2,754 research outputs found
Near-IR imaging of moderate redshift galaxy clusters
We have obtained near-IR imaging of 3 moderate-z clusters on the 1.3 m at KPNO with SQIID, a new camera offering wide-field (5.5 arcmin) simultaneous JHK band imaging. Our photometry on a sample of approximately 100 likely member galaxies in one of the clusters, Abell 370 at z = 0.37, shows that we can obtain magnitudes good to 20 percent down to K = 18, considerably below the estimated K* = 16.5 at this redshift. These data indicate that there are no systematic problems in obtaining photometry at faint levels with SQIID. With the development of larger arrays, the field is open to progress. The resulting J, H, and K data for three clusters are combined with previously obtained multiband optical photometry. We present an investigation of the spectral properties and evolution of the dominant cold stellar populations by comparing optical-to-IR colors and color-magnitude diagrams to predictions from population synthesis models and galaxy spectral evolution codes
Desynchronization of pathological low-frequency brain activity by the hypnotic drug zolpidem.
Reports of the beneficial effects of the hypnotic imidazopyridine, zolpidem, described in persistent vegetative state^1, 2^ have been replicated recently in brain-injured and cognitively impaired patients^3-7^. Previous single photon emission computed tomography (SPECT) studies have suggested that sub-sedative doses of zolpidem increased regional cerebral perfusion in affected areas^5, 8^, implying enhanced neuronal metabolic activity; which has led to speculation that zolpidem 'reawakens' functionally dormant cortex. However, a neuronal mechanism by which this hypnotic drug affords benefits to brain injured patients has yet to be demonstrated. Here, we report the action of sub-sedative doses of zolpidem on neuronal network oscillatory activity in human brain, measured using pharmaco-magnetoencephalography (pharmaco-MEG). Study participant JP suffered a stroke in 1996, causing major damage to the left hemisphere that impaired aspects of both motor and cognitive function. Pharmaco-MEG analyses revealed robust and persistent pathological theta (4-10Hz) and beta (15-30Hz) oscillations within the lesion penumbra and surrounding cortex. Administration of zolpidem (5mg) reduced the power of pathological theta and beta oscillations in all regions of the lesioned hemisphere. This desynchronizing effect correlated well with zolpidem uptake (occurring approximately 40 minutes after acute administration) and was coincident with marked improvements in cognitive and motor function. Control experiments revealed no effect of placebo, while a structurally unrelated hypnotic, zopiclone, administered at a comparable dose (3.5mg) elicited widespread increases in cortical oscillatory power in the beta (15-30Hz) band without functional improvement. These results suggest that in JP, specific motor and cognitive impairments are related to increased low-frequency oscillatory neuronal network activity. Zolpidem is unique amongst hypnotic drugs in its ability to desynchronize such pathological low-frequency activity, thereby restoring cognitive function
Age-specific incidence of A/H1N1 2009 influenza infection in England from sequential antibody prevalence data using likelihood-based estimation.
Estimating the age-specific incidence of an emerging pathogen is essential for understanding its severity and transmission dynamics. This paper describes a statistical method that uses likelihoods to estimate incidence from sequential serological data. The method requires information on seroconversion intervals and allows integration of information on the temporal distribution of cases from clinical surveillance. Among a family of candidate incidences, a likelihood function is derived by reconstructing the change in seroprevalence from seroconversion following infection and comparing it with the observed sequence of positivity among the samples. This method is applied to derive the cumulative and weekly incidence of A/H1N1 pandemic influenza in England during the second wave using sera taken between September 2009 and February 2010 in four age groups (1-4, 5-14, 15-24, 25-44 years). The highest cumulative incidence was in 5-14 year olds (59%, 95% credible interval (CI): 52%, 68%) followed by 1-4 year olds (49%, 95% CI: 38%, 61%), rates 20 and 40 times higher respectively than estimated from clinical surveillance. The method provides a more accurate and continuous measure of incidence than achieved by comparing prevalence in samples grouped by time period
Monte Carlo Comparisons to a Cryogenic Dark Matter Search Detector with low Transition-Edge-Sensor Transition Temperature
We present results on phonon quasidiffusion and Transition Edge Sensor (TES)
studies in a large, 3 inch diameter, 1 inch thick [100] high purity germanium
crystal, cooled to 50 mK in the vacuum of a dilution refrigerator, and exposed
with 59.5 keV gamma-rays from an Am-241 calibration source. We compare
calibration data with results from a Monte Carlo which includes phonon
quasidiffusion and the generation of phonons created by charge carriers as they
are drifted across the detector by ionization readout channels. The phonon
energy is then parsed into TES based phonon readout channels and input into a
TES simulator
Problems with Using Evolutionary Theory in Philosophy
Does science move toward truths? Are present scientific theories (approximately) true? Should we invoke truths to explain the success of science? Do our cognitive faculties track truths? Some philosophers say yes, while others say no, to these questions. Interestingly, both groups use the same scientific theory, viz., evolutionary theory, to defend their positions. I argue that it begs the question for the former group to do so because their positive answers imply that evolutionary theory is warranted, whereas it is self-defeating for the latter group to do so because their negative answers imply that evolutionary theory is unwarranted
The Fundamental Plane at z=1.27: First Calibration of the Mass Scale of Red Galaxies at Redshifts z>1
We present results on the Fundamental Plane (FP) of early-type galaxies in
the cluster RDCS J0848+4453 at z=1.27. Internal velocity dispersions of three
K-selected early-type galaxies are determined from deep Keck spectra.
