91 research outputs found
A Deeper Look at Leo IV: Star Formation History and Extended Structure
We present MMT/Megacam imaging of the Leo~IV dwarf galaxy in order to
investigate its structure and star formation history, and to search for signs
of association with the recently discovered Leo~V satellite. Based on
parameterized fits, we find that Leo~IV is round, with (at
the 68\% confidence limit) and a half-light radius of pc.
Additionally, we perform a thorough search for extended structures in the plane
of the sky and along the line of sight. We derive our surface brightness
detection limit by implanting fake structures into our catalog with stellar
populations identical to that of Leo~IV. We show that we are sensitive to
stream-like structures with surface brightness mag
arcsec, and at this limit, we find no stellar bridge between Leo IV (out
to a radius of 0.5 kpc) and the recently discovered, nearby satellite Leo
V. Using the color magnitude fitting package StarFISH, we determine that Leo~IV
is consistent with a single age (14 Gyr), single metallicity
() stellar population, although we can not rule out a
significant spread in these value. We derive a luminosity of
. Studying both the spatial distribution and frequency of
Leo~IV's 'blue plume' stars reveals evidence for a young (2 Gyr) stellar
population which makes up 2\% of its stellar mass. This sprinkling of
star formation, only detectable in this deep study, highlights the need for
further imaging of the new Milky Way satellites along with theoretical work on
the expected, detailed properties of these possible 'reionization fossils'.Comment: 26 pages, 14 figures, emulateapj format, ApJ accepted versio
The ACS Fornax Cluster Survey. VI. The Nuclei of Early-Type Galaxies in the Fornax Cluster
The Advanced Camera for Surveys (ACS) Fornax Cluster Survey is a Hubble Space
Telescope program to image 43 early-type galaxies in the Fornax cluster, using
the F475W and F850LP bandpasses of the ACS. We employ both 1D and 2D techniques
to characterize the properties of the stellar nuclei in these galaxies, defined
as the central "luminosity excesses" relative to a Sersic model fitted to the
underlying host. We find 72+/-13% of our sample (31 galaxies) to be nucleated,
with only three of the nuclei offset by more than 0.5" from their galaxy
photocenter, and with the majority of nuclei having colors bluer than their
hosts. The nuclei are observed to be larger, and brighter, than typical Fornax
globular clusters, and to follow different structural scaling relations. A
comparison of our results to those from the ACS Virgo Cluster Survey reveals
striking similarities in the properties of the nuclei belonging to these
different environments. We briefly review a variety of proposed formation
models and conclude that, for the low-mass galaxies in our sample, the most
important mechanism for nucleus growth is probably infall of star clusters
through dynamical friction, while for higher mass galaxies, gas accretion
triggered by mergers, accretions and tidal torques is likely to dominate, with
the relative importance of these two processes varying smoothly as a function
of galaxy mass. Some intermediate-mass galaxies in our sample show a complexity
in their inner structure that may be the signature of "hybrid nuclei" that
arose through parallel formation channels.Comment: 34 pages, 27 figures, accepted for publication in ApJ
The Star Formation History and Extended Structure of the Hercules Milky Way Satellite
We present imaging of the recently discovered Hercules Milky Way satellite
and its surrounding regions to study its structure, star formation history and
to thoroughly search for signs of disruption. We robustly determine the
distance, luminosity, size and morphology of Hercules utilizing a bootstrap
approach to characterize our uncertainties. We derive a distance to Hercules of
kpc via a comparison to empirical and theoretical isochrones. As
previous studies have found, Hercules is very elongated, with
and a half light radius of pc. Using
the color magnitude fitting package StarFISH, we determine that Hercules is old
( Gyr) and metal poor (), with a spread in metallicity, in
agreement with previous spectroscopic work. We infer a total absolute magnitude
of . Our innovative search for external Hercules structure both
in the plane of the sky and along the line of sight yields some evidence that
Hercules is embedded in a larger stream of stars. A clear stellar extension is
seen to the Northwest with several additional candidate stellar overdensities
along the position angle of Hercules out to 35' (1.3 kpc). While
the association of any of the individual stellar overdensities with Hercules is
difficult to determine, we do show that the summed color magnitude diagram of
all three is consistent with Hercules' stellar population. Finally, we estimate
that any change in the distance to Hercules across its face is at most 6
kpc; and the data are consistent with Hercules being at the same distance
throughout.Comment: 50 pages, 15 figures, submitted to the Astrophysical Journa
Theoretical Overview: The New Mesons
After commenting on the state of contemporary hadronic physics and
spectroscopy, I highlight four areas where the action is: searching for the
relevant degrees of freedom, mesons with beauty and charm, chiral symmetry and
the D_{sJ} levels, and X(3872) and the lost tribes of charmonium.Comment: 10 pages, uses jpconf.cls; talk at First Meeting of the APS Topical
Group on Hadronic Physic
