No abstract

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 Hβ, Mg and Fe line‐strength indices are presented too. Correlations between the central values of Mg2, 〈Fe〉, Hβ and σ are found. The age, metallicity and α/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 (∼2 Gyr) with ongoing star formation, intermediate‐age bulges (4–8 Gyr) have solar metallicity, and old bulges (∼10 Gyr) have high metallicity. Most of the sample bulges display solar α/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 α/Fe enhancement too. But, no gradient is measured in the [α/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.

No abstract

No abstract

In order to investigate the correlation between the circular velocity V c and the central velocity dispersion of the spheroidal component σ c , we analyzed these quantities for a sample of 40 high surface brightness disc galaxies (hereafter HSB), 8 giant low surface brightness spiral galaxies (hereafter LSB), and 24 elliptical galaxies characterized by flat rotation curves. Galaxies have been selected to have a velocity gradient ≤ 2 km s −1 kpc −1 for R ≥ 0.35R 25 . We used these data to better define the previous V c -σ c correlation for spiral galaxies (which turned out to be HSB) and elliptical galaxies, especially at the lower end of the σ c values. We find that the V c -σ c relation is described by a linear law out to velocity dispersions as low as σ c ≈ 50 km s −1 , while in previous works a power law was adopted for galaxies with σ c > 80 km s −1 .Elliptical galaxies with V c based on dynamical models or directly derived from the H I rotation curves follow the same relation as the HSB galaxies in the V c -σ c plane. On the contrary, the LSB galaxies follow a different relation, since most of them show either higher V c (or lower σ c ) with respect to the HSB galaxies. This argues against the relevance of baryon collapse in the radial density profile of the dark matter haloes of LSB galaxies. Moreover, if the V c -σ c relation is equivalent to one between the mass of the dark matter halo and that of the supermassive black hole, these results suggest that the LSB galaxies host a supermassive black hole with a smaller mass compared to HSB galaxies of equal dark matter halo. On the other hand, if the fundamental correlation of SMBH mass is with the halo circular velocity, then LSBs should have larger black hole masses for given bulge dispersion.Elliptical galaxies with V c derived from H I data and LSB galaxies were not considered in previous studies.