35 research outputs found
Discovery of Extended Tidal Tails around the Globular Cluster Palomar 13
We use photometry from the DECam Legacy Survey to detect candidate tidal
tails extending ~5 deg on either side of the Palomar 13 globular cluster. The
tails are aligned with the proper motion of Palomar 13 and are consistent with
its old, metal-poor stellar population. We identify three RR Lyrae stars that
are plausibly associated with the tails, in addition to four previously known
in the cluster. From these RR Lyrae stars, we find that the mean distance to
the cluster and tails is kpc and estimate the total (initial)
luminosity of the cluster to be ,
consistent with previous claims that its initial luminosity was higher than its
current luminosity. Combined with previously-determined proper motion and
radial velocity measurements of the cluster, we find that Palomar 13 is on a
highly eccentric orbit () with a pericenter of ~9 kpc and an
apocenter of ~69 kpc, and a recent pericentric passage of the cluster ~75 Myr
ago. We note a prominent linear structure in the interstellar dust map that
runs parallel to the candidate tidal features, but conclude that reddening due
to dust is unlikely to account for the structure that we observe. If confirmed,
the Palomar 13 stellar stream would be one of very few streams with a known
progenitor system, making it uniquely powerful for studying the disruption of
globular clusters, the formation of the stellar halo, and the distribution of
matter within our Galaxy.Comment: 8 pages, 4 figures, 1 table. Submitted to AAS journal
Synthetic Gaia DR3 surveys from the FIRE cosmological simulations of Milky-Way-mass galaxies
The third data release (DR3) of Gaia has provided a five-fold increase in the
number of radial velocity measurements of stars, as well as a stark improvement
in parallax and proper motion measurements. To help with studies that seek to
test models and interpret Gaia DR3, we present nine Gaia synthetic surveys,
based on three solar positions in three Milky-Way-mass galaxies of the Latte
suite of the Fire-2 cosmological simulations. These synthetic surveys match the
selection function, radial velocity measurements, and photometry of Gaia DR3,
adapting the code base Ananke, previously used to match the Gaia DR2 release in
Sanderson et al. 2020. The synthetic surveys are publicly available and can be
found at http://ananke.hub.yt/. Similarly to the previous release of Ananke,
these surveys are based on cosmological simulations and thus able to model
non-equilibrium dynamical effects, making them a useful tool in testing and
interpreting Gaia DR3.Comment: 17 pages, 7 tables, 6 figure
Astrobites as a Community-led Model for Education, Science Communication, and Accessibility in Astrophysics
Support for early career astronomers who are just beginning to explore
astronomy research is imperative to increase retention of diverse practitioners
in the field. Since 2010, Astrobites has played an instrumental role in
engaging members of the community -- particularly undergraduate and graduate
students -- in research. In this white paper, the Astrobites collaboration
outlines our multi-faceted online education platform that both eases the
transition into astronomy research and promotes inclusive professional
development opportunities. We additionally offer recommendations for how the
astronomy community can reduce barriers to entry to astronomy research in the
coming decade
: Probing the Milky Way and Magellanic Clouds potentials with the 6-D map of the Orphan-Chenab stream
We present a 6-D map of the Orphan-Chenab (OC) stream by combining the data
from 5 years of Southern Stellar Stream Spectroscopic Survey observations
with Gaia EDR3 data. We reconstruct the proper motion, radial velocity,
distance and on-sky track of stream stars with spline models and extract the
stellar density along the stream. The stream has a total luminosity of
and an average metallicity of , similar to classical MW
satellites like Draco. The stream shows drastic changes in its physical width
varying from 200 pc to 1 kpc, a constant line of sight velocity dispersion of 5
km/s, but an increase in the velocity dispersion along the stream near
pericenter to 10 km/s. Despite the large apparent variation in the
