562 research outputs found
Mass-Richness relations for X-ray and SZE-selected clusters at as seen by at 4.5m
We study the mass-richness relation of 116 spectroscopically-confirmed
massive clusters at by mining the archive. We
homogeneously measure the richness at 4.5m for our cluster sample within a
fixed aperture of radius and above a fixed brightness threshold,
making appropriate corrections for both background galaxies and foreground
stars. We have two subsamples, those which have a) literature X-ray
luminosities and b) literature Sunyaev-Zeldovich effect masses. For the X-ray
subsample we re-derive masses adopting the most recent calibrations. We then
calibrate an empirical mass-richness relation for the combined sample spanning
more than one decade in cluster mass and find the associated uncertainties in
mass at fixed richness to be dex. We study the dependance of the
scatter of this relation with galaxy concentration, defined as the ratio
between richness measured within an aperture radius of 1 and 2 arcminutes. We
find that at fixed aperture radius the scatter increases for clusters with
higher concentrations. We study the dependance of our richness estimates with
depth of the [4.5]m imaging data and find that reaching a depth of at
least [4.5]= 21 AB mag is sufficient to derive reasonable mass estimates. We
discuss the possible extension of our method to the mid-infrared all-sky
survey data, and the application of our results to the mission. This
technique makes richness-based cluster mass estimates available for large
samples of clusters at very low observational cost.Comment: Submitted to ApJ on Aug 31 2016, Revised version resubmitted on Apr
11th 201
Small-Scale structure in the Galactic ISM: Implications for Galaxy Cluster Studies
Observations of extragalactic objects need to be corrected for Galactic
absorption and this is often accomplished by using the measured 21 cm HI
column. However, within the beam of the radio telescope there are variations in
the HI column that can have important effects in interpreting absorption line
studies and X-ray spectra at the softest energies. We examine the HI and
DIRBE/IRAS data for lines of sight out of the Galaxy, which show evidence for
HI variations in of up to a factor of three in 1 degree fields. Column density
enhancements would preferentially absorb soft X-rays in spatially extended
objects and we find evidence for this effect in the ROSAT PSPC observations of
two bright clusters of galaxies, Abell 119 and Abell 2142.
For clusters of galaxies, the failure to include column density fluctuations
will lead to systematically incorrect fits to the X-ray data in the sense that
there will appear to be a very soft X-ray excess. This may be one cause of the
soft X-ray excess in clusters, since the magnitude of the effect is comparable
to the observed values.Comment: 16 pages, 9 figures, to appear in the Astrophysical Journal, vol. 597
(1 Nov 2003
The Quantity of Intracluster Light: Comparing Theoretical and Observational Measurement Techniques Using Simulated Clusters
Using a suite of N-body simulations of galaxy clusters specifically tailored
to study the intracluster light (ICL) component, we measure the quantity of ICL
using a number of different methods previously employed in the literature for
both observational and simulation data sets. By measuring the ICL of the
clusters using multiple techniques, we identify systematic differences in how
each detection method identifies the ICL. We find that techniques which define
the ICL solely based on the current position of the cluster luminosity, such as
a surface brightness or local density threshold, tend to find less ICL than
methods utilizing time or velocity information, including stellar particles'
density history or binding energy. The range of ICL fractions (the fraction of
the clusters' total luminosity found in the ICL component) we measure at z=0
across all our clusters using any definition span the range from 9-36%, and
even within a single cluster different methods can change the measured ICL
fraction by up to a factor of two. Separating the cluster's central galaxy from
the surrounding ICL component is a challenge for all ICL techniques, and
because the ICL is centrally concentrated within the cluster, the differences
in the measured ICL quantity between techniques are largely a consequence of
this central galaxy/ICL separation. We thoroughly explore the free parameters
involved with each measurement method, and find that adjusting these parameters
can change the measured ICL fraction by up to a factor of two. While for all
definitions the quantity of ICL tends to increase with time, the ICL fraction
does not grow at a uniform rate, nor even monotonically under some definitions.
