Mutual sensitivity of halo and disk parameters in a two‐component model

Abstract

AbstractThe mutual interaction between galactic dark halos and visible matter are explored by modelling a galaxy as two homogeneous, concentric and coaxial spheroidal subsystems, one completely lying within the other. The tensor virial theorem in its extended appropriate form is used and a general method outlined, then an application to the Galaxy is done. The values of equatorial semiaxis and axis ratio of the bright subsystem, and of the velocity components of both subsystems, deduced from a number of known observational data, are used in the computations as input parameters. Discussing the results, special effort has been devoted to the mutual sensitivity of halo and disk parameters which we understand in a twofold manner: 1) numerical interdependence between the present parameters of the visible Galaxy and the ones of dark matter, and 2) dependence of the bright component evolution on the characteristics of the dark halo, in which the former was embedded since the beginning. At present, due to the smallness of dark matter inside the bright disk, the halo‐disk interaction is so weak that few informations can be obtained; consequently, the solutions for dark masses and their axis ratios vary in a large range. Nevertheless, if one demands a spherical and isotropic halo, then from ad = 90 kpc a dark mass Md = 1.5 · 1012 M⊙ results in agreement with other independent estimations. Probably this was not the situation in the past when the disk was bigger and contained more dark mass. The dependence on Md/Mb and εd/εb was likely affecting the star formation rate and in this way contributing to the present morphology of the Galaxy and other galaxies.