639 research outputs found
Properties of Faint Distant Galaxies as seen through Gravitational Telescopes
This paper reviews the most recent developments related to the use of lensing
clusters of galaxies as Gravitational Telescopes in deep Universe studies. We
summarize the state of the art and the most recent results aiming at studying
the physical properties of distant galaxies beyond the limits of conventional
spectroscopy. The application of photometric redshift techniques in the context
of gravitational lensing is emphasized for the study of both lensing structures
and the background population of lensed galaxies. A presently ongoing search
for the first building blocks of galaxies behind lensing clusters is presented
and discussed.Comment: Review lecture given at "Gravitational Lensing: a unique tool for
cosmology",Aussois, France, January 2003. To appear in ASP Conf. S., eds. D.
Valls-Gabaud & J.-P. Kneib, 26 pages, 8 figure
Microlensing of Broad Absorption Line Quasars: Polarization Variability
Roughly 10% of all quasars exhibit Broad Absorption Line (BAL) features which
appear to arise in material outflowing at high velocity from the active
galactic nucleus (AGN). The details of this outflow are, however, very poorly
constrained and the particular nature of the BAL material is essentially
unknown. Recently, new clues have become available through polarimetric studies
which have found that BAL troughs are more polarized than the quasar continuum
radiation. To explain these observations, models where the BAL material
outflows equatorially across the surface of the dusty torus have been
developed. In these models, however, several sources of the BAL polarization
are possible. Here, we demonstrate how polarimetric monitoring of
gravitationally lensed quasars, such as H 1413+117, during microlensing events
can not only distinguish between two currently popular models, but can also
provide further insight into the structure at the cores of BAL quasars.Comment: 17 pages, 3 figures, accepted to PAS
A Bayesian approach to strong lensing modelling of galaxy clusters
In this paper, we describe a procedure for modelling strong lensing galaxy
clusters with parametric methods, and to rank models quantitatively using the
Bayesian evidence. We use a publicly available Markov chain Monte-Carlo (MCMC)
sampler ('Bayesys'), allowing us to avoid local minima in the likelihood
functions. To illustrate the power of the MCMC technique, we simulate three
clusters of galaxies, each composed of a cluster-scale halo and a set of
perturbing galaxy-scale subhalos. We ray-trace three light beams through each
model to produce a catalogue of multiple images, and then use the MCMC sampler
to recover the model parameters in the three different lensing configurations.
We find that, for typical Hubble Space Telescope (HST)-quality imaging data,
the total mass in the Einstein radius is recovered with ~1-5% error according
to the considered lensing configuration. However, we find that the mass of the
galaxies is strongly degenerated with the cluster mass when no multiple images
appear in the cluster centre. The mass of the galaxies is generally recovered
with a 20% error, largely due to the poorly constrained cut-off radius.
Finally, we describe how to rank models quantitatively using the Bayesian
evidence. We confirm the ability of strong lensing to constrain the mass
profile in the central region of galaxy clusters in this way. Ultimately, such
a method applied to strong lensing clusters with a very large number of
multiple images may provide unique geometrical constraints on cosmology. The
implementation of the MCMC sampler used in this paper has been done within the
framework of the Lenstool software package, which is publicly available.Comment: Accepted to "Gravitational Lensing" Focus Issue of the New Journal of
Physics (invited), 35 pages, 11 figures at reduced resolutio
Detection of an Iron Emission Feature from the Lensed BAL QSO H1413+117 at z=2.56
We present the X-ray energy spectrum of the lensed BAL QSO H1413+117 (the
Cloverleaf) at z=2.56 observed with the Chandra X-ray observatory. We detected
293 photons in a 40 ks Advanced CCD Imaging Spectrometer (ACIS-S) observation.
