2,796 research outputs found
Next Generation Cosmology: Constraints from the Euclid Galaxy Cluster Survey
We study the characteristics of the galaxy cluster samples expected from the
European Space Agency's Euclid satellite and forecast constraints on
cosmological parameters describing a variety of cosmological models. The method
used in this paper, based on the Fisher Matrix approach, is the same one used
to provide the constraints presented in the Euclid Red Book (Laureijs et
al.2011). We describe the analytical approach to compute the selection function
of the photometric and spectroscopic cluster surveys. Based on the photometric
selection function, we forecast the constraints on a number of cosmological
parameter sets corresponding to different extensions of the standard LambdaCDM
model. The dynamical evolution of dark energy will be constrained to Delta
w_0=0.03 and Delta w_a=0.2 with free curvature Omega_k, resulting in a
(w_0,w_a) Figure of Merit (FoM) of 291. Including the Planck CMB covariance
matrix improves the constraints to Delta w_0=0.02, Delta w_a=0.07 and a
FoM=802. The amplitude of primordial non-Gaussianity, parametrised by f_NL,
will be constrained to \Delta f_NL ~ 6.6 for the local shape scenario, from
Euclid clusters alone. Using only Euclid clusters, the growth factor parameter
\gamma, which signals deviations from GR, will be constrained to Delta
\gamma=0.02, and the neutrino density parameter to Delta Omega_\nu=0.0013 (or
Delta \sum m_\nu=0.01). We emphasise that knowledge of the observable--mass
scaling relation will be crucial to constrain cosmological parameters from a
cluster catalogue. The Euclid mission will have a clear advantage in this
respect, thanks to its imaging and spectroscopic capabilities that will enable
internal mass calibration from weak lensing and the dynamics of cluster
galaxies. This information will be further complemented by wide-area
multi-wavelength external cluster surveys that will already be available when
Euclid flies. [Abridged]Comment: submitted to MNRA
The Evolution of K* and the Halo Occupation Distribution since z=1.5: Observations vs. Simulations
We study the evolution of the K-band luminosity function (LF) and the Halo
Occupation Distribution (HOD) using Subaru observations of 15 X-ray clusters at
z=0.8-1.5 and compare the results with mock clusters (0<z<1.3) extracted from
the Millennium Simulation and populated with galaxies using the semi-analytic
model (SAM) of Bower et al., matched in mass to our observed sample. We find
that the characteristic luminosity K* defined by a Shechter LF is consistent
with SAM predictions, which mimic well the evolution of K* in z>1 rich
clusters. However, we cannot distinguish between this model and a simple
stellar population synthesis model invoking passive evolution with a formation
redshift z~5 - consistent with the presence of an old red galaxy population
ubiquitous in rich clusters at z=1.5. We also see a small difference (\Delta
K*~0.5) between our clusters and studies of the field population at similar
redshifts, suggesting only a weak dependence of the luminous (L>L*) part of the
LF on environment. Turning to our HOD study, we find that within R_{500},
high-z clusters tend to host smaller numbers of galaxies to a magnitude K*+2
compared to their low-z counterparts. This behavior is also seen in the mock
samples and is relatively insensitive to the average mass of the cluster
haloes. In particular, we find significant correlations of the observed number
of member cluster galaxies (N) with both z and cluster mass:
.
Finally, we examine the spatial distribution of galaxies and provide a new
estimate of the concentration parameter for clusters at high z
(). Our result is consistent with predictions from
both our SAM mock clusters and literature's predictions for dark matter haloes.
The mock sample predictions rise slowly with decreasing redshift reaching
at z=0.Comment: 17 pages, 3 tables, 12 Figures. Accepted for publications in MNRAS.
