Authors: Alister W. Graham, David Merritt, Ben Moore, Juerg Diemand, Balsa Terzic
Abstract: We have recently shown that the 3-parameter density-profile model from Prugniel & Simien provides a better fit to simulated, galaxy- and cluster-sized, dark matter halos than an NFW-like model with arbitrary inner profile slope γ (Paper I). By construction, the parameters of the Prugniel-Simien model equate to those of the Sersic R1/n function fitted to the projected distribution. Using the Prugniel-Simien model, we are therefore able to show that the location of simulated (1012 Msun) galaxy-sized dark matter halos in the μe-log Re diagram coincides with that of brightest cluster galaxies, i.e., the dark matter halos appear consistent with the Kormendy relation defined by luminous elliptical galaxies. These objects are also seen to define the new relation log(ρe) = 0.5 - 2.5log(Re), in which ρe is the internal density at r=Re. Simulated (1014.5 Msun) cluster-sized dark matter halos and the gas component of real galaxy clusters follow the relation log(ρe) = 2.5[1 - log(Re)].
Given the shapes of the various density profiles, we are able to conclude that while dwarf elliptical galaxies and galaxy clusters can have dark matter halos with effective radii of comparable size to the effective radii of their baryonic component, luminous elliptical galaxies can not. For increasingly large elliptical galaxies - with increasingly large (stellar) profile shapes `n' - to be dark matter dominated at large radii requires dark matter halos with increasingly large effective radii compared to the effective radii of their stellar component.