The X-ray image consists of four lensed image components, thus the photons are
from the lensed QSO itself. The overall spectrum can be described with a
power-law function heavily absorbed by neutral matter at a redshift consistent
with the QSO redshift. This supports the idea that intrinsic absorption is
significant for BAL QSOs. The spectral fit significantly (99% confidence)
improves when we include an emission line. The centroid energy and intrinsic
width (Gaussian \sigma) of the line are 6.21 \pm 0.16 keV and 220
^{+270}_{-130} eV (90% errors), respectively, in the QSO rest frame, assuming
the absorbed power-law as the continuum. The equivalent width of the line in
the QSO rest frame is 960 ^{+1400}_{-480} eV. We suggest that the large
equivalent width, the centroid energy, and the line broadness can be explained
by iron K emission arising from X-ray reprocessing in the BAL flow, assuming it
has a conical thin-sheet structure.Comment: 3 figures, Accepted for publication in ApJ Letter
Determining the Cosmic Distance Scale from Interferometric Measurements of the Sunyaev-Zel'dovich Effect
We determine the distances to 18 galaxy clusters with redshifts ranging from
z~0.14 to z~0.78 from a maximum likelihood joint analysis of 30 GHz
interferometric Sunyaev-Zel'dovich effect (SZE) and X-ray observations. We
model the intracluster medium (ICM) using a spherical isothermal beta model. We
quantify the statistical and systematic uncertainties inherent to these direct
distance measurements, and we determine constraints on the Hubble parameter for
three different cosmologies. These distances imply a Hubble constant of 60 (+4,
-4) (+13, -18) km s-1 Mpc-1 for an Omega_M = 0.3, Omega_Lambda = 0.7 cosmology,
where the uncertainties correspond to statistical followed by systematic at 68%
confidence. With a sample of 18 clusters, systematic uncertainties clearly
dominate. The systematics are observationally approachable and will be
addressed in the coming years through the current generation of X-ray
satellites (Chandra & XMM-Newton) and radio observatories (OVRO, BIMA, & VLA).
Analysis of high redshift clusters detected in future SZE and X-ray surveys
will allow a determination of the geometry of the universe from SZE determined
distances.Comment: ApJ Submitted; 40 pages, 9 figures (fig 3 B&W for size constraint),
13 tables, uses emulateapj5 styl
Validation of the German Revised Addenbrooke's Cognitive Examination for Detecting Mild Cognitive Impairment, Mild Dementia in Alzheimer's Disease and Frontotemporal Lobar Degeneration
Background/Aims: The diagnostic accuracy of the German version of the revised Addenbrooke's Cognitive Examination (ACE-R) in identifying mild cognitive impairment (MCI), mild dementia in Alzheimer's disease (AD) and mild dementia in frontotemporal lobar degeneration (FTLD) in comparison with the conventional Mini Mental State Examination (MMSE) was assessed. Methods: The study encompasses 76 cognitively healthy elderly individuals, 75 patients with MCI, 56 with AD and 22 with FTLD. ACE-R and MMSE were validated against an expert diagnosis based on a comprehensive diagnostic procedure. Statistical analysis was performed using the receiver operating characteristic method and regression analyses. Results: The optimal cut-off score for the ACE-R for detecting MCI, AD, and FTLD was 86/87, 82/83 and 83/84, respectively. ACE-R was superior to MMSE only in the detection of patients with FTLD {[}area under the curve (AUC): 0.97 vs. 0.92], whilst the accuracy of the two instruments did not differ in identifying MCI and AD. The ratio of the scores of the memory ACE-R subtest to verbal fluency subtest contributed significantly to the discrimination between AD and FTLD (optimal cut-off score: 2.30/2.31, AUC: 0.77), whereas the MMSE and ACE-R total scores did not. Conclusion: The German ACE-R is superior to the most commonly employed MMSE in detecting mild dementia in FTLD and in the differential diagnosis between AD and FTLD. Thus it might serve as a valuable instrument as part of a comprehensive diagnostic workup in specialist centres/clinics contributing to the diagnosis and differential diagnosis of the cause of dementia. Copyright (C) 2010 S. Karger AG, Base
A Multiwavelength Analysis of the Strong Lensing Cluster RCS 022434-0002.5 at z=0.778
We present the results of two (101 ks total) Chandra observations of the
z=0.778 optically selected lensing cluster RCS022434-0002.5, along with weak
lensing and dynamical analyses of this object. An X-ray spectrum extracted
within R(2500) (362 h(70)^(-1) kpc) results in an integrated cluster
temperature of 5.1 (+0.9,-0.5) keV. The surface brightness profile of
RCS022434-0002.5 indicates the presence of a slight excess of emission in the
core. A hardness ratio image of this object reveals that this central emission
is primarily produced by soft X-rays. Further investigation yields a cluster
cooling time of 3.3 times 10^9 years, which is less than half of the age of the
universe at this redshift given the current LCDM cosmology. A weak lensing
analysis is performed using HST images, and our weak lensing mass estimate is
found to be in good agreement with the X-ray determined mass of the cluster.
Spectroscopic analysis reveals that RCS022434-0002.5 has a velocity dispersion
of 900 +/- 180 km/s, consistent with its X-ray temperature. The core gas mass
fraction of RCS022434-0002.5 is, however, found to be three times lower than
expected universal values. The radial distribution of X-ray point sources
within R(200) of this cluster peaks at ~0.7 R(200), possibly indicating that
the cluster potential is influencing AGN activity at that radius. Correlations
between X-ray and radio (VLA) point source positions are also examined.Comment: 32 pages, 9 figures. Accepted for publication in The Astrophysical
Journa
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