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5.5. Galaxy Halos

Ostriker & Peebles [105] suggested that the existence of massive halos around spiral galaxies was needed in order for the disks to be stable against bar formation. Their paper led Lecar [84] to suggest that the diffuse dark matter in Coma comes from tidally torn-off halos. Indeed, the lack of significant luminosity segregation of Coma galaxies may indicate that they have lost their massive halos very early in the history of the cluster (see Section 6.1).

Support to his model came from the observations of Thompson [134], who showed that the density of barred galaxies is higher in the cluster centre, as predicted if these galaxies have indeed lost their halos.

Lecar's hypothesis would imply similar mass-to-light ratios for galaxies and clusters, and this is consistent with current estimates (e.g. Bahcall [11]).