Journal Article

The slope of the mass profile and the tilt of the Fundamental Plane in early-type galaxies

Philip J. Humphrey and David A. Buote

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 403, issue 4, pages 2143-2151
Published in print April 2010 | ISSN: 0035-8711
Published online April 2010 | e-ISSN: 1365-2966 | DOI:
The slope of the mass profile and the tilt of the Fundamental Plane in early-type galaxies

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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 10Re, where Re is 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 Re, from α≃ 2, for systems with Re∼ 4 kpc to α≃ 1.2 for systems with Re≳ 30 kpc. 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 Re that is very close to what is observed. The systematic variation of α with Re implies a dark matter fraction within Re that 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.

Keywords: galaxies: elliptical and lenticular, cD; galaxies: fundamental parameters; galaxies: ISM; dark matter; Xrays: galaxies

Journal Article.  7068 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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