3,531 research outputs found
Measurement of the Mass Profile of Abell 1689
In this letter we present calibrated mass and light profiles of the rich
cluster of galaxies Abell 1689 out to 1 Mpc from the center. The high
surface density of faint blue galaxies at high redshift, selected by their low
surface brightness, are unique tools for mapping the projected mass
distribution of foreground mass concentrations. The systematic gravitational
lens distortions of of these background galaxies in 15\arcmin\ fields
reveal detailed mass profiles for intervening clusters of galaxies, and are a
direct measure of the growth of mass inhomogeneity. The mass is measured
directly, avoiding uncertainties encountered in velocity or X-ray derived mass
estimates.
Mass in the rich cluster Abell 1689 follows smoothed light, outside 100
h kpc, with a rest-frame V band mass-to-light ratio of
. Near the cluster center, mass appears to be more
smoothly distributed than light. Out to a radius of 1 Mpc the total
mass follows a steeper than isothermal profile. Comparing with preliminary high
resolution N-body clustering simulations for various cosmogonies on these
scales, these data are incompatible with hot dark matter, a poor fit to most
mixed dark matter models, and favor open or cold dark matter.
Substructure is seen in both the mass and the light, but detailed
correspondence is erased on scales less than 100 kpc.Comment: 13 pages, uuencoded, compressed postscript file, 2 figures included
additional 1Mbyte figure available on request. Only change is that in
original errorbars on Fig. 5 were a factor of 2 too big
Discovery of a Galaxy Cluster via Weak Lensing
We report the discovery of a cluster of galaxies via its weak gravitational
lensing effect on background galaxies, the first spectroscopically confirmed
cluster to be discovered through its gravitational effects rather than by its
electromagnetic radiation. This fundamentally different selection mechanism
promises to yield mass-selected, rather than baryon or photon-selected, samples
of these important cosmological probes. We have confirmed this cluster with
spectroscopic redshifts of fifteen members at z=0.276, with a velocity
dispersion of 615 km/s. We use the tangential shear as a function of source
photometric redshift to estimate the lens redshift independently and find z_l =
0.30 +- 0.08. The good agreement with the spectroscopy indicates that the
redshift evolution of the mass function may be measurable from the imaging data
alone in shear-selected surveys.Comment: revised version with minor changes, to appear in ApJ
Wide-field weak lensing by RXJ1347-1145
We present an analysis of weak lensing observations for RXJ1347-1145 over a
43' X 43' field taken in B and R filters on the Blanco 4m telescope at CTIO.
RXJ1347-1145 is a massive cluster at redshift z=0.45. Using a population of
galaxies with 20<R<26, we detect a weak lensing signal at the p<0.0005 level,
finding best-fit parameters of \sigma_v=1400^{+130}_{-140} km s^{-1} for a
singular isothermal sphere model and r_{200} = 3.5^{+0.8}_{-0.2} Mpc with c =
15^{+64}_{-10} for a NFW model in an \Omega_m = 0.3, \Omega_\Lambda = 0.7
cosmology. In addition, a mass to light ratio M/L_R =90 \pm 20 M_\odot /
L_{R\odot} was determined. These values are consistent with the previous weak
lensing study of RXJ1347--1145 by Fischer and Tyson, 1997, giving strong
evidence that systemic bias was not introduced by the relatively small field of
view in that study. Our best-fit parameter values are also consistent with
recent X-ray studies by Allen et al, 2002 and Ettori et al, 2001, but are not
consistent with recent optical velocity dispersion measurements by Cohen and
Kneib, 2002.Comment: accepted to ApJ, tentative publication 10 May 2005, v624
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The Rapid Determination of Chemical Oxygen Demand in Waste Waters and Effluents using Flow Injection Analysis
Measuring Baryon Acoustic Oscillations with Millions of Supernovae
Since type Ia Supernovae (SNe) explode in galaxies, they can, in principle,
be used as the same tracer of the large-scale structure as their hosts to
measure baryon acoustic oscillations (BAOs). To realize this, one must obtain a
dense integrated sampling of SNe over a large fraction of the sky, which may
only be achievable photometrically with future projects such as the Large
Synoptic Survey Telescope. The advantage of SN BAOs is that SNe have more
uniform luminosities and more accurate photometric redshifts than galaxies, but
the disadvantage is that they are transitory and hard to obtain in large number
at high redshift. We find that a half-sky photometric SN survey to redshift z =
0.8 is able to measure the baryon signature in the SN spatial power spectrum.
Although dark energy constraints from SN BAOs are weak, they can significantly
improve the results from SN luminosity distances of the same data, and the
combination of the two is no longer sensitive to cosmic microwave background
priors.Comment: 4 pages, 3 figures, ApJL accepte
A Bayesian Approach to the Detection Problem in Gravitational Wave Astronomy
The analysis of data from gravitational wave detectors can be divided into
three phases: search, characterization, and evaluation. The evaluation of the
detection - determining whether a candidate event is astrophysical in origin or
some artifact created by instrument noise - is a crucial step in the analysis.
The on-going analyses of data from ground based detectors employ a frequentist
approach to the detection problem. A detection statistic is chosen, for which
background levels and detection efficiencies are estimated from Monte Carlo
studies. This approach frames the detection problem in terms of an infinite
collection of trials, with the actual measurement corresponding to some
realization of this hypothetical set. Here we explore an alternative, Bayesian
approach to the detection problem, that considers prior information and the
actual data in hand. Our particular focus is on the computational techniques
used to implement the Bayesian analysis. We find that the Parallel Tempered
Markov Chain Monte Carlo (PTMCMC) algorithm is able to address all three phases
of the anaylsis in a coherent framework. The signals are found by locating the
posterior modes, the model parameters are characterized by mapping out the
joint posterior distribution, and finally, the model evidence is computed by
thermodynamic integration. As a demonstration, we consider the detection
problem of selecting between models describing the data as instrument noise, or
instrument noise plus the signal from a single compact galactic binary. The
evidence ratios, or Bayes factors, computed by the PTMCMC algorithm are found
to be in close agreement with those computed using a Reversible Jump Markov
Chain Monte Carlo algorithm.Comment: 19 pages, 12 figures, revised to address referee's comment
Design and operation of an autosampler controlled flow-injection preconcentration system for lead determination by flame atomic absorption spectrometry
Flow-injection manifolds are described which allow the preconcentration
of lead for flame atomic absorption determinations, using
columns contained within the sample loop of an injection valve. An
interface was designed which allowed the valves and pump in the
system to be controlled by an autosampler which enabled precise
timing of preconcentration and elution steps. The effects of sample
flow rate, buffer pH and buffer type for preconcentration and
eluent concentration and flow rate were investigated in order to
obtain optimum performance of the system. A 50-times improvement
in detection limits over conventional sample introduction was
obtained for a sample volume of approximately 12 ml, preconcentrated for
150 s. The injection of eluent, as opposed to the use of a
continuously flowing eluent stream, enabled this reagent to be
conserved
The results of deep CCD field surveys: Very low mass halo population stars as dark matter
Halo and disk M dwarfs differ significantly in metallicity. Multi‐color deep CCD surveys are uniquely capable of detecting these separate populations of stars with differing metallicity and therefore colors. Analyzing very deep three‐band CCD images covering 192 arcmin2 at high galactic latitude we find no evidence for a population of extreme low mass M subdwarfs sufficient to account for the halo dark matter. These observations covering a volume of 2×105 pc3 are consistent with extrapolations of a halo luminosity function determined using low metallicity stars in the solar neighborhood. © 1995 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87546/2/91_1.pd
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