Stellar populations of bulges in 14 cluster disc galaxies

Photometry and long-slit spectroscopy are presented for 14 S0 and spiral galaxies of the Fornax, Eridanus and Pegasus cluster, and NGC 7582 group. The structural parameters of the galaxies are derived from the R-band images by performing a two-dimensional photometric decomposition of the surface brightness distribution. This is assumed to be the sum of the contribution of a bulge and disc component characterized by elliptical and concentric isophotes with constant (but possibly different) ellipticity and position angles. The rotation curves and velocity dispersion profiles are measured from the spectra obtained along the major axis of galaxies. The radial profiles of the H beta, Mg and Fe line-strength indices are presented too. Correlations between the central values of Mg(2), (Fe), H beta and sigma or are found. The age, metallicity and alpha/Fe enhancement of the stellar population in the centre and at the radius where bulge and disc give the same contribution to the total surface brightness are obtained using stellar population models with variable element abundance ratios. Three classes of bulges are identified. The youngest bulges (similar to 2 Gyr) with ongoing star formation, intermediate-age bulges (4-8 Gyr) have solar metallicity, and old bulges (similar to 10 Gyr) have high metallicity. Most of the sample bulges display solar alpha/Fe enhancement, no gradient in age and a negative gradient of metallicity. The presence of negative gradient in the metallicity radial profile favours a scenario with bulge formation via dissipative collapse. This implies strong inside-out formation that should give rise to a negative gradient in the alpha/Fe enhancement too. But, no gradient is measured in the [alpha/Fe] radial profiles for all the galaxies, except for NGC 1366. In this galaxy there is a kinematically decoupled component, which is younger than the rest of host bulge. It possibly formed by enriched material probably acquired via interaction or minor merging. The bulge of NGC 1292 is the most reliable pseudo-bulge of our sample. The properties of its stellar population are consistent with a slow build-up within a scenario of secular evolution.