Bars and Bulges Through Masks of Time

Abstract

We present here some of the results of a project devoted to understand the influence of bars in the evolution of galaxy disks through the study of their stellar content. First, we present the results on the derived stellar parameters for intermediate age populations, traced by Lick/IDS indices along the bar for a sample of 20 galaxies as well as the disk population parameters obtained from the whole spectra of 4 galaxies. Second, we present the results of the detail current and recent (<1 Gyr) star formation properties of two barred galaxies, NGC 2903 and NGC 1530. For the intermediate populations, we have obtained high S/N long-slit spectra of 20 barred galaxies, ranging in morphological types between S0 and Sb galaxies. We have derived Lick/IDS indices along the bar for all the sample galaxies. We find three types of bars according to their metallicity gradient: bars with negative metallicity gradient, bars with null metallicity gradient, and galaxies with positive metallicity gradient. Regarding the bulge region we find that the ages and metallicities are younger and more metal rich, at a given σ, than the bulges of unbarred galaxies. The bulges of the barred galaxies in our sample have suffered a different chemical enrichment history compared to unbarred galaxies of the same morphological types, same σ distribution, and same inclinations. We have also analyzed the kinematics star formation history of the disk region (2–3 disk scale lengths) for a sample of four barred galaxies. Most of the stellar mass in all the four galaxies is composed of old stars, this also true at large radii. However, a larger fraction of young stars is present in the external parts compared to the inner disk, compatible with a mild inside-out growing. The young stars all across the galaxy show lower metal content, favoring a scenario where stars are forming from recently accreted gas from the halo. Finally, we find some curious properties regarding the massive star forming regions on the two galaxies analyzed, NGC 2903 and NGC 1530. There are indications that massive stars are forming on the trailing side of the bar dust lane, and they age as they cross the bar ofNGC 1530. We have found the presence of a large area of the bar of NGC 2903 containing older, with respect to the other star-forming regions present in the bar (a few hundred of Myrs) ultraviolet-emitting knots without significant Hα nor 24 μm emission, indicating regions that are not currently favored by the bar to form stars.