Bars rejuvenating bulges? Evidence from stellar population analysis
  We obtained stellar ages and metallicities via spectrum fitting for a sample
of 575 bulges with spectra available from the Sloan Digital Sky Survey. The
structural properties of the galaxies have been studied in detail in Gadotti
(2009b) and the sample contains 251 bulges in galaxies with bars. Using the
whole sample, where galaxy stellar mass distributions for barred and unbarred
galaxies are similar, we find that bulges in barred and unbarred galaxies
occupy similar loci in the age vs. metallicity plane. However, the distribution
of bulge ages in barred galaxies shows an excess of populations younger than ~
4 Gyr, when compared to bulges in unbarred galaxies. Kolmogorov-Smirnov
statistics confirm that the age distributions are different with a significance
of 99.94%. If we select sub-samples for which the bulge stellar mass
distributions are similar for barred and unbarred galaxies, this excess
vanishes for galaxies with bulge mass log M < 10.1 M_Sun while for more massive
galaxies we find a bimodal bulge age distribution for barred galaxies only,
corresponding to two normal distributions with mean ages of 10.4 and 4.7 Gyr.
We also find twice as much AGN among barred galaxies, as compared to unbarred
galaxies, for low-mass bulges. By combining a large sample of high quality data
with sophisticated image and spectral analysis, we are able to find evidence
that the presence of bars affect the mean stellar ages of bulges. This lends
strong support to models in which bars trigger star formation activity in the
centers of galaxies.
