Fundamental properties of elliptical galaxies

Abstract

The global properties of elliptical galaxies, such as luminosity, radius, projected velocity dispersion, projected luminosity, etc., form a two-dimensional family. This 'fundamental plane' of elliptical galaxies can be defined in observable terms by the velocity dispersion and mean surface brightness. Its thickness is given by the present measurement error bars, and there are no significant indications of nonlinearity or higher dimensionality. This is indicative of a strong regularity in the process of galaxy formation. The equations of the plane can be used as new, substantially improved distance indicators for elliptical galaxies. However, all morphological parameters which describe the shape of the light distribution (ellipticity, elippticity gradient, isophotal twist rate, slope of the surface brightness profile) and reflect dynamical anisotropies of stars are completely independent of this fundamental plane. Thus, the elliptical galaxies are actually a '2 + N' parameter family. The M/L ratios correlate only with the velocity dispersions and show a small intrinsic scatter, perhaps only about 30 percent, in a luminosity range spanning some four orders of magnitude; this suggests a constant fraction of the dark matter contribution in elliptical galaxies.