2010MNRAS.403.2143H

We present a survey, using the Chandra X-ray observatory, of the central gravitating mass profiles in a sample of 10 galaxies, groups and clusters, spanning ∼2 orders of magnitude in virial mass. We find the total mass distributions from ∼0.2 to 10R_e, where R_eis the optical effective radius of the central galaxy, are remarkably similar to power-law density profiles. The negative logarithmic slope of the mass density profiles, α, systematically varies with R_e, from α ≃ 2, for systems with R_e∼ 4kpc to α ≃ 1.2 for systems with R_e≳ 30kpc. Departures from hydrostatic equilibrium are likely to be small and cannot easily explain this trend. We show that the conspiracy between the baryonic (Sersic) and dark matter (Navarro-Frenk-White/Einasto) components required to maintain a power-law total mass distribution naturally predicts an anti-correlation between α and R_ethat is very close to what is observed. The systematic variation of α with R_e implies a dark matter fraction within R_ethat varies systematically with the properties of the galaxy in such a manner as to reproduce, without fine tuning, the observed tilt of the Fundamental Plane. We speculate that establishing a nearly power-law total mass distribution is therefore a fundamental feature of galaxy formation and the primary factor which determines the tilt of the Fundamental Plane.