Velocity dispersions and mass-to-light ratios for elliptical galaxies

Abstract

Velocity dispersions for 25 E and S0 galaxies are presented which were measured by employing conventional and Fourier techniques to reduce spectral data obtained in scans of the nuclear regions with an image-dissector scanner. The estimates are based primarily on certain sensitive blends near the Mg b triplet and also on the width of the Na D line. Nuclear values of the mass-to-light ratio (M/L(B)) are calculated using measured values of core radii and central surface brightnesses for several of the sampled galaxies, and it is found that the mean value of M/L(B) for giant ellipticals with an absolute bolometric magnitude of less than -20 is 7(H/50) in solar units. This value agrees well with the values for early-type spirals, implies that there is no large discontinuity in M/L between early-type spirals and ellipticals, and constitutes evidence against a stellar population strongly enriched in M-dwarfs. Both velocity dispersion and M/L(B) are found to be correlated with absolute magnitude for normal ellipticals, and the observed increase in M/L(B) is shown to be consistent with an increase in metal abundance with luminosity. It is concluded that ellipticals are close to being a one-parameter family with total mass as the most important independent variable.