188 research outputs found
Limit on the LMC mass from a census of its satellites
We study the orbits of ultra-faint dwarf galaxies in the combined presence of
the Milky Way and LMC and we find 6 dwarfs which were likely accreted with the
LMC (Car 2, Car 3, Hor 1, Hyi 1, Phe 2, Ret 2), in addition to the SMC,
representing strong evidence of dwarf galaxy group infall. This procedure
depends on the gravitational pull of the LMC, thus allowing us to place a lower
bound on the Cloud's mass of . This
mass estimate is validated by applying the technique to a cosmological zoom-in
simulation of a Milky Way-like galaxy with an LMC analogue where we find that
while this lower bound may be overestimated, it will improve in the future with
smaller observational errors. We apply this technique to dwarf galaxies lacking
radial velocities and find that Eri 3 has a broad range of radial velocities
for which it has a significant chance () of having being bound to the
Cloud. We study the non-Magellanic classical satellites and find that Fornax
has an appreciable probability of being an LMC satellite if the LMC is
sufficiently massive. In addition, we explore how the orbits of the Milky Way
satellites change in the presence of the LMC and find a significant change for
several objects. Finally, we find that the LMC satellites are slightly smaller
than the Milky Way satellites at a fixed luminosity, possibly due to the
different tidal environments they have experienced.Comment: 9 pages, 7 figures. Submitted to MNRAS. Comments welcom
Nitrogen enrichment and clustered star formation at the dawn of the Galaxy
Anomalously high nitrogen-to-oxygen abundance ratios [N/O] are observed in
globular clusters (GCs), among the field stars of the Milky Way (MW), and even
in the gas in a galaxy. Using data from the APOGEE Data Release
17 and the Gaia Data Release 3, we present several independent lines of
evidence that most of the MW's high-[N/O] stars were born in situ in massive
bound clusters during the early, pre-disk evolution of the Galaxy.
Specifically, we show that distributions of metallicity [Fe/H], energy, the
angular momentum , and distance of the low-metallicity high-[N/O] stars
match the corresponding distributions of stars of the Aurora population and of
the in-situ GCs. We also show that the fraction of in-situ field high-[N/O]
stars, , increases rapidly with decreasing metallicity. During
epochs when metallicity evolves from to ,
the Galaxy spins up and transitions from a turbulent Aurora state to a
coherently rotating disk. This transformation is accompanied by many
qualitative changes. In particular, we show that high N/O abundances similar to
those observed in GN-z11 were common before the spin-up () when up to of the in-situ stars formed in massive
bound clusters. The dramatic drop of at
indicates that after the disk emerges the fraction of stars forming in massive
bound clusters decreases by two orders of magnitude.Comment: 18 pages, 13 figures, submitted to MNRA
Self-Organizing Maps. An application to the OGLE data and the Gaia Science Alerts
Self-Organizing Map (SOM) is a promising tool for exploring large
multi-dimensional data sets. It is quick and convenient to train in an
unsupervised fashion and, as an outcome, it produces natural clusters of data
patterns. An example of application of SOM to the new OGLE-III data set is
presented along with some preliminary results.
Once tested on OGLE data, the SOM technique will also be implemented within
the Gaia mission's photometry and spectrometry analysis, in particular, in
so-called classification-based Science Alerts. SOM will be used as a basis of
this system as the changes in brightness and spectral behaviour of a star can
be easily and quickly traced on a map trained in advance with simulated and/or
real data from other surveys.Comment: Presented as a poster at the "Classification and Discovery in Large
Astronomical Surveys" meeting, Ringberg Castle, 14-17 October, 200
Chemical and stellar properties of early-type dwarf galaxies around the Milky Way
Early-type dwarfs (ETDs) are the end points of the evolution of low-mass
galaxies whose gas supply has been extinguished. The cessation of
star-formation lays bare the ancient stellar populations. A wealth of
information is stored in the colours, magnitudes, metallicities and abundances
of resolved stars of the dwarf spheroidal and ultra-faint galaxies around the
Milky Way, allowing their chemistry and stellar populations to be studied in
great detail. Here, we summarize our current understanding, which has advanced
rapidly over the last decade thanks to the flourishing of large-scale
astrometric, photometric and spectroscopic surveys. We emphasise that the
primeval stellar populations in the ETDs provide a unique laboratory to study
the physical conditions on small scales at epochs beyond z=2. We highlight the
observed diversity of star-formation and chemical enrichment histories in
nearby dwarfs. These data can not yet be fully deciphered to reveal the key
processes in the dwarf evolution but the first successful attempts have been
made to pin down the sites of heavy element production.Comment: Invited Review published on August 1, 2022 in Nature Astronomy. The
Version of Record is available online at https://rdcu.be/cSPa
Inferred Evidence for Dark Matter Kinematic Substructure with SDSS–Gaia
We use the distribution of accreted stars in Sloan Digital Sky Survey–Gaia DR2 to demonstrate that a nontrivial fraction of the dark matter halo within galactocentric radii of 7.5–10 kpc and |z| > 2.5 kpc is in substructure and thus may not be in equilibrium. Using a mixture likelihood analysis, we separate the contributions of an old, isotropic stellar halo and a younger anisotropic population. The latter dominates and is uniform within the region studied. It can be explained as the tidal debris of a disrupted massive satellite on a highly radial orbit and is consistent with mounting evidence from recent studies. Simulations that track the tidal debris from such mergers find that the dark matter traces the kinematics of its stellar counterpart. If so, our results indicate that a component of the nearby dark matter halo that is sourced by luminous satellites is in kinematic substructure referred to as debris flow. These results challenge the Standard Halo Model, which is discrepant with the distribution recovered from the stellar data, and have important ramifications for the interpretation of direct detection experiments
Equilibrium models of the Milky Way mass are biased high by the LMC
Recent measurements suggest that the Large Magellanic Cloud (LMC) may weigh
as much as 25\% of the Milky Way. In this work we explore how such a large
satellite affects mass estimates of the Milky Way based on equilibrium
modelling of the stellar halo or other tracers. In particular, we show that if
the LMC is ignored, the Milky Way mass is overestimated by as much as 50\%.
This bias is due to the bulk motion in the outskirts of the Galaxy's halo and
can be, at least in part, accounted for with a simple modification to the
equilibrium modelling. Finally, we show that the LMC has a substantial effect
on the orbit Leo I which acts to increase its present day speed relative to the
Milky Way. We estimate that accounting for a LMC
would lower the inferred Milky Way mass to .Comment: 7 pages, 6 figures. Submitted to MNRAS. Comments welcom
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