The Kinetic Energy in Elliptical Galaxies

Abstract

Listen

Translate article

In order to understand the true physical status of the elliptical galaxies, it is needed to evaluate the contribution of the rotational and of the residual motions to the total kinetic energy of the system. A procedure to derive the two terms of the kinetic energy from the observed velocity dispersion profile (VDP) and the rotation curve (RC) is proposed. It is assumed that E galaxies are spheroidal systems and that their rotation axes are perpendicular to the line of sight. The spatial luminosity distribution given by Mellier and Mathefc (1987) was adopted. The deprojection of the observed VDP and RC is performed by fitting the observed quantities to suitable analytical expressions, and then by solving the corresponding Abel integral equations. The kinetic energies per unit mass are then computed assuming spheroidal symmetry for the σ(\(\bar r\)) and cylindrical simmetry for the V(\(\bar r\)). To obtain the total kinetic energy due to random motions, hypotheses on the anysotropy of the velocity field need to be made, but the true value is not far from the one obtained by assuming isotropy (Busarello et al, 1988, Busarello and Longo, 1989). The total mass can be derived from the virial theorem taking in to account the ellipticity of the density distribution (Busarello et al., 1988). The contribution to the total mass of the rotational kinetic energy is not negligible. The results for the original data for the 10 faint ellipticals in the sample by Davies et al. (1983), are given in table 1 (column 4 and 5 give the V/σ values by us and by Davies et al. (1983), respectively, while column 6 gives the ratios M/r e ).