones along the Hubble sequence. It is also well established that non-axisymmetric potentials of bar-like or oval mass distributions can change the morphology of galaxies significantly during the Hubble time. Here, we review the observational and theoretical grounds of the secular evolution driven by bar-like potentials, and present the results of SPH simulations for the response of the gaseous disks to the imposed potentials to explore the secular evolution in the central regions of barred galaxies.

It is now a well established fact that galaxies undergo significant morphological transformation during their lifetimes, manifesting as an evolution along the Hubble sequence from the late to the early Hubble types. The physical processes commonly believed to be responsible for this observed evolution trend, i.e. the major and minor mergers, as well as gas accretion under a barred potential, though demonstrated applicability to selected types of galaxies, on the whole have failed to reproduce the most important statistical and internal properties of galaxies. The secular evolution mechanism reviewed in this paper has the potential to overcome most of the known difficulties of the existing theories to provide a natural and coherent explanation of the properties of present day as well as high-redshift galaxies.

We analyzed the luminosity profiles of 104 bright barred galaxies to examine the frequency of occurrence of the Type II disk which is thought to be the result of redistribution of disk material by bar potential. Our analysis of the elliptically averaged major axis profiles shows that about 70% of the present sample seem to have Type II disks with a weak tendency of preferential occurrence of type II disks in the late type galaxies. there is a subgroup of Type II disks which is characterized by a flat luminosity distribution in the middle disk, followed by a steep decline in the outer parts. Most of the galaxies with strong bars tend to have Type II disks. The present study strongly suggests that Type II disk is an evidence for the secular evolutions in disk galaxies.