Color Gradients and the Secular Evolutionary Scenario in Late-Type Spiral Galaxies

Abstract

We have done a robust statistical study of the behaviour of color profiles for 257 Sbc galaxies, having determined (B-V) and (U-B) color gradients, as well as color indices of bulges and disks separately. Applying a bidimensional decomposition technique to model the brightness profiles of bulges and disks, we obtained characteristic structural parameters for 39 galaxies. Among the main results obtained, we point out: 65% of the galaxies have negative color gradients (reddish inward), 25% have no gradients, and 10% show positive gradients; galaxies that show no color gradients tend to be barred; we confirm the correlation between the color indices of bulges and disks; the absence of correlation between color and metallicity gradients suggests that the excess of barred galaxies with zero or positive color gradients reflects a difference in the behaviour of the mean age of the stellar population along barred and unbarred galaxies; galaxies with zero or positive color gradients show a slight tendency of having larger bulges, with a greater central concentration of light, and we confirm the correlation between the scale lengths of bulges and disks. These results are compatible and favourable to the secular evolutionary scenario, in which stellar bars induce radial mass fluxes to the central regions of galaxies. (Abridged)