382 research outputs found
New Modeling of the Lensing Galaxy and Cluster of Q0957+561: Implications for the Global Value of the Hubble Constant
The gravitational lens 0957+561 is modeled utilizing recent observations of
the galaxy and the cluster as well as previous VLBI radio data which have been
re-analyzed recently. The galaxy is modeled by a power-law elliptical mass
density with a small core while the cluster is modeled by a non-singular
power-law sphere as indicated by recent observations. Using all of the current
available data, the best-fit model has a reduced chi-squared of approximately 6
where the chi-squared value is dominated by a small portion of the
observational constraints used; this value of the reduced chi-squared is
similar to that of the recent FGSE best-fit model by Barkana et al. However,
the derived value of the Hubble constant is significantly different from the
value derived from the FGSE model. We find that the value of the Hubble
constant is given by H_0 = 69 +18/-12 (1-K) and 74 +18/-17 (1-K) km/s/Mpc with
and without a constraint on the cluster's mass, respectively, where K is the
convergence of the cluster at the position of the galaxy and the range for each
value is defined by Delta chi-squared = reduced chi-squared. Presently, the
best achievable fit for this system is not as good as for PG 1115+080, which
also has recently been used to constrain the Hubble constant, and the
degeneracy is large. Possibilities for improving the fit and reducing the
degeneracy are discussed.Comment: 22 pages in aaspp style including 6 tables and 5 figures, ApJ in
press (Nov. 1st issue
CFHT AO Imaging of the CLASS Gravitational Lens System B1359+154
We present adaptive optics imaging of the CLASS gravitational lens system
B1359+154 obtained with the Canada-France-Hawaii Telescope (CFHT) in the
infrared K band. The observations show at least three brightness peaks within
the ring of lensed images, which we identify as emission from multiple lensing
galaxies. The results confirm the suspected compound nature of the lens, as
deduced from preliminary mass modeling. The detection of several additional
nearby galaxies suggests that B1359+154 is lensed by the compact core of a
small galaxy group. We attempted to produce an updated lens model based on the
CFHT observations and new 5-GHz radio data obtained with the MERLIN array, but
there are too few constraints to construct a realistic model at this time. The
uncertainties inherent with modeling compound lenses make B1359+154 a
challenging target for Hubble constant determination through the measurement of
differential time delays. However, time delays will offer additional
constraints to help pin down the mass model. This lens system therefore
presents a unique opportunity to directly measure the mass distribution of a
galaxy group at intermediate redshift.Comment: 12 pages including 3 figures; ApJL accepte
Smoothing Algorithms and High-order Singularities in Gravitational Lensing
We propose a new smoothing method for obtaining surface densities from
discrete particle positions from numerical simulations. This is an essential
step for many applications in gravitational lensing. This method is based on
the ``scatter'' interpretation of the discrete density field in the Smoothed
Particle Hydrodynamics. We use Monte Carlo simulations of uniform density
fields and one isothermal ellipsoid to empirically derive the noise properties,
and best smoothing parameters (such as the number of nearest neighbors used). A
cluster from high-resolution simulations is then used to assess the reality of
high-order singularities such as swallowtails and butterflies in caustics,
which are important for the interpretation of substructures in gravitational
lenses. We also compare our method with the Delaunay tesselation field
estimator using the galaxy studied by Bradac et al. (2004), and find good
agreements. We show that higher order singularities are not only connected with
bound subhaloes but also with the satellite streams. However, the presence of
high-order singularities are sensitive to not only the fluctuation amplitude of
the surface density, but also the detailed form of the underlying smooth
lensing potential (such as ellipticity and external shear).Comment: ApJ, Accepted,(Released November 1st). The high resolution figures
are availabel at http://202.127.29.4/mppg/english/data
Exploratory Study of the X-Ray Properties of Quasars With Intrinsic Narrow Absorption Lines
We have used archival Chandra and XMM-Newton observations of quasars hosting
intrinsic narrow UV absorption lines (intrinsic NALs) to carry out an
exploratory survey of their X-ray properties. Our sample consists of three
intrinsic-NAL quasars and one "mini-BAL" quasar, plus four quasars without
intrinsic absorption lines for comparison. These were drawn in a systematic
manner from an optical/UV-selected sample. The X-ray properties of
intrinsic-NAL quasars are indistinguishable from those of "normal" quasars. We
do not find any excess absorption in quasars with intrinsic NALs, with upper
limits of a few times 10^22 cm^-2. We compare the X-ray and UV properties of
our sample quasars by plotting the equivalent width and blueshift velocity of
the intrinsic NALs and the X-ray spectral index against the "optical-to-X-ray"
slope, alpha-ox. When BAL quasars and other AGNs with intrinsic NALs are
included, the plots suggest that intrinsic-NAL quasars form an extension of the
BAL sequences and tend to bridge the gap between BAL and "normal" quasars.
