Multi-Component Models For Disc Galaxies

Abstract

We present an application of a new set of detailed, self-consistent, dynamical models for disc galaxies. We start from the hypothesis that each galaxy can be decomposed into a bulge, following the r1/4law, and a disc with an exponential projected density profile; and that the isodensity surfaces of each component can be represented by similar concentric spheroids. After taking into account both the asymmetric drift effects and the integration along the line of sight, we produce the rotational velocity and velocity-dispersion profile, andthe approximate shape of the line-of-sight velocity distributions for the stars as parameterized by the h3 and h4 coefficients of theGauss–Hermite expansion of the line profile. Photometric and kinematical data have been taken from the literature for the test case of the S0 galaxy NGC 5866, for which detailed stellar kinematical data are available at different positions across the galaxy. Apart from the innermost, dust-obscured regions of the galaxy, where observational effects are likely to be dominant, the model successfully reproduces the whole set of dynamical data available as well as giving a good fit to the photometry. The galaxy is shown to have an isotropic velocity-dispersion tensor, thus hinting at a dissipational formation process.