105 research outputs found
The Structural and Kinematic Evolution of Central Star Clusters in Dwarf Galaxies and Their Dependence on Dark Matter Halo Profiles
Through a suite of direct N-body simulations, we explore how the structural
and kinematic evolution of a star cluster located at the center of a dwarf
galaxy is affected by the shape of its host's dark matter density profile. The
stronger central tidal fields of cuspier halos minimize the cluster's ability
to expand in response to mass loss due to stellar evolution during its early
evolutionary stages and during its subsequent long-term evolution driven by
two-body relaxation. Hence clusters evolving in cuspier dark matter halos are
characterized by more compact sizes, higher velocity dispersions and remain
approximately isotropic at all clustercentric distances. Conversely, clusters
in cored halos can expand more and develop a velocity distribution profile that
becomes increasingly radially anisotropic at larger clustercentric distances.
Finally, the larger velocity dispersion of clusters evolving in cuspier dark
matter profiles results in them having longer relaxation times. Hence clusters
in cuspy galaxies relax at a slower rate and, consequently, they are both less
mass segregated and farther from complete energy equipartition than cluster's
in cored galaxies. Application of this work to observations allows for star
clusters to be used as tools to measure the distribution of dark matter in
dwarf galaxies and to distinguish isolated star clusters from ultra-faint dwarf
galaxies.Comment: 8 pages, 7 figures, Accepted for publication in MNRA
The complex kinematics of rotating star clusters in a tidal field
We broaden the investigation of the dynamical properties of tidally
perturbed, rotating star clusters by relaxing the traditional assumptions of
coplanarity, alignment, and synchronicity between the internal and orbital
angular velocity vector of their initial conditions. We show that the interplay
between the internal evolution of these systems and their interaction with the
external tidal field naturally leads to the development of a number of
evolutionary features in their three-dimensional velocity space, including a
precession and nutation of the global rotation axis and a variation of its
orientation with the distance from the cluster centre. In some cases, such a
radial variation may manifest itself as a counter-rotation of the outermost
regions relative to the inner ones. The projected morphology of these systems
is characterized by a non-monotonic ellipticity profile and, depending on the
initial inclination of the rotation axis, it may also show a twisting of the
projected isodensity contours. These results provide guidance in the
identification of non-trivial features which may emerge in upcoming
investigations of star cluster kinematics and a dynamical framework to
understand some of the complexities already hinted by recent observational
studies.Comment: 5 pages, 4 figures, accepted for publication in MNRA
Effects of massive central objects on the degree of energy equipartition of globular clusters
We present an analysis of the degree of energy equipartition in a sample of
101 Monte Carlo numerical simulations of globular clusters (GCs) hosting either
a system of stellar-mass black holes (BHS), an intermediate-mass black hole
(IMBH) or neither of them. For the first time, we systematically explore the
signatures that the presence of BHS or IMBHs produces on the degree of energy
equipartition and if these signatures could be found in current observations.
We show that a BHS can halt the evolution towards energy equipartition in the
cluster centre. We also show that this effect grows stronger with the number of
stellar-mass black holes in the GC. The signatures introduced by IMBHs depend
on how dominant their masses are to the GCs and for how long the IMBH has
co-evolved with its host GCs. IMBHs with a mass fraction below 2% of the
cluster mass produce a similar dynamical effect to BHS, halting the energy
equipartition evolution. IMBHs with a mass fraction larger than 2% can produce
an inversion of the observed mass-dependency of the velocity dispersion, where
the velocity dispersion grows with mass. We compare our results with
observations of Galactic GCs and show that the observed range of the degree of
energy equipartition in real clusters is consistent with that found in our
analysis. In particular, we show that some Galactic GCs fall within the
anomalous behaviour expected for systems hosting a BHS or an IMBH and are
promising candidates for further dynamical analysis.Comment: Accepted for publication in MNRAS. 14 pages, 11 figures. Main results
in Figures 2, 4 and 10 and their respective discussio
Investigating mass segregation process in globular clusters with Blue Straggler Stars: the impact of dark remnants
We present the results of a set of N-body simulations aimed at exploring how
the process of mass segregation (as traced by the spatial distribution of blue
straggler stars, BSSs) is affected by the presence of a population of heavy
dark remnants (as neutron stars and black holes). To this end, clusters
characterized by different initial concentrations and different fractions of
dark remnants have been modeled. We find that an increasing fraction of
stellar-mass black holes significantly delays the mass segregation of BSSs and
the visible stellar component. In order to trace the evolution of BSS
segregation, we introduce a new parameter () that can be easily measured
when the cumulative radial distribution of these stars and a reference
population are available. Our simulations show that might also be used as
an approximate indicator of the time remaining to the core collapse of the
visible component.Comment: ApJ accepte
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