634 research outputs found
An HST/ACS View of the Inhomogeneous Outer Halo of M31
We present a high precision photometric view of the stellar populations in
the outer halo of M31, using data taken with the Hubble Space Telescope
Advanced Camera for Surveys (HST/ACS). We analyse the field populations
adjacent to 11 luminous globular clusters which sample the galactocentric
radial range 18 < R < 100 kpc and reach a photometric depth of ~2.5 magnitudes
below the horizontal branch (m_F814W ~27 mag). The colour-magnitude diagrams
(CMDs) are well populated out to ~60 kpc and exhibit relatively metal-rich red
giant branches, with the densest fields also showing evidence for prominent red
clumps. We use the Dartmouth isochrones to construct metallicity distribution
functions (MDFs) which confirm the presence of dominant populations with
= -0.6 to -1.0 dex and considerable metallicity dispersions of 0.2 to
0.3 dex (assuming a 10 Gyr population and scaled-Solar abundances). The average
metallicity over the range 30 - 60 kpc is [Fe/H] = -0.8 +/- 0.14 dex, with no
evidence for a significant radial gradient. Metal-poor stars ([Fe/H] <= -1.3)
typically account for < 10-20 % of the population in each field, irrespective
of radius. Assuming our fields are unbiased probes of the dominant stellar
populations in these parts, we find that the M31 outer halo remains
considerably more metal-rich than that of the Milky Way out to at least 60 kpc.Comment: Accepted for publication in MNRAS. 10 pages, 6 figure
Major Substructure in the M31 Outer Halo: the South-West Cloud
We undertake the first detailed analysis of the stellar population and
spatial properties of a diffuse substructure in the outer halo of M31. The
South-West Cloud lies at a projected distance of ~100 kpc from the centre of
M31, and extends for at least ~50 kpc in projection. We use Pan-Andromeda
Archaeological Survey photometry of red giant branch stars to determine a
distance to the South-West Cloud of 793 +/- 45 kpc. The metallicity of the
cloud is found to be [Fe/H] = -1.3 +/- 0.1. This is consistent with the
coincident globular clusters PAndAS-7 and PAndAS-8, which have metallicities
determined using an independent technique of [Fe/H] = -1.35 +/- 0.15. We
measure a brightness for the Cloud of M_V = -12.1 mag; this is ~75 per cent of
the luminosity implied by the luminosity-metallicity relation. Under the
assumption that the South-West Cloud is the visible remnant of an accreted
dwarf satellite, this suggests that the progenitor object was amongst M31's
brightest dwarf galaxies prior to disruption.Comment: 13 pages, 9 figures, accepted for publication in MNRA
Small representations of finite classical groups
Finite group theorists have established many formulas that express
interesting properties of a finite group in terms of sums of characters of the
group. An obstacle to applying these formulas is lack of control over the
dimensions of representations of the group. In particular, the representations
of small dimensions tend to contribute the largest terms to these sums, so a
systematic knowledge of these small representations could lead to proofs of
important conjectures which are currently out of reach. Despite the
classification by Lusztig of the irreducible representations of finite groups
of Lie type, it seems that this aspect remains obscure. In this note we develop
a language which seems to be adequate for the description of the "small"
representations of finite classical groups and puts in the forefront the notion
of rank of a representation. We describe a method, the "eta correspondence", to
construct small representations, and we conjecture that our construction is
exhaustive. We also give a strong estimate on the dimension of small
representations in terms of their rank. For the sake of clarity, in this note
we describe in detail only the case of the finite symplectic groups.Comment: 18 pages, 9 figures, accepted for publications in the proceedings of
the conference on the occasion of Roger Howe's 70th birthday (1-5 June 2015,
Yale University, New Haven, CT
The outer halo globular cluster system of M31 - II. Kinematics
We present a detailed kinematic analysis of the outer halo globular cluster
(GC) system of M31. Our basis for this is a set of new spectroscopic
observations for 78 clusters lying at projected distances between Rproj ~20-140
kpc from the M31 centre. These are largely drawn from the recent PAndAS
globular cluster catalogue; 63 of our targets have no previous velocity data.