stellar number density along the stream, the flow rate of stars along the
stream is remarkably constant. We model the 6-D stream track by a
Lagrange-point stripping method with a flexible MW potential in the presence of
a moving extended LMC potential. This allows us to constrain the mass profile
of the MW within the distance range 15.6 < r < 55.5 kpc, with the best measured
enclosed mass of within 32.4 kpc. With
the OC stream's closest approach distance to the LMC of kpc, our
stream measurements are highly sensitive to the LMC mass profile with the most
precise measurement of the LMC's enclosed mass being at 32.8 kpc with
. We confidently detect that the LMC
DM halo extends to at least 53 kpc. The fitting of the OC stream allows us to
constrain the past LMC trajectory and the degree of dynamical friction it
experienced. We demonstrate that the stars on the OC stream show large energy
and angular momentum spreads caused by the LMC perturbation and revealing the
limitations of orbital invariants for substructure identification in the MW
halo.Comment: submitted to MNRAS; comments welcome; data released with the paper is
available on Zenodo https://zenodo.org/record/722265
Broken into Pieces::ATLAS and Aliqa Uma as One Single Stream
We present the first spectroscopic measurements of the ATLAS and Aliqa Uma
streams from the Southern Stellar Stream Spectroscopic Survey (), in
combination with the photometric data from the Dark Energy Survey and
astrometric data from . From the coherence of spectroscopic members in
radial velocity and proper motion, we find out that these two systems are
extremely likely to be one stream with discontinuity in morphology and density
on the sky (the "kink" feature). We refer to this entire stream as the
ATLAS-Aliqa Uma stream, or the AAU stream. We perform a comprehensive
exploration of the effect of baryonic substructures and find that only an
encounter with the Sagittarius dwarf Gyr ago can create a feature
similar to the observed "kink". In addition, we also identify two gaps in the
ATLAS component associated with the broadening in the stream width (the
"broadening" feature). These gaps have likely been created by small mass
perturbers, such as dark matter halos, as the AAU stream is the most distant
cold stream known with severe variations in both the stream surface density and
the stream track on the sky. With the stream track, stream distance and
kinematic information, we determine the orbit of the AAU stream and find that
it has been affected by the Large Magellanic Cloud, resulting in a misalignment
between the proper motion and stream track. Together with the Orphan-Chenab
Stream, AAU is the second stream pair that has been found to be a single stream
separated into two segments by external perturbation.Comment: 33 pages, 22 figures (including 1 movie), 3 tables. Accepted for
publication in Ap
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Discovery and Modeling of Milky Way Stellar Streams
Stellar streams, the tidal remnants of accreted globular clusters and dwarf galaxies, are uniquely powerful tools for studying the Milky Way. In particular, they allow for strong constraints on the local distribution of dark matter, and they provide insight into how our Galaxy has evolved over time. Models of stellar streams enable measurements of the overall shape and mass of the Milky Way’s halo, which is sensitive to dark matter and galaxy formation physics. On smaller scales, stellar streams are one of the most promising methods for detecting the presence of small clumps of dark matter, which will allow for unprecedented constraints on the nature of the dark matter particle. Streams also provide important constraints on the formation of the Milky Way stellar halo and the history of hierarchical structure formation in our Galaxy, as predicted by the standard Lambda Cold Dark Matter (LCDM) cosmological model.
These studies require a large, well-observed sample of stellar streams with full 6D position and velocity measurements. Until recently, such a population was unattainable, but with the advent of large surveys, observations of stellar streams have improved significantly in recent years. In this thesis, I present my work on assembling and modeling the first such population of stellar streams in 6D.
