GALAXIES

The fundamental plane of early-type galaxies: Non-homology of the spatial structure

A&A, in press

CRAL-Observatoire de Lyon (CNRS: UMR 142), F-69561 Saint-Genis-Laval cedex, France

Abstract:
Parametrizing their light distribution with a Sérsic profile, we show that the non-homology in the structure of early-type galaxies has a measurable incidence on their scaling relations. Indeed, the S´rsic exponent (i.e., the shape of the photometric profile) correlates with the residuals to the Fundamental Plane. This correlation is in excellent agreement with the theoretical expectation for isotropic galaxies. Adding together the contributions of: (i) the stellar population, (ii) the rotational support, and (iii) the non-homology, fully accounts for the tilt of the Fundamental Plane. This supports the hypothesis of a constant stellar to dynamical mass ratio in the luminous region of early-type galaxies. We confirm the existence of relations between the Sérsic exponent, n, and the effective radius or the absolute magnitude, and we give indications for a saturation of this index for the bright (M_B < -20) or large (r_e > 6.3 kpc) galaxies at a value compatible with the de Vaucouleurs law (n=4).

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