128 research outputs found
On a possible origin for the lack of old star clusters in the Small Magellanic Cloud
We model the dynamical interaction between the Small and Large Magellanic
Clouds and their corresponding stellar cluster populations. Our goal is to
explore whether the lack of old clusters ( Gyr) in the Small
Magellanic Cloud (SMC) can be the result of the capture of clusters by the
Large Magellanic Cloud (LMC), as well as their ejection due to the tidal
interaction between the two galaxies. For this purpose we perform a suite of
numerical simulations probing a wide range of parameters for the orbit of the
SMC about the LMC. We find that, for orbital eccentricities ,
approximately 15 per cent of the SMC clusters are captured by the LMC. In
addition, another 20 to 50 per cent of its clusters are ejected into the
intergalactic medium. In general, the clusters lost by the SMC are the less
tightly bound cluster population. The final LMC cluster distribution shows a
spatial segregation between clusters that originally belonged to the LMC and
those that were captured from the SMC. Clusters that originally belonged to the
SMC are more likely to be found in the outskirts of the LMC. Within this
scenario it is possible to interpret the difference observed between the star
field and cluster SMC Age-Metallicity Relationships for ages Gyr.Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letter
And yet it moves: The dangers of artificially fixing the Milky Way center of mass in the presence of a massive Large Magellanic Cloud
Motivated by recent studies suggesting that the Large Magellanic Cloud (LMC)
could be significantly more massive than previously thought, we explore whether
the approximation of an inertial Galactocentric reference frame is still valid
in the presence of such a massive LMC. We find that previous estimates of the
LMC's orbital period and apocentric distance derived assuming a fixed Milky Way
are significantly shortened for models where the Milky Way is allowed to move
freely in response to the gravitational pull of the LMC. Holding other
parameters fixed, the fraction of models favoring first infall is reduced. Due
to this interaction, the Milky Way center of mass within the inner 50 kpc can
be significantly displaced in phase-space in a very short period of time that
ranges from 0.3 to 0.5 Gyr by as much as 30 kpc and 75 km/s. Furthermore, we
show that the gravitational pull of the LMC and response of the Milky Way are
likely to significantly affect the orbit and phase space distribution of tidal
debris from the Sagittarius dwarf galaxy (Sgr). Such effects are larger than
previous estimates based on the torque of the LMC alone. As a result, Sgr
deposits debris in regions of the sky that are not aligned with the present-day
Sgr orbital plane. In addition, we find that properly accounting for the
movement of the Milky Way around its common center of mass with the LMC
significantly modifies the angular distance between apocenters and tilts its
orbital pole, alleviating tensions between previous models and observations.
While these models are preliminary in nature, they highlight the central
importance of accounting for the mutual gravitational interaction between the
MW and LMC when modeling the kinematics of objects in the Milky Way and Local
Group.Comment: Accepted for publication in ApJ; 16 pages, 11 figure
Neutron star mergers and rare core-collapse supernovae as sources of r-process enrichment in simulated galaxies
We use cosmological, magnetohydrodynamical simulations of Milky Way-mass
galaxies from the Auriga project to study their enrichment with rapid neutron
capture (r-process) elements. We implement a variety of enrichment models from
both binary neutron star mergers and rare core-collapse supernovae. We focus on
the abundances of (extremely) metal-poor stars, most of which were formed
during the first ~Gyr of the Universe in external galaxies and later accreted
onto the main galaxy. We find that the majority of metal-poor stars are
r-process enriched in all our enrichment models. Neutron star merger models
result in a median r-process abundance ratio which increases with metallicity,
whereas the median trend in rare core-collapse supernova models is
approximately flat. The scatter in r-process abundance increases for models
with longer delay times or lower rates of r-process producing events. Our
results are nearly perfectly converged, in part due to the mixing of gas
between mesh cells in the simulations. Additionally, different Milky Way-mass
galaxies show only small variation in their respective r-process abundance
ratios. Current (sparse and potentially biased) observations of metal-poor
stars in the Milky Way seem to prefer rare core-collapse supernovae over
neutron star mergers as the dominant source of r-process elements at low
metallicity, but we discuss possible caveats to our models. Dwarf galaxies
which experience a single r-process event early in their history show highly
enhanced r-process abundances at low metallicity, which is seen both in
observations and in our simulations. We also find that the elements produced in
a single event are mixed with ~10^8 Msun of gas relatively quickly,
distributing the r-process elements over a large region.Comment: Accepted for publication in MNRAS. Revised version: added Figure 13
(on mixing of iron and r-process elements) and an Appendix (on iron and
magnesium abundances) and updated the r-process yields (Tables 1 and 2 and
normalization of abundances
Selecting ultra-faint dwarf candidate progenitors in cosmological N-body simulations at high redshifts
The smallest satellites of the Milky Way ceased forming stars during the
epoch of reionization and thus provide archaeological access to galaxy
formation at . Numerical studies of these ultra-faint dwarf galaxies
(UFDs) require expensive cosmological simulations with high mass resolution
that are carried out down to . However, if we are able to statistically
identify UFD host progenitors at high redshifts \emph{with relatively high
probabilities}, we can avoid this high computational cost. To find such
candidates, we analyze the merger trees of Milky Way type halos from the
high-resolution suite of dark matter only simulations.