Via a Bayesian maximum likelihood analysis we find that GCs with Rproj > 30 kpc
exhibit coherent rotation around the minor optical axis of M31, in the same
direction as more centrally- located GCs, but with a smaller amplitude of
86+/-17 km s-1. There is also evidence that the velocity dispersion of the
outer halo GC system decreases as a function of projected distance from the M31
centre, and that this relation can be well described by a power law of index ~
-0.5. The velocity dispersion profile of the outer halo GCs is quite similar to
that of the halo stars, at least out to the radius up to which there is
available information on the stellar kinematics. We detect and discuss various
velocity correlations amongst subgroups of GCs that lie on stellar debris
streams in the M31 halo. Many of these subgroups are dynamically cold,
exhibiting internal velocity dispersions consistent with zero. Simple Monte
Carlo experiments imply that such configurations are unlikely to form by
chance, adding weight to the notion that a significant fraction of the outer
halo GCs in M31 have been accreted alongside their parent dwarf galaxies. We
also estimate the M31 mass within 200 kpc via the Tracer Mass Estimator,
finding (1.2 - 1.6) +/- 0.2 10^{12}M_sun. This quantity is subject to
additional systematic effects due to various limitations of the data, and
assumptions built in into the TME. Finally, we discuss our results in the
context of formation scenarios for the M31 halo.Comment: 24 pages, 12 figures, 7 tables; Accepted for publication in MNRA
1000 Norms Project: Protocol of a cross-sectional study cataloging human variation
Background Clinical decision-making regarding diagnosis and management largely depends on comparison with healthy or ‘normal’ values. Physiotherapists and researchers therefore need access to robust patient-centred outcome measures and appropriate reference values. However there is a lack of high-quality reference data for many clinical measures. The aim of the 1000 Norms Project is to generate a freely accessible database of musculoskeletal and neurological reference values representative of the healthy population across the lifespan. Methods/design In 2012 the 1000 Norms Project Consortium defined the concept of ‘normal’, established a sampling strategy and selected measures based on clinical significance, psychometric properties and the need for reference data. Musculoskeletal and neurological items tapping the constructs of dexterity, balance, ambulation, joint range of motion, strength and power, endurance and motor planning will be collected in this cross-sectional study. Standardised questionnaires will evaluate quality of life, physical activity, and musculoskeletal health. Saliva DNA will be analysed for the ACTN3 genotype (‘gene for speed’). A volunteer cohort of 1000 participants aged 3 to 100 years will be recruited according to a set of self-reported health criteria. Descriptive statistics will be generated, creating tables of mean values and standard deviations stratified for age and gender. Quantile regression equations will be used to generate age charts and age-specific centile values. Discussion This project will be a powerful resource to assist physiotherapists and clinicians across all areas of healthcare to diagnose pathology, track disease progression and evaluate treatment response. This reference dataset will also contribute to the development of robust patient-centred clinical trial outcome measures
AN ULTRA-FAINT GALAXY CANDIDATE DISCOVERED in EARLY DATA from the MAGELLANIC SATELLITES SURVEY
We report a new ultra-faint stellar system found in Dark Energy Camera data from the first observing run of the Magellanic Satellites Survey (MagLiteS). MagLiteS J0644-5953 (Pictor II or Pic II) is a low surface brightness (μ = 28.5+1 -1 mag arcsec-2 within its half-light radius) resolved overdensity of old and metal-poor stars located at a heliocentric distance of 45+5 -4 kpc. The physical size (r1/2 = 46+15 -11) and low luminosity (Mv = -3.2+0.4 -0.5 mag) of this satellite are consistent with the locus of spectroscopically confirmed ultra-faint galaxies. MagLiteS J0644-5953 (Pic II) is located 11.3+3.1 -0.9 kpc from the Large Magellanic Cloud (LMC), and comparisons with simulation results in the literature suggest that this satellite was likely accreted with the LMC. The close proximity of MagLiteS J0644-5953 (Pic II) to the LMC also makes it the most likely ultra-faint galaxy candidate to still be gravitationally bound to the LMC.Peer reviewe
Deep Gemini/GMOS imaging of an extremely isolated globular cluster in the Local Group
We report on deep imaging of a remote M31 globular cluster, MGC1, obtained
with Gemini/GMOS. Our colour-magnitude diagram for this object extends ~5
magnitudes below the tip of the red giant branch and exhibits features
consistent with an ancient metal-poor stellar population, including a long,
well-populated horizontal branch. The red giant branch locus suggests MGC1 has
a metal abundance [M/H] ~ -2.3. We measure the distance to MGC1 and find that
it lies ~160 kpc in front of M31 with a distance modulus of 23.95 +/- 0.06.
