386 research outputs found
Projection effects in galaxy cluster samples: insights from X-ray redshifts
Up to now, the largest sample of galaxy clusters selected in X-rays comes
from the ROSAT All-Sky Survey (RASS). Although there have been many interesting
clusters discovered with the RASS data, the broad point spread function (PSF)
of the ROSAT satellite limits the amount of spatial information of the detected
objects. This leads to the discovery of new cluster features when a
re-observation is performed with higher resolution X-ray satellites. Here we
present the results from XMM-Newton observations of three clusters:
RXCJ2306.6-1319, ZwCl1665 and RXCJ0034.6-0208, for which the observations
reveal a double or triple system of extended components. These clusters belong
to the extremely expanded HIghest X-ray FLUx Galaxy Cluster Sample
(eeHIFLUGCS), which is a flux-limited cluster sample ( erg s cm in the keV energy band). For
each structure in each cluster, we determine the redshift with the X-ray
spectrum and find that the components are not part of the same cluster. This is
confirmed by an optical spectroscopic analysis of the galaxy members.
Therefore, the total number of clusters is actually 7 and not 3. We derive
global cluster properties of each extended component. We compare the measured
properties to lower-redshift group samples, and find a good agreement. Our flux
measurements reveal that only one component of the ZwCl1665 cluster has a flux
above the eeHIFLUGCS limit, while the other clusters will no longer be part of
the sample. These examples demonstrate that cluster-cluster projections can
bias X-ray cluster catalogues and that with high-resolution X-ray follow-up
this bias can be corrected
The XXL Survey VIII: MUSE characterisation of intracluster light in a z0.53 cluster of galaxies
Within a cluster, gravitational effects can lead to the removal of stars from
their parent galaxies. Gas hydrodynamical effects can additionally strip gas
and dust from galaxies. The properties of the ICL can therefore help constrain
the physical processes at work in clusters by serving as a fossil record of the
interaction history. The present study is designed to characterise this ICL in
a ~10^14 M_odot and z~0.53 cluster of galaxies from imaging and spectroscopic
points of view. By applying a wavelet-based method to CFHT Megacam and WIRCAM
images, we detect significant quantities of diffuse light. These sources were
then spectroscopically characterised with MUSE. MUSE data were also used to
compute redshifts of 24 cluster galaxies and search for cluster substructures.
An atypically large amount of ICL has been detected in this cluster. Part of
the detected diffuse light has a very weak optical stellar component and
apparently consists mainly of gas emission, while other diffuse light sources
are clearly dominated by old stars. Furthermore, emission lines were detected
in several places of diffuse light. Our spectral analysis shows that this
emission likely originates from low-excitation parameter gas. The stellar
contribution to the ICL is about 2.3x10^9 yrs old even though the ICL is not
currently forming a large number of stars. On the other hand, the contribution
of the gas emission to the ICL in the optical is much greater than the stellar
contribution in some regions, but the gas density is likely too low to form
stars. These observations favour ram pressure stripping, turbulent viscous
stripping, or supernovae winds as the origin of the large amount of
intracluster light. Since the cluster appears not to be in a major merging
phase, we conclude that ram pressure stripping is the most plausible process
that generates the observed ICL sources.Comment: Accepted in A&A, english enhanced, figure location different than in
the A&A version due to different style files, shortened abstrac
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
The 2-10 keV unabsorbed luminosity function of AGN from the XMM-Newton LSS, CDFS and COSMOS surveys
The XMM-LSS, XMM-COSMOS, and XMM-CDFS surveys are complementary in terms of
sky coverage and depth. Together, they form a clean sample with the least
possible variance in instrument effective areas and PSF. Therefore this is one
of the best samples available to determine the 2-10 keV luminosity function of
AGN and its evolution. The samples and the relevant corrections for
incompleteness are described. A total of 2887 AGN is used to build the LF in
the luminosity interval 10^42-10^46 erg/s, and in the redshift interval
0.001-4. A new method to correct for absorption by considering the probability
distribution for the column density conditioned on the hardness ratio is
presented. The binned luminosity function and its evolution is determined with
a variant of the Page-Carrera method, improved to include corrections for
absorption and to account for the full probability distribution of photometric
redshifts. Parametric models, namely a double power-law with LADE or LDDE
evolution, are explored using Bayesian inference. We introduce the
Watanabe-Akaike information criterion (WAIC) to compare the models and estimate
their predictive power. Our data are best described by the LADE model, as
hinted by the WAIC indicator. We also explore the 15-parameter extended LDDE
model recently proposed by Ueda et al., and find that this extension is not
supported by our data. The strength of our method is that it provides:
un-absorbed non-parametric estimates; credible intervals for luminosity
function parameters; model choice according to which one has more predictive
power for future data.Comment: In press on A&A. The revised version corrects typos and the LF
normalisations in tables 1,2,5 and figs.9-12, which were on an incorrect
scale. Online material available at
http://www.astro.lu.se/~piero/xlf/xlf-paper-tables2.tgz . The software is
available on the author's website
