The role of bars on bulge formation and the evolution of barred galaxies

Abstract

We have started a long term project to analyse the role played by bars in bulge formation and the formation and evolution of bars from the point of view of their star formation histories and stellar populations. To this aim, we have obtained high S/N long slit spectra of 22 barred galaxies, ranging in morphological types between S0 to Sb galaxies. We have obtained Lick/IDS indices along the bar for all the sample galaxies. We used Vazdekis et al. (2007) models to derive simple stellar population ages and metallicities. Extreme care has been taken to correct the indices for any nebular contribution. Preliminary results show that the bulges of barred galaxies are similar to those of unbarred galaxies. The metalicity gradients along bars show a dependency with the central stellar velocity dispersion. The galaxies with higher central dispersion appear to have a gradient in both age and metallicity changing radially outward to a younger and more metal rich population. The galaxies with lower central velocity dispersion show a change in age and metallicity with respect to the inner part of the bar with the populations at the end of the bar being younger or same age and more metal poor. There is no correlation between the gradient and the morphological or nuclear type. There is no correlation either with the total K-band luminosity. The fact that we observe galaxies with the outer parts of the bar more metal rich than the inner parts shows that at least some bars are old, since it requires long time for the observed enrichment to take place. The gradients in these bars are opposite to what is generally found in disks. The correlation between the central velocity dispersion and the bar gradient relates both, the dynamical and stellar population aging of the bar.