Do dwarf spheroidal galaxies contain dark matter?

Abstract

The amount of dark matter in the four galactic dwarf spheroidals with large mass-to-light ratios is investigated. Sextans has a cut-off radius which is equal to the expected tidal radius, assuming a high mass-to-light ratio. This satellite very likely is dark matter dominated. Carina, Ursa Minor and Draco, on the other hand, cannot contain a dominating dark matter component if the observed 'extra-tidal' stars are located exterior to the tidal radii of these systems. The evidence for tidal stripping in the absence of dark matter is also supported by the fact that the observed cut-off radii of all three satellites are equal to their tidal radii, assuming a low, globular cluster like mass-to-light ratio. The large velocity dispersions of these galaxies, on the other hand, seem to provide strong evidence for a massive dark matter component. In this case, the 'extra-tidal' stars lie deeply embedded in the dark matter potential wells of the satellites. These stars then would represent a gravitationally bound, extended stellar component with unknown origin.