On the universality of the global slope -- anisotropy inequality

Recently, some intriguing results have lead to speculations whether the central density slope -- velocity dispersion anisotropy inequality (An & Evans) actually holds at all radii for spherical dynamical systems. We extend these studies by providing a complete analysis of the global slope -- anisotropy inequality for all spherical systems in which the augmented density is a separable function of radius and potential. We prove that these systems indeed satisfy the global inequality if their central anisotropy is $\beta_0\leq 1/2$. Furthermore, we present several systems with $\beta_0 > 1/2$ for which the inequality does not hold, thus demonstrating that the global density slope -- anisotropy inequality is not a universal property. This analysis is a significant step towards an understanding of the relation for general spherical systems.Comment: 8 pages, 1 figure, accepted for publication in Ap

The dynamical structure of dark matter halos with universal properties

N-body simulations have unveiled several apparently universal properties of dark matter halos, including a cusped density profile, a power-law pseudo-phase-space density rho/sigma(3)(r), and a linear beta-gamma relation between the density slope and the velocity anisotropy. We present a family of self-consistent phase-space distribution functions (DFs) F(E, L), based on the Dehnen-McLaughlin Jeans models, that incorporate these universal properties very accurately. These DFs, derived using a quadratic programming technique, are analytical, positive, and smooth over the entire phase space and are able to generate four-parameter velocity anisotropy profiles beta(r) with arbitrary asymptotic values beta(0) and beta(infinity). We discuss the orbital structure of six radially anisotropic systems in detail and argue that, apart from its use for generating initial conditions for N-body studies, our dynamical modeling provides a valuable complementary approach to understand the processes involved in the formation of dark matter halos

The conversion of late-type into early-type dwarf galaxies by ram-pressure stripping in the Fornax cluster

We put to the test the hypothesis that the Fornax cluster dwarf galaxies are mostly a relatively recently acquired population, of which the star-forming, late-type members are converted into quiescent, early-type ones by ram-pressure stripping while being on orbits that plunge inside the inner few hundred kiloparsecs of the cluster. We construct dynamical models with different anisotropy profiles for the dwarf galaxy population and show that only extremely radially anisotropic orbital distributions are in agreement with the available morphological, positional, and kinematical data, especially with the radially increasing late-to-early-type ratio. This corroborates the idea that the Fornax cluster dwarfs are an infall population and that environmental factors, in this case ram-pressure stripping, play a prominent role in converting late-type dwarfs into early-type ones