A simple two-component description of energy equipartition and mass
  segregation for anisotropic globular clusters
  In weakly collisional stellar systems such as some globular clusters, partial
energy equipartition and mass segregation are expected to develop as a result
of the cumulative effect of stellar encounters even in systems initially
characterized by star-mass independent density and energy distributions. In
parallel, numerical simulations have demonstrated that radially-biased pressure
anisotropy slowly builds up in realistic models of globular clusters from
initial isotropic conditions, leading to anisotropy profiles that, to some
extent, mimic those resulting from incomplete violent relaxation known to be
relevant to elliptical galaxies. In this paper we consider a set of realistic
simulations realized by means of Monte Carlo methods and analyze them by means
of self-consistent two-component models. For the purpose, we refer to an
underlying distribution function, originally conceived to describe elliptical
galaxies, that has been recently truncated and adapted to the context of
globular clusters. The two components are meant to represent light stars
(combining all main sequence stars) and heavy stars (giants, dark remnants, and
binaries). We show that this conceptually simple family of two-component
truncated models provides a reasonable description of simulated density,
velocity dispersion, and anisotropy profiles, especially for the most relaxed
systems, with the capability to express quantitatively the attained levels of
energy equipartition and mass segregation. In contrast, two-component isotropic
models based on the King distribution function do not offer a comparably
satisfactory representation of the simulated globular clusters. With this work
we provide a new reliable diagnostic tool applicable to nonrotating globular
clusters that are characterized by significant gradients in the local value of
the mass-to-light ratio, beyond the commonly used one-component dynamical
models.