Thus, the ICL can be used as a rough indicator of dynamical age, where more
dynamically advanced clusters will on average have higher ICL fractions.Comment: 18 pages, 11 figues. Accepted for publication in Ap
Role of DNA methylation in altered gene expression patterns in adult zebrafish (Danio rerio) exposed to 3, 3’, 4, 4’, 5-pentachlorobiphenyl (PCB 126)
© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Environmental Epigenetics 4 (2018): dvy005, doi:10.1093/eep/dvy005.There is growing evidence that environmental toxicants can affect various physiological processes by altering DNA methylation patterns. However, very little is known about the impact of toxicant-induced DNA methylation changes on gene expression patterns. The objective of this study was to determine the genome-wide changes in DNA methylation concomitant with altered gene expression patterns in response to 3, 3’, 4, 4’, 5-pentachlorobiphenyl (PCB126) exposure. We used PCB126 as a model environmental chemical because the mechanism of action is well-characterized, involving activation of aryl hydrocarbon receptor, a ligand-activated transcription factor. Adult zebrafish were exposed to 10 nM PCB126 for 24 h (water-borne exposure) and brain and liver tissues were sampled at 7 days post-exposure in order to capture both primary and secondary changes in DNA methylation and gene expression. We used enhanced Reduced Representation Bisulfite Sequencing and RNAseq to quantify DNA methylation and gene expression, respectively. Enhanced reduced representation bisulfite sequencing analysis revealed 573 and 481 differentially methylated regions in the liver and brain, respectively. Most of the differentially methylated regions are located more than 10 kilobases upstream of transcriptional start sites of the nearest neighboring genes. Gene Ontology analysis of these genes showed that they belong to diverse physiological pathways including development, metabolic processes and regeneration. RNAseq results revealed differential expression of genes related to xenobiotic metabolism, oxidative stress and energy metabolism in response to polychlorinated biphenyl exposure. There was very little correlation between differentially methylated regions and differentially expressed genes suggesting that the relationship between methylation and gene expression is dynamic and complex, involving multiple layers of regulation.This work was supported by the National Institute of Health Outstanding New Environmental Scientist Award to NA (NIH R01ES024915) and Woods Hole Center for Oceans and Human Health [National Institutes of Health (NIH) grant P01ES021923 and National Science Foundation Grant OCE-1314642 to M. Hahn, J. Stegeman, NA and SK]
Optical Colors of Intracluster Light in the Virgo Cluster Core
We continue our deep optical imaging survey of the Virgo cluster using the
CWRU Burrell Schmidt telescope by presenting B-band surface photometry of the
core of the Virgo cluster in order to study the cluster's intracluster light
(ICL). We find ICL features down to mu_b ~ 29 mag sq. arcsec, confirming the
results of Mihos et al. (2005), who saw a vast web of low-surface brightness
streams, arcs, plumes, and diffuse light in the Virgo cluster core using V-band
imaging. By combining these two data sets, we are able to measure the optical
colors of many of the cluster's low-surface brightness features. While much of
our imaging area is contaminated by galactic cirrus, the cluster core near the
cD galaxy, M87, is unobscured. We trace the color profile of M87 out to over
2000 arcsec, and find a blueing trend with radius, continuing out to the
largest radii. Moreover, we have measured the colors of several ICL features
which extend beyond M87's outermost reaches and find that they have similar
colors to the M87's halo itself, B-V ~ 0.8. The common colors of these features
suggests that the extended outer envelopes of cD galaxies, such as M87, may be
formed from similar streams, created by tidal interactions within the cluster,
that have since dissolved into a smooth background in the cluster potential.Comment: 14 pages. Published in ApJ, September 201
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Channel coincidence counter: version 1
A thermal neutron coincidence counter has been designed for the assay of fast critical assembly fuel drawers and plutonium-bearing fuel rods. The principal feature of the detector is a 7-cm by 7-cm by 97-cm detector channel, which provides a uniform neutron detection efficiency of 16% along the central 40 cm of the channel. The electronics system is identical to that used for the High-Level Neutron Coincidence Counter
Calibration and data quality of warm IRAC
We present an overview of the calibration and properties of data from the IRAC instrument aboard the Spitzer Space Telescope taken after the depletion of cryogen. The cryogen depleted on 15 May 2009, and shortly afterward a two-month- long calibration and characterization campaign was conducted. The array temperature and bias setpoints were revised on 19 September 2009 to take advantage of lower than expected power dissipation by the instrument and to improve sensitivity. The final operating temperature of the arrays is 28.7 K, the applied bias across each detector is 500 mV and the equilibrium temperature of the instrument chamber is 27.55 K. The final sensitivities are essentially the same as the cryogenic mission with the 3.6 ÎĽm array being slightly less sensitive (10%) and the 4.5 ÎĽm array within 5% of the cryogenic sensitivity. The current absolute photometric uncertainties are 4% at 3.6 and 4.5 ÎĽm, and better than milli-mag photometry is achievable for long-stare photometric observations. With continued analysis, we expect the absolute calibration to improve to the cryogenic value of 3%. Warm IRAC operations fully support all science that was conducted in the cryogenic mission and all currently planned warm science projects (including Exploration Science programs). We expect that IRAC will continue to make ground-breaking discoveries in star formation, the nature of the early universe, and in our understanding of the properties of exoplanets
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Expected precision of neutron multiplicity measurements of waste drums
DOE facilities are beginning to apply passive neutron multiplicity counting techniques to the assay of plutonium scrap and residues. There is also considerable interest in applying this new measurement technique to 208-liter waste drums. The additional information available from multiplicity counting could flag the presence of shielding materials or improve assay accuracy by correcting for matrix effects such as ({alpha},n) induced fission or detector efficiency variations. The potential for multiplicity analysis of waste drums, and the importance of better detector design, can be estimated by calculating the expected assay precision using a Figure of Merit code for assay variance. This paper reports results obtained as a function of waste drum content and detector characteristics. We find that multiplicity analysis of waste drums is feasible if a high-efficiency neutron counter is used. However, results are significantly poorer if the multiplicity analysis must be used to solve for detection efficiency
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