Abstract
This second lecture was dedicated to elliptical galaxies, and the determination of the amount of dark matter they harbor. These galaxies appear as flattened spheroids, but are not flattened by rotation, as one might at first think. The flattening is due to the anisotropy of the stellar velocity dispersion, probably resulting from the formation of these systems by the merging of smaller spiral galaxies. In the absence of rotation, it's velocity dispersion that should help us quantify dark matter. But this task is much more difficult than for spiral galaxies, as velocities are averaged over the line of sight, and we don't know how to de-project ellipticals. Are they flattened spheroids like patties (two equal major axes), or elongated like cigars (two equal minor axes), or even triaxial systems? A review is made of the various diagnostics that enable us to better understand this shape: isophoton rotation, amount of rotation in relation to velocity dispersion measured by the Doppler effect. Statistically, projection problems can be eliminated. Statistics reveal scaling relationships, notably the Faber-Jackson relationship, very similar to the Tully-Fischer relationship for spirals, but where dispersion replaces rotation.
