Two-Component Stellar Systems: Phase -Space Constraints
Abstract
In the context of the study of the properties of the mutual mass distribution of the bright and dark matter in bulges (or elliptical galaxies), the properties of the analitycal phase-space distribution function (DF) of two-component spherical self-consistent stellar systems, where one density distribution follows the Hernquist profile, and the other a "gamma=0" model, with different total masses and core radii (H0 models), presented in Ciotti (1999), are here summarized. A variable amount of radial Osipkov-Merritt orbital anisotropy is allowed in both components. The necessary and sufficient conditions that the model parameters must satisfy in order to correspond to a model where each one of the two distinct components has a positive DF (the so-called model consistency) are analytically derived, together with some results on the more general problem of the consistency of two-component "gamma=1+gamma=2" models. The possibility to add in a consistent way a black hole at the center of radially anisotropic "gamma models" is also discussed. In the particular case of H0 models, it is proved that a globally isotropic Hernquist component is consistent for any mass and core radius of the superimposed "gamma=0" halo; on the contrary, only a maximum value of the core radius is allowed to the $\gamma=0$ component when a Hernquist halo is added. The combined effect of halo concentration and orbital anisotropy is successively investigated. It is suggested that the observed centrally steep density profiles of bulges (and ellipticals as well) can be a natural consequence of the underlying dark matter distribution, if this is distributed similarly to, e.g., the ``universal'' profile of Navarro, Frenk, and White (1997).
- Publication:
-
The Formation of Galactic Bulges
- Pub Date:
- 1999
- DOI:
- 10.48550/arXiv.astro-ph/9812118
- arXiv:
- arXiv:astro-ph/9812118
- Bibcode:
- 1999fgb..conf..140C
- Keywords:
-
- Astrophysics
- E-Print:
- 4 pages, 0 figures, uses cupconf.sty. To appear on the proceedings of the STScI workshop ``When and how do bulges form and evolve?'' (5-7 October, 1998)