DYNAMICAL EVIDENCE FOR DARK-MATTER

Dark matter has been studied dynamically on all scales from the solar system to superclusters. There is much less dark matter in the disk of the Milky Way than would be needed to explain the local rotation curve, but there is evidence far considerable dark matter in a flattened distribution. Three new results are discussed regarding dark matter on galactic scales: the dark halos of spirals appear to be flattened, elliptical galaxies have dark matter halos, and the halos of ellipticals have similar to 25% less mass than previously believed. Dark matter halos around spiral galaxies extend to greater than or similar to 200 kpc and perhaps to 1 or 2 Mpc. Previous measurements from galaxy motions indicating that clusters have large amounts of dark matter (Ohm similar to 0.2) are now confirmed by estimates derived from X-ray gas. Moreover, the measurements show that the mean speed of the galaxies and the gas particles is the same, indicating that the galaxy velocities are not 'biased'. Measurements of dark matter on the largest scales are qualitatively different from other dark matter measurements in that they generally derive from linearly perturbed (as opposed to virialized or relaxed) motions. Preliminary estimates show Ohm similar to 0.3-1 on these scales.