Observations of larger samples of intrinsic-NAL quasars are needed to verify
these conclusions. We also test two competing scenarios for the location of the
NAL gas in an accretion-disk wind. Our results strongly support a location of
the NAL gas at high latitudes above the disk, closer to the disk axis than the
dense BAL wind. We detect excess X-ray absorption only in Q0014+8118, which
does not host intrinsic NALs. The absorbing medium very likely corresponds to
an intervening system at z=1.1, which also produces strong absorption lines in
the rest-frame UV spectrum of this quasar. In the appendix we discuss the
connection between UV and X-ray attenuation and its effect on alpha-ox.Comment: Accepted by the Astrophysical Journa
CX3CR1 Polymorphisms are associated with atopy but not asthma in German children
Chemokines and their receptors are involved in many aspects of immunity. Chemokine CX3CL1, acting via its receptor CX3CR1, regulates monocyte migration and macrophage differentiation as well as T cell-dependent inflammation. Two common, nonsynonymous polymorphisms in CX3CR1 have previously been shown to alter the function of the CX3CL1/CX3CR1 pathway and were suggested to modify the risk for asthma. Using matrix-assisted laser desorption/ionization time-of-flight technology, we genotyped polymorphisms Val249Ile and Thr280Met in a cross-sectional population of German children from Munich (n = 1,159) and Dresden ( n = 1,940). For 249Ile an odds ratio of 0.77 (95% confidence interval 0.63-0.96; p = 0.017) and for 280Met an odds ratio of 0.71 ( 95% confidence interval 0.56-0.89; p = 0.004) were found with atopy in Dresden but not in Munich. Neither polymorphism was associated with asthma. Thus, amino acid changes in CX3CR1 may influence the development of atopy but not asthma in German children. Potentially, other factors such as environmental effects may modify the role of CX3CR1 polymorphisms. Copyright (c) 2007 S. Karger AG, Basel
Testing a new analytic model for gravitational lensing probabilities
We study gravitational lensing with a multiple lens plane approach, proposing
a simple analytical model for the probability distribution function (PDF) of
the dark matter convergence, kappa, for the different lens planes in a given
cosmology as a function of redshift and smoothing angle, theta. The model is
fixed solely by the variance of kappa, which in turn is fixed by the amplitude
of the power spectrum, sigma_8. We test the PDF against a high resolution
Tree-Particle-Mesh simulation and find that it is far superior to the Gaussian
or the lognormal, especially for small values of theta << 1 arcmin and at large
values of kappa relevant to strong lensing. With this model, we predict the
probabilities of strong lensing by a single plane or by multiple planes. We
find that for theta ~ 10 arcsec, a single plane accounts for almost all (~ 98%)
of the strong lensing cases for source redshift unity. However, for a more
typical source redshift of 4, about 12% of the strong lensing cases will result
from the contribution of a secondary clump of matter along the line of sight,
introducing a systematic error in the determination of the surface density of
clusters, typically overestimating it by about 2-5%. We also find that matter
inhomogenieties introduce a dispersion in the value of the angular diameter
distance about its cosmological mean. The probable error relative to the mean
increases with redshift to a value of about 8% for z ~ 6 and theta ~ 10 arcsec.Comment: Accepted for publication in ApJ, 13 pages, 12 figures, revised
version, references added, section 6 expande
Corporate Governance, Opaque Bank Activities, and Risk/Return Efficiency: Pre- and Post-Crisis Evidence from Turkey
