51 research outputs found
A Possible Solution for the Relation of Globular Clusters in M31. II. the Age-Metallicity Relation
This is the second of a series of papers in which we present a new solution
to reconcile the prediction of single stellar population (SSP) models with the
observed stellar mass-to-light () ratios of globular clusters (GCs) in M31
and its trend with respect to . In the present work our focus
is on the empirical relation between age and metallicity for GCs and its effect
on the ratio. Assuming that there is an anti-correlation between the age
of M31 GCs and their metallicity, we evolve dynamical SSP models of GCs to
establish a relation between the ratio (in the and band) and
metallicity. We then demonstrate that the established
relation is in perfect agreement with that of M31 GCs. In our models we
consider both the canonical initial mass function (IMF) and the top-heavy IMF
depending on cluster birth density and metallicity as derived independently
from Galactic GCs and ultra-compact dwarf galaxies by Marks et al. Our results
signify that the combination of the density- and metallicity-dependent
top-heavy IMF, the anti-correlation between age and metallicity, stellar
evolution and standard dynamical evolution yields the best possible agreement
with the observed trend of for M31 GCs.Comment: 8 pages, 4 figures, 1 table. Accepted for publication in Ap
Evolution of star clusters on eccentric orbits: semi-analytical approach
We study the dynamical evolution of star clusters on eccentric orbits using a
semi-analytical approach. In particular we adapt and extend the equations of
EMACSS code, introduced by Gieles et al. (2014), to work with eccentric orbits.
We follow the evolution of star clusters in terms of mass, half-mass radius,
core radius, Jacobi radius and the total energy over their dissolution time.
Moreover, we compare the results of our semi-analytical models against -body
computations of clusters with various initial half-mass radius, number of stars
and orbital eccentricity to cover both tidally filling and under-filling
systems. The evolution profiles of clusters obtained by our semi-analytical
approach closely follow those of -body simulations in different evolutionary
phases of star clusters, from pre-collapse to post-collapse. Given that the
average runtime of our semi-analytical models is significantly less than that
of -body models, our approach makes it feasible to study the evolution of
large samples of globular clusters on eccentric orbits.Comment: 11 pages, 4 figures, 1 table. Accepted for publication in MNRA
Identifying the possible ex-situ origin of the globular clusters of the Milky Way: A kinematic study
This is the second paper in a series, which studies the likelihood that some
globular clusters (GCs) of the Milky Way (MW) could have originated from a
dwarf satellite galaxy (DSG). Using a large suite of three-body simulations we
determine the present-day orbital properties of 154 GCs that could have escaped
from 41 MW DSGs over the past . For the MW we considered two
sets of static and dynamic models which account for the sustained growth of the
MW since its birth. We focus on the Magellanic Clouds and Sagittarius. We
compare the apogalactic distance, eccentricity, and orbital inclination of the
MW GCs with those of runaway GCs from DSGs, to constrain their possible ex-situ
origin. We observe a positive correlation between a DSG mass and the dispersion
of its runaway GCs in the orbital parameter space of (, ). We
provide tables of the identified MW GCs and their likely associated
progenitors. In total, we find 29 (19%) MW GCs which could be kinematically
associated with MW DSGs. We report, for the first time, 6 and 10 new
associations with the Large Magellanic Cloud and the Sagittarius, respectively.
For the Sagittarius we predict a concentration of runaway GCs at large
apogalactic distances of ,
, and a relative inclination of .
So far, there has not been any observed GCs with such orbital elements.
Complemented with photometric and spectroscopic observations, and cosmological
simulations, the findings from the present study could conclusively settle the
debate over the in-situ vs. ex-situ origin of the MW GCs.Comment: 20 pages, 16 figures, 5 tables, references amended. Accepted for
publication in MNRA
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