Combined with its large projected separation of 117 kpc from M31 this implies a
deprojected radius of Rgc = 200 +/- 20 kpc, rendering it the most isolated
known globular cluster in the Local Group by some considerable margin. We
construct a radial brightness profile for MGC1 and show that it is both
centrally compact and rather luminous, with Mv = -9.2. Remarkably, the cluster
profile shows no evidence for a tidal limit and we are able to trace it to a
radius of at least 450 pc, and possibly as far as ~900 pc. The profile exhibits
a power-law fall-off with exponent -2.5, breaking to -3.5 in its outermost
parts. This core-halo structure is broadly consistent with expectations derived
from numerical models, and suggests that MGC1 has spent many gigayears in
isolation.Comment: Accepted for publication in MNRA
Prevalence, Clinical Profile, and Significance of Left Ventricular Remodeling in the End-Stage Phase of Hypertrophic Cardiomyopathy
Background—
End stage (ES) is a recognized part of the hypertrophic cardiomyopathy (HCM) disease spectrum. Frequency, clinical profile and course, and treatment strategies in these patients remain incompletely defined.
Methods and Results—
Three HCM cohorts comprised 1259 patients, including 44 (3.5%) characterized as ES with systolic dysfunction (ejection fraction <50% at rest; range 15% to 49%). ES developed at a wide age range (14 to 74 years), with 45% of patients ≤40 years old. Although 29 patients (66%) died of progressive heart failure, had sudden death events, or underwent heart transplantation, 15 (34%) survived with medical management over 3±3 years. Duration from onset of HCM symptoms to ES identification was considerable (14±10 years), but ES onset to death/transplantation was brief (2.7±2 years). ES occurred with similar frequency in patients with or without prior myectomy (
P
=0.84). Appropriate defibrillator interventions were 10% per year in patients awaiting donor hearts. Most ES patients (n=23; 52%) showed substantial left ventricular (LV) remodeling with cavity dilatation. Less complete remodeling occurred in 21 patients (48%), including 5 with persistence of a nondilated and markedly hypertrophied LV. Pathology and magnetic resonance imaging showed extensive (transmural) fibrosis in 9 of 11 ES patients. At initial evaluation, patients who developed ES were younger with more severe symptoms, had a larger LV cavity, and more frequently had a family history of ES than other HCM patients.
Conclusions—
ES of nonobstructive HCM has an expanded and more diverse clinical expression than previously appreciated, including occurrence in young patients, heterogeneous patterns of remodeling, frequent association with atrial fibrillation, and impaired LV contractility that precedes cavity dilatation, wall thinning, and heart failure symptoms. ES is an unfavorable complication (mortality rate 11% per year) and a sudden death risk factor; it requires vigilance to permit timely recognition and the necessity for defibrillator implantation and heart transplantation
A Keck/DEIMOS spectroscopic survey of the faint M31 satellites And IX, And XI, And XII, and And XIII
We present the first spectroscopic analysis of the faint M31 satellite
galaxies, AndXI and AndXIII, and a reanalysis of existing spectroscopic data
for two further faint companions, And IX and AndXII. By combining data obtained
using the DEIMOS spectrograph mounted on the Keck II telescope with deep
photometry from the Suprime-Cam instrument on Subaru, we have calculated global
properties for the dwarfs, such as systemic velocities, metallicites and
half-light radii.We find each dwarf to be very metal poor ([Fe/H] -2 both
photometrically and spectroscopically, from their stacked spectrum), and as
such, they continue to follow the luminosity-metallicity relationship
established with brighter dwarfs. We are unable to resolve a dispersion for And
XI due to small sample size and low S/N, but we set a one sigma upper limit of
sigma-v <5 km/s. For And IX, And XII and And XIII we resolve velocity
dispersions of v=4.5 (+3.4,-3.2), 2.6(+5.1,-2.6) and 9.7(+8.9,-4.5) km/s, and
derive masses within the half light radii of 6.2(+5.3,-5.1)x10^6 Msun, 2.4
(+6.5,-2.4)x10^6 Msun and 1.1(+1.4,-0.7)x10^7 Msun respectively. We discuss
each satellite in the context of the Mateo relations for dwarf spheroidal
galaxies, and the Universal halo profiles established for Milky Way dwarfs
(Walker et al. 2009). For both galaxies, this sees them fall below the
Universal halo profiles of Walker et al. (2009). When combined with the
findings of McConnachie & Irwin (2006a), which reveal that the M31 satellites
are twice as extended (in terms of both half-light and tidal radii) as their
Milky Way counterparts, these results suggest that the satellite population of
the Andromeda system could inhabit halos that are significantly different from
those of the Milky Way in terms of their central densities (abridged).Comment: 26 pages, 18 figures, MNRAS submitte
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