Swordtail Fry Attend to Chemical and Visual Cues in Detecting Predators and Conspecifics
Predation pressure and energy requirements present particularly salient opposing selective pressures on young fish. Thus, fry are expected to possess sophisticated means of detecting predators and resources. Here we tested the hypotheses that fry of the swordtail fish Xiphophorus birchmanni use chemical and visual cues in detection of predators and conspecifics. To test these hypotheses we presented young (<7 day-old) fry with combinations of visual and chemical stimuli from adult conspecifics and predators. We found that exposure to predator odors resulted in shoal tightening similar to that observed when fry were presented with visual cues alone. In trials with conspecific stimuli, fry were particularly attracted to adult conspecifics when presented simultaneous visual and chemical stimuli compared to the visual stimulus alone. These results show that fry attend to the odors of adult conspecifics, whose presence in a particular area may signal the location of resources as well as an absence of predators. This is one of the first studies to show that such young fish use chemical and visual cues in predator detection and in interactions with conspecifics. Previous research in X. birchmanni has shown that anthropogenic alteration of the chemical environment disrupts intraspecific chemical communication among adults; we suggest that because fry use the same chemosensory pathways to detect predators and conspecifics, alteration of the chemical environment may critically disrupt predator and resource detection
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International meta-analysis of PTSD genome-wide association studies identifies sex- and ancestry-specific genetic risk loci.
The risk of posttraumatic stress disorder (PTSD) following trauma is heritable, but robust common variants have yet to be identified. In a multi-ethnic cohort including over 30,000 PTSD cases and 170,000 controls we conduct a genome-wide association study of PTSD. We demonstrate SNP-based heritability estimates of 5-20%, varying by sex. Three genome-wide significant loci are identified, 2 in European and 1 in African-ancestry analyses. Analyses stratified by sex implicate 3 additional loci in men. Along with other novel genes and non-coding RNAs, a Parkinson's disease gene involved in dopamine regulation, PARK2, is associated with PTSD. Finally, we demonstrate that polygenic risk for PTSD is significantly predictive of re-experiencing symptoms in the Million Veteran Program dataset, although specific loci did not replicate. These results demonstrate the role of genetic variation in the biology of risk for PTSD and highlight the necessity of conducting sex-stratified analyses and expanding GWAS beyond European ancestry populations
Age-dependent white matter disruptions after military traumatic brain injury: Multivariate analysis results from ENIGMA brain injury
Mild Traumatic brain injury (mTBI) is a signature wound in military personnel, and repetitive mTBI has been linked to age-related neurogenerative disorders that affect white matter (WM) in the brain. However, findings of injury to specific WM tracts have been variable and inconsistent. This may be due to the heterogeneity of mechanisms, etiology, and comorbid disorders related to mTBI. Non-negative matrix factorization (NMF) is a data-driven approach that detects covarying patterns (components) within high-dimensional data. We applied NMF to diffusion imaging data from military Veterans with and without a self-reported TBI history. NMF identified 12 independent components derived from fractional anisotropy (FA) in a large dataset (n = 1,475) gathered through the ENIGMA (Enhancing Neuroimaging Genetics through Meta-Analysis) Military Brain Injury working group. Regressions were used to examine TBI- and mTBI-related associations in NMF-derived components while adjusting for age, sex, post-traumatic stress disorder, depression, and data acquisition site/scanner. We found significantly stronger age-dependent effects of lower FA in Veterans with TBI than Veterans without in four components (q \u3c 0.05), which are spatially unconstrained by traditionally defined WM tracts. One component, occupying the most peripheral location, exhibited significantly stronger age-dependent differences in Veterans with mTBI. We found NMF to be powerful and effective in detecting covarying patterns of FA associated with mTBI by applying standard parametric regression modeling. Our results highlight patterns of WM alteration that are differentially affected by TBI and mTBI in younger compared to older military Veterans
Combination leflunomide and methotrexate (MTX) therapy for patients with active rheumatoid arthritis failing MTX monotherapy: open-label extension of a randomized, double-blind, placebo controlled trial
P e r s o n a l n o n -c o m m e r c i a l u s e o n l y . T h e J o u r n a l o f R h e u m a t o l o g y . C o p y r i g h t © 2 0 0 4 . A l l r i g h t s r e s e r v e d Conclusion. Response to therapy was maintained to 48 weeks of treatment in patients who continued to receive LEF and MTX during the extension. Importantly, ACR20 response rates after 24 weeks of LEF therapy were similar between patients switched from PLA to LEF without loading dose, and those who received a loading does of LEF (100 mg/day à 2 days) at randomization. Fewer adverse events were reported in patients switched to LEF without a loading dose. (J Rheumatol 2004;31:1521-31
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