3,437 research outputs found
The Observational and Theoretical Tidal Radii of Globular Clusters in M87
Globular clusters have linear sizes (tidal radii) which theory tells us are
determined by their masses and by the gravitational potential of their host
galaxy. To explore the relationship between observed and expected radii, we
utilize the globular cluster population of the Virgo giant M87. Unusually deep,
high signal-to-noise images of M87 are used to measure the effective and
limiting radii of approximately 2000 globular clusters. To compare with these
observations, we simulate a globular cluster population that has the same
characteristics as the observed M87 cluster population. Placing these simulated
clusters in the well-studied tidal field of M87, the orbit of each cluster is
solved and the theoretical tidal radius of each cluster is determined. We
compare the predicted relationship between cluster size and projected
galactocentric distance to observations. We find that for an isotropic
distribution of cluster velocities, theoretical tidal radii are approximately
equal to observed limiting radii for Rgc < 10 kpc. However, the isotropic
simulation predicts a steep increase in cluster size at larger radii, which is
not observed in large galaxies beyond the Milky Way. To minimize the
discrepancy between theory and observations, we explore the effects of orbital
anisotropy on cluster sizes, and suggest a possible orbital anisotropy profile
for M87 which yields a better match between theory and observations. Finally,
we suggest future studies which will establish a stronger link between
theoretical tidal radii and observed radii.Comment: 8 pages, 8 figures, Accepted for publication in Ap
Globular Cluster Scale Sizes in Giant Galaxies: Orbital Anisotropy and Tidally Under-filling Clusters in M87, NGC 1399, and NGC 5128
We investigate the shallow increase in globular cluster half-light radii with
projected galactocentric distance observed in the giant galaxies M87,
NGC 1399, and NGC 5128. To model the trend in each galaxy, we explore the
effects of orbital anisotropy and tidally under-filling clusters. While a
strong degeneracy exists between the two parameters, we use kinematic studies
to help constrain the distance beyond which cluster orbits become
anisotropic, as well as the distance beyond which clusters are
tidally under-filling. For M87 we find kpc and kpc and kpc.
The connection of with each galaxy's mass profile indicates the
relationship between size and may be imposed at formation, with only
inner clusters being tidally affected. The best fitted models suggest the
dynamical histories of brightest cluster galaxies yield similar present-day
distributions of cluster properties. For NGC 5128, the central giant in a small
galaxy group, we find kpc and kpc. While we
cannot rule out a dependence on , NGC 5128 is well fitted by a tidally
filling cluster population with an isotropic distribution of orbits, suggesting
it may have formed via an initial fast accretion phase. Perturbations from the
surrounding environment may also affect a galaxy's orbital anisotropy profile,
as outer clusters in M87 and NGC 1399 have primarily radial orbits while outer
NGC 5128 clusters remain isotropic.Comment: 16 pages, 7 figures, 4 tables, Accepted for publication in MNRA
Stable isotope evidence for Amerindian subsistence in Newfoundland, 2800 B.C. to A.D. 1829
Archaeological research has informed on the lifeways of Newfoundland’s past
Amerindian populations, but their subsistence practices are still poorly understood,
particular with respect to the roles played by marine and terrestrial resources. To
investigate Amerindian diet, isotope ratios (δ¹³Ccoll, δ¹⁵Ncoll) were measured in 86
skeletons from the Maritime Archaic site of Port au Choix-3 (4500 – 4000 cal B.P.), and
in 29 skeletons from 12 Recent Indian/Beothuk sites (AD 1000 – 1800). Whole dietary
carbon was estimated by measuring carbon isotopes in the enamel of 12 Beothuk
skeletons. The Maritime Archaic sample was characterized by the presence of at least two
subsistence patterns: one marine-based, and the other mixed marine-terrestrial. These
patterns may relate to geographic origin, or to biosocial categories. Recent
Indian/Beothuk diet was revealed to be predominantly mixed marine-terrestrial in origin,
but characterized by increasing amounts of terrestrial foods in the late historic period
ARIBA: rapid antimicrobial resistance genotyping directly from sequencing reads.