Satellite UFD hosts at are identified based on four different abundance
matching (AM) techniques. All the halos at high redshifts are traced forward in
time in order to compute the probability of surviving as satellite UFDs today.
Our results show that selecting potential UFD progenitors based solely on their
mass at z=12 (8) results in a 10\% (20\%) chance of obtaining a surviving UFD
at in three of the AM techniques we adopted. We find that the progenitors
of surviving satellite UFDs have lower virial ratios (), and are
preferentially located at large distances from the main MW progenitor, while
they show no correlation with concentration parameter. Halos with favorable
locations and virial ratios are times more likely to survive as
satellite UFD candidates at Comment: 12 pages, 7 figures, accepted for publication at MNRAS after minor
revision
The Caterpillar Project: A Large Suite of Milky Way Sized Halos
We present the largest number of Milky Way sized dark matter halos simulated
at very high mass ( M/particle) and temporal resolution
(5 Myrs/snapshot) done to date, quadrupling what is currently available
in the literature. This initial suite consists of the first 24 halos of the
(www.caterpillarproject.org) whose project goal of 60 -
70 halos will be made public when complete. We resolve 20,000
gravitationally bound subhalos within the virial radius of each host halo. Over
the ranges set by our spatial resolution our convergence is excellent and
improvements were made upon current state-of-the-art halo finders to better
identify substructure at such high resolutions (e.g., on average we recover
4 subhalos in each host halo above 10 M which would have
otherwise not been found using conventional methods). For our relaxed halos,
the inner profiles are reasonably fit by Einasto profiles ( = 0.169
0.023) though this depends on the relaxed nature and assembly history of
a given halo. Averaging over all halos, the substructure mass fraction is
, and mass function slope is d/d though we find scatter in the normalizations for fixed halo
mass due to more concentrated hosts having less subhalos at fixed subhalo mass.
There are no biases stemming from Lagrangian volume selection as all Lagrangian
volume types are included in our sample. Our detailed contamination study of
264 low resolution halos has resulted in obtaining very large and
unprecedented, high-resolution regions around our host halos for our target
resolution (sphere of radius Mpc) allowing for accurate
studies of low mass dwarf galaxies at large galactocentric radii and the very
first stellar systems at high redshift ( 10).Comment: 19 pages; 14 figures; 6 tables; Received September 3, 2015; Accepted
November 15, 2015; Published February 2, 201
On a possible origin for the lack of old star clusters in the small magellanic cloud
We model the dynamical interaction between the Small and LargeMagellanic Clouds and their corresponding stellar cluster populations.Our goal is to explorewhether the lack of old clusters (≳7 Gyr) in the Small Magellanic Cloud (SMC) can be the result of the capture of clusters by the Large Magellanic Cloud (LMC) as well as their ejection due to the tidal interaction between the two galaxies. For this purpose, we perform a suite of numerical simulations probing a wide range of parameters for the orbit of the SMC about the LMC.We find that, for orbital eccentricities e ≥ 0.4, approximately 15 per cent of the SMC clusters are captured by the LMC. In addition, another 20-50 per cent of its clusters are ejected into the intergalactic medium. In general, the clusters lost by the SMC are the less tightly bound cluster population. The final LMC cluster distribution shows a spatial segregation between clusters that originally belonged to the LMC and those that were captured from the SMC. Clusters that originally belonged to the SMC are more likely to be found in the outskirts of the LMC. Within this scenario, it is possible to interpret the difference observed between the star field and cluster SMC age-metallicity relationships for ages ≳7Gyr.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
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