Homogenization of the Stellar Population along Late-Type Spiral Galaxies

We present a study of the broadband UBV color profiles for 257 Sbc barred andnon-barred galaxies. In our sample, the color gradients are negative (reddishinward) in approximately 59% of the objects, are almost null in 27%, and arepositive in 14%, considering only the face-on galaxies, which representapproximately 51% of the sample. We have also found that barred galaxies areover-represented among the objects having null or positive gradients,indicating that bars act as a mechanism of homogenization of the stellarpopulation. A correlation between the total and bulge colors was found, whichis a consequence of an underlying correlation between the colors of bulges anddisks found by others. Moreover, the mean total color is the same irrespectiveof the gradient regime, while bulges are bluer in galaxies with null orpositive gradients, which indicates an increase of the star formation rate inthe central regions of these objects. We found no correlation between color andO/H abundance gradients. We discuss this result considering a picture in whichbars are a relatively fast recurrent phenomenon. These results are notcompatible with a pure classical monolithic scenario for bulge and diskformation. On the contrary, they favor a scenario where both these componentsare evolving in a correlated process, in which stellar bars play a crucialrole.(Abridged)Comment: Accepted for publication in The Astronomical Journal; 43 pages, 9 figures, 6 table