Antimicrobial resistance (AMR) is one of the major threats to human and animal health worldwide, yet few high-throughput tools exist to analyse and predict the resistance of a bacterial isolate from sequencing data. Here we present a new tool, ARIBA, that identifies AMR-associated genes and single nucleotide polymorphisms directly from short reads, and generates detailed and customizable output. The accuracy and advantages of ARIBA over other tools are demonstrated on three datasets from Gram-positive and Gram-negative bacteria, with ARIBA outperforming existing methods
Neurobiologic Features of Fibromyalgia Are Also Present Among Rheumatoid Arthritis Patients
Funding: The study recieved support from Pfizer. The funder had no role in study design, data collection, analysis, decision to publish or preparation of the manuscript. The content is solely the responsibility of the authors. Funding Information Pfizer Aptinyx Cerephex ACKNOWLEDGEMENTS: The authors wish to thank all of the patient volunteers. We also thank Mariella D’Allesandro for supporting recruitment and data collection.Peer reviewedPostprin
The epigenetic clock is correlated with physical and cognitive fitness in the Lothian Birth Cohort 1936
Background: The DNA methylation-based 'epigenetic clock' correlates strongly with chronological age, but it is currently unclear what drives individual differences. We examine cross-sectional and longitudinal associations between the epigenetic clock and four mortality-linked markers of physical and mental fitness: lung function, walking speed, grip strength and cognitive ability. Methods: DNA methylation-based age acceleration (residuals of the epigenetic clock estimate regressed on chronological age) were estimated in the Lothian Birth Cohort 1936 at ages 70 (n=920), 73 (n=299) and 76 (n=273) years. General cognitive ability, walking speed, lung function and grip strength were measured concurrently. Cross-sectional correlations between age acceleration and the fitness variables were calculated. Longitudinal change in the epigenetic clock estimates and the fitness variables were assessed via linear mixed models and latent growth curves. Epigenetic age acceleration at age 70 was used as a predictor of longitudinal change in fitness. Epigenome-wide association studies (EWASs) were conducted on the four fitness measures. Results: Cross-sectional correlations were significant between greater age acceleration and poorer performance on the lung function, cognition and grip strength measures (r range: -0.07 to -0.05, P range: 9.7 x 10 to 0.024). All of the fitness variables declined over time but age acceleration did not correlate with subsequent change over 6 years. There were no EWAS hits for the fitness traits. Conclusions: Markers of physical and mental fitness are associated with the epigenetic clock (lower abilities associated with age acceleration). However, age acceleration does not associate with decline in these measures, at least over a relatively short follow-up
Molecular Tracers of the Central 12 pc of the Galactic Center
We have used the BIMA array to image the Galactic Center with a 19-pointing
mosaic in HCN(1-0), HCO+(1-0), and H 42-alpha emission with 5 km/s velocity
resolution and 13'' x 4'' angular resolution. The 5' field includes the
circumnuclear ring (CND) and parts of the 20 and 50 km/s clouds. HCN(1-0) and
HCO+ trace the CND and nearby giant molecular clouds while the H 42-alpha
emission traces the ionized gas in Sgr A West. We find that the CND has a
definite outer edge in HCN and HCO+ emission at ~45'' radius and appears to be
composed of two or three distinct streams of molecular gas rotating around the
nucleus. Outside the CND, HCN and HCO+ trace dense clumps of high-velocity gas
in addition to optically thick emission from the 20 and 50 km/s clouds. A
molecular ridge of compressed gas and dust, traced in NH3 emission and
self-absorbed HCN and HCO+, wraps around the eastern edge of Sgr A East. Just
inside this ridge are several arcs of gas which have been accelerated by the
impact of Sgr A East with the 50 km/s cloud. HCN and HCO+ emission trace the
extension of the northern arm of Sgr A West which appears to be an independent
stream of neutral and ionized gas and dust originating outside the CND. Broad
line widths and OH maser emission mark the intersection of the northern arm and
the CND. Comparison to previous NH3 and 1.2mm dust observations shows that HCN
and HCO+ preferentially trace the CND and are weaker tracers of the GMCs than
NH3 and dust. We discuss possible scenarios for the emission mechanisms and
environment at the Galactic center which could explain the differences in these
images.Comment: 24 pages, including 17 figures; to appear in The Astrophysical
Journa
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