50,605 research outputs found
Wide field weak lensing observations of A1835 and A2204
We present mass reconstructions from weak lensing for the galaxy clusters
A1835 and A2204 over 34'x34' fields using data from the ESO/MPG Wide Field
Imager. Using a background galaxy population of 22<R<25.5 we detect the
gravitational shear of A1835 at 8.8 sigma significance, and obtain best-fit
mass profiles of sigma_v=1233^{+66}_{-70} km/s for a singular isothermal sphere
model and r_{200}=1550 h^{-1} kpc, c=2.96 for a `universal' CDM profile. Using
a color-selected background galaxy population of 22<R<25.8 we detect the
gravitational shear of A2204 at 7.2 sigma significance, and obtain best-fit
mass profiles of sigma_v=1035^{+65}_{-71} km/s for a SIS model and r_{200}=1310
h^{-1} km/s, c=6.3 for a `universal' CDM profile. The gravitational shear at
distances greater than 10' is significantly detected for both clusters. The
best fit weak lensing cluster masses agree well with both X-ray and dynamical
mass measurements, although the central concentration of A1835 is much lower in
the weak lensing mass profile than that measured by recent Chandra results. We
suggest that this lower concentration is most likely a combination of
contamination of the 'background' galaxy population with cluster dwarf galaxies
and the effect of a prolate or tri-axial cluster core with the major axis lying
near the plane of the sky. We also detect a number of additional structures at
moderate significance, some of which appear to be sub-haloes associated with
the clusters.Comment: accepted to A&A, 14 pages, 13 figures, version with higher quality
images can be found at http://www.uni-bonn.de/~clow
Constrained probability distributions of correlation functions
Context: Two-point correlation functions are used throughout cosmology as a
measure for the statistics of random fields. When used in Bayesian parameter
estimation, their likelihood function is usually replaced by a Gaussian
approximation. However, this has been shown to be insufficient.
Aims: For the case of Gaussian random fields, we search for an exact
probability distribution of correlation functions, which could improve the
accuracy of future data analyses.
Methods: We use a fully analytic approach, first expanding the random field
in its Fourier modes, and then calculating the characteristic function.
Finally, we derive the probability distribution function using integration by
residues. We use a numerical implementation of the full analytic formula to
discuss the behaviour of this function.
Results: We derive the univariate and bivariate probability distribution
function of the correlation functions of a Gaussian random field, and outline
how higher joint distributions could be calculated. We give the results in the
form of mode expansions, but in one special case we also find a closed-form
expression. We calculate the moments of the distribution and, in the univariate
case, we discuss the Edgeworth expansion approximation. We also comment on the
difficulties in a fast and exact numerical implementation of our results, and
on possible future applications.Comment: 13 pages, 5 figures, updated to match version published in A&A
(slightly expanded Sects. 5.3 and 6
Generalized Robba rings
We prove that any projective coadmissible module over the locally analytic
distribution algebra of a compact -adic Lie group is finitely generated. In
particular, the category of coadmissible modules does not have enough
projectives. In the Appendix a "generalized Robba ring" for uniform pro-
groups is constructed which naturally contains the locally analytic
distribution algebra as a subring. The construction uses the theory of
generalized microlocalization of quasi-abelian normed algebras that is also
developed there. We equip this generalized Robba ring with a self-dual locally
convex topology extending the topology on the distribution algebra. This is
used to show some results on coadmissible modules.Comment: with an appendix by Peter Schneider; revised; new titl
Pressure and isotope effect on the anisotropy of MgB
We analyze the data for the pressure and boron isotope effect on the
temperature dependence of the magnetization near . Invoking the
universal scaling relation for the magnetization at fixed magnetic field it is
shown that the relative shift of , induced by pressure or boron isotope
exchange, mirrors essentially that of the anisotropy. This uncovers a novel
generic property of anisotropic type II superconductors, inexistent in the
isotropic case. For MgB it implies that the renormalization of the Fermi
