The contribution of rotational velocity to the FP of elliptical galaxies

¹ Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy e-mail: andrea.riciputi@bo.astro.it
² INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
³ Department of Astronomy & Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON, M5S 3H8, Canada

Received: 7 June 2005
Accepted: 28 July 2005

Abstract

The contribution of ordered rotation to the observed tilt and thickness of the Fundamental Plane of elliptical galaxies is studied by means of oblate, two-integrals cuspy galaxy models with adjustable flattening, variable amount of ordered rotational support, and possible presence of a dark matter halo and of a central super-massive black hole. We find that, when restricting the measure of the velocity dispersion to the central galactic regions, rotation has a negligible effect, and so cannot be responsible of the observed tilt. However, streaming velocity effect can be significant when observing small and rotationally supported galaxies through large (relative) aperture (as for example in Fundamental Plane studies at high redshift), and can lead to unrealistically low mass-to-light ratios. The effect of a central supermassive black hole on the kinematical fields, and the models position in the -ellipticity plane are also discussed.