OBSERVATIONS OF THE DYNAMICS OF 8 EARLY-TYPE GALAXIES

Velocity dispersion profiles and rotation curves have been measured for one lenticular and seven elliptical galaxies. Both direct and Fourier tech- niques were employed and the results of these two methods are in good agreement. An error analysis designed specifically for the Fourier quotient method gave a more accurate estimate of the uncertainties. The dependence of velocity dispersion on the normalizing line strength parameter is shown to be small. The low rotation velocities found by other authors are confirmed. All galaxies exhibit falling or constant values of velocity dispersion with increasing radius. The velocity dispersion profile of M87 is shown to be quali- tatively similar to other, more normal, elliptical galaxies.The two factors which determine the form of velocity dispersion profiles (the radial variation of the anisotropy of the stellar velocities and gradients in mass-to-light ratio) make a unique interpretation of these data difficult. However, galaxies showing dispersion profiles which fall more steeply than predicted by the isotropic models (e.g. NGC 3379) are likely to be dominated by radial motions at large radii. Those galaxies with flat dispersion profiles (e.g. NGC4697 and 4406) are most straightforwardly interpreted in terms of increasing values of the mass-to-light ratio with radius. © Royal Astronomical Society.