|Annu. Rev. Astron. Astrophys. 1994. 32:
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2.3. Elliptical Galaxies
The mass distribution in ellipticals can be probed by measuring the velocity dispersion of the stars and globular clusters. Unfortunately, the velocities do not determine the density profile uniquely and this method gives no evidence for dark matter within the central regions of ellipticals (de Zeeuw 1992), although the dynamics of globular clusters does provide evidence for dark matter around M87 (Huchra & Brodie 1987, Mould et al 1990). The best information therefore comes from X-ray observations of hot gas. These do, in fact, provide evidence for dark matter and, in many cases, one finds the same M ~ R law that characterizes spirals (Forman et al 1985, Sarazin 1986). Although these analyses assume that the gas is isothermal, usually one only has poor information on the temperature profile. However, Fabian et al (1986) obtain even larger minimum masses on the assumption that the halo is confined by a hydrostatic outer atmosphere. Giant ellipticals are sometimes the focus of cooling flows and this suggests that at least some of the dark matter in ellipticals may be baryonic (Fabian 1994).