Version 2: modified Figs. 4, 8 and 1
Seismic moment tensor results for nine events in the North Korea region
We determine moment tensor solutions for nine events in the North Korea region. This is a supplement for a published manuscript by Alvizuri and Tape (2018).This project was supported in part by the Swiss National Science Foundation (grant PP00P2_157627: OROG3NY) and by the U.S. Air Force Research Laboratory (contract FA9453-17-C-0025)
Velocities from Cross-Correlation: A Guide for Self-Improvement
The measurement of Doppler velocity shifts in spectra is a ubiquitous theme
in astronomy, usually handled by computing the cross-correlation of the
signals, and finding the location of its maximum. This paper addresses the
problem of the determination of wavelength or velocity shifts among multiple
spectra of the same, or very similar, objects. We implement the classical
cross-correlation method and experiment with several simple models to determine
the location of the maximum of the cross-correlation function. We propose a new
technique, 'self-improvement', to refine the derived solutions by requiring
that the relative velocity for any given pair of spectra is consistent with all
others. By exploiting all available information, spectroscopic surveys
involving large numbers of similar objects may improve their precision
significantly. As an example, we simulate the analysis of a survey of G-type
stars with the SDSS instrumentation. Applying 'self-improvement' refines
relative radial velocities by more than 50% at low signal-to-noise ratio. The
concept is equally applicable to the problem of combining a series of
spectroscopic observations of the same object, each with a different Doppler
velocity or instrument-related offset, into a single spectrum with an enhanced
signal-to-noise ratio.Comment: 7 pages, 3 figures, uses emulateapj.cls; to appear in the
Astronomical Journal; see http://hebe.as.utexas.edu/stools/ to obtain the
companion softwar
The XXL Survey X: K-band luminosity - weak-lensing mass relation for groups and clusters of galaxies
We present the K-band luminosity-halo mass relation, ,
for a subsample of 20 of the 100 brightest clusters in the XXL Survey observed
with WIRCam at the Canada-France-Hawaii Telescope (CFHT). For the first time,
we have measured this relation via weak-lensing analysis down to . This allows us to investigate whether the slope
of the relation is different for groups and clusters, as seen in other
works. The clusters in our sample span a wide range in mass, , at . The K-band luminosity
scales as with and an
intrinsic scatter of . Combining our
sample with some clusters in the Local Cluster Substructure Survey (LoCuSS)
present in the literature, we obtain a slope of and an
intrinsic scatter of . The flattening in the seen
in previous works is not seen here and might be a result of a bias in the mass
measurement due to assumptions on the dynamical state of the systems. We also
study the richness-mass relation and find that group-sized halos have more
galaxies per unit halo mass than massive clusters. However, the brightest
cluster galaxy (BCG) in low-mass systems contributes a greater fraction to the
total cluster light than BCGs do in massive clusters; the luminosity gap
between the two brightest galaxies is more prominent for group-sized halos.
This result is a natural outcome of the hierarchical growth of structures,
where massive galaxies form and gain mass within low-mass groups and are
ultimately accreted into more massive clusters to become either part of the BCG
or one of the brighter galaxies. [Abridged]Comment: A&A, in pres
Searching for galaxy clusters in the Kilo-Degree Survey
In this paper, we present the tools used to search for galaxy clusters in the
Kilo Degree Survey (KiDS), and our first results. The cluster detection is
based on an implementation of the optimal filtering technique that enables us
to identify clusters as over-densities in the distribution of galaxies using
their positions on the sky, magnitudes, and photometric redshifts. The
contamination and completeness of the cluster catalog are derived using mock
catalogs based on the data themselves. The optimal signal to noise threshold
for the cluster detection is obtained by randomizing the galaxy positions and
selecting the value that produces a contamination of less than 20%. Starting
from a subset of clusters detected with high significance at low redshifts, we
shift them to higher redshifts to estimate the completeness as a function of
redshift: the average completeness is ~ 85%. An estimate of the mass of the
clusters is derived using the richness as a proxy. We obtained 1858 candidate
clusters with redshift 0 < z_c < 0.7 and mass 13.5 < log(M500/Msun) < 15 in an
area of 114 sq. degrees (KiDS ESO-DR2). A comparison with publicly available
Sloan Digital Sky Survey (SDSS)-based cluster catalogs shows that we match more
than 50% of the clusters (77% in the case of the redMaPPer catalog). We also
cross-matched our cluster catalog with the Abell clusters, and clusters found
by XMM and in the Planck-SZ survey; however, only a small number of them lie
inside the KiDS area currently available.Comment: 13 pages, 15 figures. Accepted for publication on Astronomy &
Astrophysic
Statistical investigation of fatigue crack initiation and growth around chamfered rivet holes in Alclad 2024 T3 as affected by corrosion
In panel specimens with rivet holes cracks initiate in the blunted knife edge of the chamfered rivet hole and propagate inward as well as along the hole. The fatigue lifetime to dominant crack information was defined as the number of cycles, N500 micrometer, to formation of a 500 micrometer long crack. Statistical data on N500 micrometer and on crack propagation after N500 micrometer were obtained for a large number of uncorroded specimens and specimens corroded in an ASTM B 117 salt spray. Considerable variation in N500 micrometer and crack propagation behavior was observed from specimen to specimen of the same nominal geometry with chamfered rivet holes increased the probability for both early formation and later formation of a propagating 500 micrometer fatigue crack. The growth of fatigue cracks after 500 micrometer size was little affected by prior salt spray
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