surface topology due to pressure or isotope exchange is dominated by a
mechanism controlling the anisotropy.Comment: 7 pages, 3 figure
The z>4 Quasar Population Observed by Chandra and XMM-Newton
The current status of our Chandra and XMM-Newton project on high-redshift
(z>4) quasars is briefly reviewed. We report the main results obtained in the
last few years for the detected quasars, along with a few (~10%) intriguing
cases where no detection has been obtained with Chandra snapshot observations.Comment: 4 pages, to appear in the proceedings of 'Multiwavelength AGN
surveys' (Cozumel, December 8-12 2003), ed. R. Maiolino and R. Mujic
Constraining Dark Energy by Combining Cluster Counts and Shear-Shear Correlations in a Weak Lensing Survey
We study the potential of a large future weak-lensing survey to constrain
dark energy properties by using both the number counts of detected galaxy
clusters (sensitive primarily to density fluctuations on small scales) and
tomographic shear-shear correlations (restricted to large scales). We use the
Fisher matrix formalism, assume a flat universe and parameterize the equation
of state of dark energy by w(a)=w_0+w_a(1-a), to forecast the expected
statistical errors from either observable, and from their combination. We show
that the covariance between these two observables is small, and argue that
therefore they can be regarded as independent constraints. We find that when
the number counts and the shear-shear correlations (on angular scales l < 1000)
are combined, an LSST (Large Synoptic Survey Telescope)-like survey can yield
statistical errors on (Omega_DE, w_0, w_a) as tight as (0.003, 0.03, 0.1).
These values are a factor of 2-25 better than using either observable alone.
The results are also about a factor of two better than those from combining
number counts of galaxy clusters and their power spectrum.Comment: 17 pages, 5 figures, 10 tables, submitted to PR
Surface waves in protoplanetary disks induced by outbursts: Concentric rings in scattered light
Context: Vertically hydrostatic protoplanetary disk models are based on the
assumption that the main heating source, stellar irradiation, does not vary
much with time. However, it is known that accreting young stars are variable
sources of radiation. This is particularly evident for outbursting sources such
as EX Lupi and FU Orionis stars. Aim: We investigate how such outbursts affect
the vertical structure of the outer regions of the protoplanetary disk, in
particular their appearance in scattered light at optical and near-infrared
wavelengths. Methods: We employ the 3D FARGOCA radiation-hydrodynamics code, in
polar coordinates, to compute the time-dependent behavior of the axisymmetric
disk structure. The outbursting inner disk region is not included explicitly.
Instead, its luminosity is added to the stellar luminosity and is thus included
in the irradiation of the outer disk regions. For time snapshots of interest we
insert the density structure into the RADMC-3D radiative transfer code and
compute the appearance of the disk at optical/near-infrared wavelengths.
Results: We find that, depending on the amplitude of the outbursts, the
vertical structure of the disk can become highly dynamic, featuring circular
surface waves of considerable amplitude. These "hills" and "valleys" on the
disk's surface show up in the scattered light images as bright and dark
concentric rings. Initially these rings are small and act as standing waves,
but they subsequently lead to outward propagating waves, like the waves
produced by a stone thrown into a pond. These waves continue long after the
actual outburst has died out. Conclusions: We propose that some of the
multi-ringed structures seen in optical/infrared images of several
protoplanetary disks may have their origin in outbursts that occurred decades
or centuries ago.Comment: Accepted for publication in A&A Letter
Evidence for charged critical behavior in the pyrochlore superconductor RbOs2O6
We analyze magnetic penetration depth data of the recently discovered
superconducting pyrochlore oxide RbOs2O6. Our results strongly suggest that in
RbOs2O6 charged critical fuctuations dominate the temperature dependence of the
magnetic penetration depth near Tc. This is in contrast to the mean-field
behavior observed in conventional superconductors and the uncharged critical
behavior found in nearly optimally doped cuprate superconductors. However, this
finding agrees with the theoretical predictions for charged criticality and the
charged criticality observed in underdoped YBa2Cu3O6.59.Comment: 5 pages, 4 figure
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