Structural parameters are determined from HST NICMOS images. The galaxies show
substantial offsets from the FP of the nearby Coma cluster, as expected from
passive evolution of their stellar populations. The offsets from the FP can be
expressed as offsets in M/L ratio. The M/L ratios of the two most massive
galaxies are consistent with an extrapolation of results obtained at
z=0.02-0.83. The evolution of early-type galaxies with masses >10^11 M_sun is
well described by ln M/L(B) = (-1.06 +- 0.09) z, corresponding to passive
evolution of -1.50 +- 0.13 mag at z=1.3. Ignoring selection effects, the best
fitting stellar formation redshift is z*=2.6, corresponding to a luminosity
weighted age at the epoch of observation of ~2 Gyr. The M/L ratios of these two
galaxies are also in excellent agreement with predictions from models that
include progenitor bias. The third galaxy is a factor ~10 less massive than the
other two, shows strong Balmer absorption lines in its spectrum, and is offset
from the Coma Fundamental Plane by 2.9 mag in rest-frame B. Despite their large
range in M/L ratios, all three galaxies fall in the ``Extremely Red Object''
(ERO) class with I-H>3 and R-K>5, and our results show that it is hazardous to
use simple models for converting luminosity to mass for these objects.
Measurements of M/L ratios at high redshift can be considered first steps to
empirically disentangle luminosity and mass evolution at the high mass end of
the galaxy population, lifting an important degeneracy in the interpretation of
evolution of the luminosity function. [SHORTENED]Comment: Accepted for publication in the Astrophysical Journa
Scaling Relations and Overabundance of Massive Clusters at z>~1 from Weak-Lensing Studies with HST
We present weak gravitational lensing analysis of 22 high-redshift (z >~1)
clusters based on Hubble Space Telescope images. Most clusters in our sample
provide significant lensing signals and are well detected in their
reconstructed two-dimensional mass maps. Combining the current results and our
previous weak-lensing studies of five other high-z clusters, we compare
gravitational lensing masses of these clusters with other observables. We
revisit the question whether the presence of the most massive clusters in our
sample is in tension with the current LambdaCDM structure formation paradigm.
We find that the lensing masses are tightly correlated with the gas
temperatures and establish, for the first time, the lensing mass-temperature
relation at z >~ 1. For the power law slope of the M-TX relation (M propto
T^{\alpha}), we obtain \alpha=1.54 +/- 0.23. This is consistent with the
theoretical self-similar prediction \alpha=3/2 and with the results previously
reported in the literature for much lower redshift samples. However, our
normalization is lower than the previous results by 20-30%, indicating that the
normalization in the M-TX relation might evolve. After correcting for Eddington
bias and updating the discovery area with a more conservative choice, we find
that the existence of the most massive clusters in our sample still provides a
tension with the current Lambda CDM model. The combined probability of finding
the four most massive clusters in this sample after marginalization over
current cosmological parameters is less than 1%.Comment: ApJ in press. See http://www.supernova.lbl.gov for additional
information pertaining to the HST Cluster SN Surve
The WIRCAM Deep Infrared Cluster Survey I: Groups and Clusters at z > 1.1
We use CFHTLS deep optical data, WIRCam Deep Survey (WIRDS) NIR data and XMM
data to identify z>1.1 clusters in the CFHTLS D1 and D4 fields. Counterparts to
such clusters can not be identified without deep NIR data and as such the total
of =1deg2 of J , H & Ks band imaging provided by WIRDS is an indispensable tool
in such work. Using public XMM X-ray data, we identify extended X-ray sources
in the two fields. The resulting catalogue of extended X-ray sources was
analyzed for optical/NIR counterparts, using a red-sequence algorithm.
Redshifts of candidate groups and clusters were estimated using the median
photometric redshifts of detected counterparts and where available
spectroscopic data. Additionally, we surveyed X-ray point sources for potential
group systems at the limit of our detection range in the X-ray data. A
catalogue of z > 1.1 cluster candidates in the two fields has been compiled and
cluster masses, radii and temperatures have been estimated using the scaling
relations. The catalogue consists of 15 z > 1.1 candidates. Three of the
detections are previously published extended X-ray sources. Of note is JKSC 041
for which we identify possible structures at z = 0.8, z = 0.96, z = 1.13 and z
= 1.49. We also make an independent detection of the massive cluster, XMMXCS
J2215.9-1738. We use the z > 1.1 catalogue to compare the cluster number counts
in these fields with models based on WMAP 7-year cosmology and find that the
models slightly over-predict the observations, whilst at z>1.5 we do not detect
any clusters. We note that cluster number counts at z > 1.1 are highly
sensitive to the cosmological model, however a significant reduction in present
statistical (due to available survey area) and systematic (due to cluster
scaling relations) uncertainties is required in order to confidently constrain
cosmological parameters using cluster number counts at high redshift.Comment: 22 pages, 22 figures, Accepted 4 August 201
Constructing a WISE High Resolution Galaxy Atlas
After eight months of continuous observations, the Wide-field Infrared Survey
Explorer (WISE) mapped the entire sky at 3.4 {\mu}m, 4.6 {\mu}m, 12 {\mu}m and
22 {\mu}m. We have begun a dedicated WISE High Resolution Galaxy Atlas (WHRGA)
project to fully characterize large, nearby galaxies and produce a legacy image
atlas and source catalogue. Here we summarize the deconvolution technique used
to significantly improve the spatial resolution of WISE imaging, specifically
designed to study the internal anatomy of nearby galaxies. As a case study, we
present results for the galaxy NGC 1566, comparing the WISE super-resolution
image processing to that of Spitzer, GALEX and ground-based imaging. The is the
first paper in a two part series; results for a much larger sample of nearby
galaxies is presented in the second paper.Comment: Published in the AJ (2012, AJ, 144, 68
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