부산대학교 도서관

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2966.2008.14187.x Byline: Luca Ciotti (1★), Lucia Morganti (1) Keywords: black holes; stellar dynamics; galaxies: elliptical and lenticular, cD; dark matter Abstract: ABSTRACT It is well known that the density and anisotropy profile in the inner regions of a stellar system with positive phase-space distribution function (DF) are not fully independent. Here, we study the interplay between density profile and orbital anisotropy at large radii in physically admissible (consistent) stellar systems. The analysis is carried out by using two-component (n - [gamma], [gamma].sub.1) spherical self-consistent galaxy models, in which one density distribution follows a generalized [gamma] profile with external logarithmic slope n, and the other a standard [gamma].sub.1 profile (with external slope 4). The two density components have different 'core' radii, the orbital anisotropy is controlled with the Osipkov-Merritt recipe, and for simplicity we assume that the mass of the [gamma].sub.1 component dominates the total potential everywhere. The necessary and sufficient conditions for phase-space consistency are determined analytically, also in the presence of a dominant massive central black hole, and the analytical phase-space DF of (n - [gamma] ,1) models, and of n - [gamma] models with a central black hole, is derived for [gamma]= 0, 1, 2 . It is found that the density slope in the external regions of a stellar system can play an important role in determining the amount of admissible anisotropy: in particular, for fixed density slopes in the central regions, systems with a steeper external density profile can support more radial anisotropy than externally flatter models. This is quantified by an inequality formally identical to the 'cusp slope-central anisotropy' theorem by An & Evans, relating at all radii (and not just at the centre) the density logarithmic slope and the anisotropy indicator in all Osipkov-Merritt systems. Author Affiliation: (1)Astronomy Department, University of Bologna, via Ranzani 1, 40127 Bologna, Italy Article History: Accepted 2008 November 3. Received 2008 November 3; in original form 2008 October 1 Article note: (★E-mail: luca.ciotti@unibo.it) ([dagger]) Present address: Max-Planck-Institut fur extraterrestrische Physik, Giessenbachstra[sz]e, D-85741 Garching, Germany.