Does better corporate governance unambiguously improve the risk/return efficiency of banks? Or does either a re-orientation of banks' revenue mix towards more opaque products, an economic downturn, or tighter supervision create off-setting or reinforcing effects? The authors relate bank efficiency to shortfalls from a stochastic risk/return frontier. They analyze how internal governance mechanisms (CEO duality, board experience, political connections, and education profile) and external governance mechanisms (discipline exerted by shareholders, depositors, or skilled employees) determine efficiency in a sample of Turkish banks. The 2000 financial crisis was a wakeup call for bank efficiency and corporate governance. As a result, better corporate governance mechanisms have been able to improve risk/return efficiency when the economic, regulatory, and supervisory environments are more stable and bank products are more complex.corporate governance;bank risk;noninterest income;crisis;frontier
Gravitational Waveguides in Cosmology
We discuss the possibility that, besides the usual gravitational lensing,
there may exist a sort of gravitational waveguiding in cosmology which could
explain some anomalous phenomena which cannot be understood by the current
gravitational lensing models as the existence of "brothers" objects having
different brilliancy but similar spectra and redshifts posed on the sky with
large angular distance. Furthermore, such a phenomena could explain the huge
luminosities coming from quasars using the cosmological structures as
selfoc-type or planar waveguide. We describe the gravitational waveguide theory
and then we discuss possible realizations in cosmology.Comment: 14 pages, latex, submitted to Int. Jou. Mod. Phys.
CLASS B1152+199 and B1359+154: Two New Gravitational Lens Systems Discovered in the Cosmic Lens All-Sky Survey
The third phase of the Cosmic Lens All-Sky Survey (CLASS) has recently been
completed, bringing the total number of sources imaged to over 15000 in the
CLASS and JVAS combined survey. In the VLA observations carried out in March
and April of 1998, two new candidate lensed systems were discovered: CLASS
B1152+199 and B1359+154. B1152+199 is a 1.6 arcsecond double, with a background
quasar at z=1.019 lensed by a foreground galaxy at z=0.439. The relatively flat
radio spectra of the lensed images, combined with a previous ROSAT detection of
the source, make B1152+199 a strong candidate for time delay studies at both
radio and X-ray wavelengths. B1359+154 is a quadruply lensed quasar at z=3.235,
with a maximum image separation of 1.7 arcseconds. As yet, the redshift of the
lensing object in this system is undetermined. The steep spectral index of the
source suggests that B1359+154 will not exhibit strong variability, and is
therefore unlikely to be useful for determining the Hubble constant from
measured time delays.Comment: accepted for publication in The Astronomical Journa
Transport and build-up of tropospheric trace gases during the MINOS campaign: comparision of GOME, in situ aircraft measurements and MATCH-MPIC-data
The MINOS (Mediterranean INtensive Oxidant Study) campaign was an international, multi-platform field campaign to measure long-range transport of air-pollution and aerosols from South East Asia and Europe towards the Mediterranean basin during August 2001. High pollution events were observed during this campaign. For the Mediterranean region enhanced tropospheric nitrogen dioxide (NO<sub>2</sub>) and formaldehyde (HCHO), which are precursors of tropospheric ozone (O<sub>3</sub>), were detected by the satellite based GOME (Global Ozone Monitoring Experiment) instrument and compared with airborne in situ measurements as well as with the output from the global 3D photochemistry-transport model MATCH-MPIC (Model of Atmospheric Transport and CHemistry - Max Planck Institute for Chemistry). The increase of pollution in that region leads to severe air quality degradation with regional and global implications
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