First, I present the discovery of a large sample of stellar streams in the Dark Energy Survey, which increased the known population of streams by ~50%, as well as the discovery of a unique stellar stream associated with the Palomar 13 globular cluster. I then describe the measurement of the velocities of this new sample of stellar streams via spectroscopic survey and with data from the Gaia satellite, and present results of modeling this population of stellar streams to constrain the distribution of matter in our Galaxy, including the mass of the Milky Way’s largest satellite, the Large Magellanic Cloud. Finally, I conclude and discuss future efforts in the study of near-field cosmology with this population of 6D stellar streams
BoletÃn oficial de la provincia de Santander: Número 1 - 1887 Julio 01
We perform a search for stellar streams around the Milky Way using the first 3 yr of multiband optical imaging data from the Dark Energy Survey (DES). We use DES data covering ∼5000 deg2 to a depth of g>23.5 with a relative photometric calibration uncertainty of <1%. This data set yields unprecedented sensitivity to the stellar density field in the southern celestial hemisphere, enabling the detection of faint stellar streams to a heliocentric distance of ∼50 kpc. We search for stellar streams using a matched filter in color–magnitude space derived from a synthetic isochrone of an old, metal-poor stellar population. Our detection technique recovers four previously known thin stellar streams: Phoenix, ATLAS, Tucana III, and a possible extension of Molonglo. In addition, we report the discovery of 11 new stellar streams. In general, the new streams detected by DES are fainter, more distant, and lower surface brightness than streams detected by similar techniques in previous photometric surveys. As a by-product of our stellar stream search, we find evidence for extratidal stellar structure associated with four globular clusters: NGC 288, NGC 1261, NGC 1851, and NGC 1904. The ever-growing sample of stellar streams will provide insight into the formation of the Galactic stellar halo, the Milky Way gravitational potential, and the large- and small-scale distribution of dark matter around the Milky Way
Synthetic Gaia DR3 Surveys from the FIRE Cosmological Simulations of Milky Way-mass Galaxies
The third data release (DR3) of Gaia has provided a fivefold increase in the number of radial velocity measurements of stars, as well as a stark improvement in parallax and proper motion measurements. To help with studies that seek to test models and interpret Gaia DR3, we present nine Gaia synthetic surveys, based on three solar positions in three Milky Way-mass galaxies of the Latte suite of the Fire -2 cosmological simulations. These synthetic surveys match the selection function, radial velocity measurements, and photometry of Gaia DR3, adapting the code base Ananke , previously used to match the Gaia DR2 release by Sanderson et al. The synthetic surveys are publicly available and can be found at http://ananke.hub.yt/ . Similarly to the previous release of Ananke , these surveys are based on cosmological simulations and thus are able to model nonequilibrium dynamical effects, making them a useful tool in testing and interpreting Gaia DR3
Signatures of Tidal Disruption of the Hercules Ultrafaint Dwarf Galaxy
The Hercules ultrafaint dwarf galaxy (UFD) has long been hypothesized to be tidally disrupting, yet no conclusive evidence has been found for tidal disruption owing partly to difficulties in identifying Hercules member stars. In this work, we present a homogeneous reanalysis of new and existing observations of Hercules, including the detection of a new potential member star located ∼1° (∼1.7 kpc) west of the center of the system. In addition to measuring the line-of-sight velocity gradient, we compare predictions from dynamical models of stream formation to these observations. We report an updated velocity dispersion measurement based on 28 stars, km s ^−1 , which is significantly lower than previous measurements. We find that the line-of-sight velocity gradient is km s ^−1 kpc along the major axis of Hercules, consistent with zero within 1 σ . Our dynamical models of stream formation, on the other hand, can reproduce the morphology of the Hercules UFD, specifically the misalignment between the elongation and the orbital motion direction. Additionally, these dynamical models indicate that any radial velocity gradient from tidal disruption would be too small, km s ^−1 kpc, to be detectable with current sample sizes. Combined with our analysis of the tidal radius evolution of the system as a function of its orbital phase, we argue that it is likely that Hercules is indeed currently undergoing tidal disruption in its extended stellar halo with a line-of-sight velocity gradient too small to be detected with current observational data sets
Lipidome profiling with Raman microspectroscopy identifies macrophage response to surface topographies of implant materials
Biomaterial characteristics such as surface topographies have been shown to modulate macrophage phenotypes. The standard methodologies to measure macrophage response to biomaterials are marker-based and invasive. Raman microspectroscopy (RM) is a marker-independent, noninvasive technology that allows the analysis of living cells without the need for staining or processing. In the present study, we analyzed human monocyte-derived macrophages (MDMs) using RM, revealing that macrophage activation by lipopolysaccharides (LPS), interferons (IFN), or cytokines can be identified by lipid composition, which significantly differs in M0 (resting), M1 (IFN-γ/LPS), M2a (IL-4/IL-13), and M2c (IL-10) MDMs. To identify the impact of a biomaterial on MDM phenotype and polarization, we cultured macrophages on titanium disks with varying surface topographies and analyzed the adherent MDMs with RM. We detected surface topography–induced changes in MDM biochemistry and lipid composition that were not shown by less sensitive standard methods such as cytokine expression or surface antigen analysis. Our data suggest that RM may enable a more precise classification of macrophage activation and biomaterial–macrophage interaction