http://www.astro.lu.se/~piero/LFTools/index.html and on github:
https://github.com/piero-ranalli/LFTool
Effect of the microstructure on the cutting performance of superhard (Ti, Si, Al)N nanocomposite films
A d.c. reactive magnetron sputtering technique was used to deposit (Ti,Si,Al)N coatings onto WC–Co
cutting tools. The microstructure of the coatings was analysed using X-ray diffraction (XRD) and highresolution
transmission electron microscopy (HRTEM) measurement. Before the cutting experiments, the
XRD results revealed a structure indexed to an fcc TiN. The results obtained by the XRD tests, with
detector variation in asymmetric mode (rocking curves) showed a decrease in the quality of the fiber
texture in the (111) grains with the change on deposition chamber geometry (two magnetrons in place of
four magnetrons). Cross-sectional HRTEM images of the (Ti,Al)N sample showed grains with a diameter
between 16 and 30 nm, while for the (Ti,Si,Al)N samples grains with a diameter between 6 and 10 nm
were observed. Furthermore, through the visualization of bright field images it was possible to discern
a columnar structure. For samples prepared at high deposition rates (2 mm/h), HRTEM micrographs
revealed the formation of the multilayer stacking of (Ti,Si)N/(Ti,Al)N
Structural analysis of Ti1−xSixNy nanocomposite films prepared by reactive magnetron sputtering
Nanocomposite thin films consisting of both nanosized solid solutions or nanosized polycrystalline materials embedded in various amorphous matrix materials thus provide a grate potential for future mechanical devices. In this paper we report on the preparation of films resulting from additions of Si to TiN matrix by r.f. reactive magnetron sputtering. Structural properties such as growing characteristics (type of matrix, texture and grain size) will be analysed in some detail. Conventional transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM), together with both symmetric and asymmetric mode X-ray diffraction (XRD) experiments were used for this characterisation. The atomic composition of the samples was obtained by Rutherford Backscattering Spectrometry (RBS).
The analysis will be carried out as a function of the Si content in the Ti1-xSixNy matrix and several relations will be made regarding important parameters such as texture evolution, grain sizes, but most specially by the type of matrix developed. Regarding the results, all samples develop a double fcc phase with lattice parameters of 4.30 Å and 4.17 Å, corresponding to cubic TiN and most likely to a cubic lattice of SiNx, respectively.
Although no significant changes in texture were observed till Si compositions up to 10.6 at. %, the arrangement in atoms planes seem to vary. Results show that an asymmetric arrangement is developed in samples of small Si additions. This arrangement becomes more isotropic with the increase of Si contents, which we attribute to the increase in the SiNx content. In fact this increase leads also to the development of a small amorphous tissue of Si3N4 for large Si additions.The authors gratefully acknowledge the financial support of the ‘Fundação para a Ciência e Tecnologia’ (FCT) during the course of this research under project n PBICT/P/CTM/1962/95 and also the French CNRS Institution and the Portugese ICCTI Institution through CNRS/ICCTI Programs (N: 5522-1998 and 7087-1999)
The XXL Survey VII: A supercluster of galaxies at z=0.43
The XXL Survey is the largest homogeneous and contiguous survey carried out
with XMM-Newton. Covering an area of 50 square degrees distributed over two
fields, it primarily investigates the large-scale structures of the Universe
using the distribution of galaxy clusters and active galactic nuclei as tracers
of the matter distribution. Given its depth and sky coverage, XXL is
particularly suited to systematically unveiling the clustering of X-ray
clusters and to identifying superstructures in a homogeneous X-ray sample down
to the typical mass scale of a local massive cluster. A friends-of-friends
algorithm in three-dimensional physical space was run to identify large-scale
structures. In this paper we report the discovery of the highest redshift
supercluster of galaxies found in the XXL Survey. We describe the X-ray
properties of the clusters members of the structure and the optical follow-up.
The newly discovered supercluster is composed of six clusters of galaxies at a
median redshift z around 0.43 and distributed across approximately 30 by 15 arc
minutes (10 by 5 Mpc on sky) on the sky. This structure is very compact with
all the clusters residing in one XMM pointing; for this reason this is the
first supercluster discovered with the XXL Survey. Spectroscopic follow-up with
WHT (William Herschel Telescope) and NTT (New Technology Telescope) confirmed a
median redshift of z = 0.43. An estimate of the X-ray mass and luminosity of
this supercluster and of its total gas mass put XLSSC-e at the average mass
range of superclusters; its appearance, with two members of equal size, is
quite unusual with respect to other superclusters and provides a unique view of
the formation process of a massive structure.Comment: A&A, accepted; special XXL issu
The XXL Survey XI: ATCA 2.1 GHz continuum observations
We present 2.1 GHz imaging with the Australia Telescope Compact Array (ATCA)
of a 6.5 deg^2 region within the XXM-Newton XXL South field using a band of
1.1-3.1 GHz. We achieve an angular resolution of 4.7" x 4.2" in the final radio
continuum map with a median rms noise level of 50 uJy/beam. We identify 1389
radio sources in the field with peak S/N >=5 and present the catalogue of
observed parameters. We find that 305 sources are resolved, of which 77 consist
of multiple radio components. These number counts are in agreement with those
found for the COSMOS-VLA 1.4 GHz survey. We derive spectral indices by a
comparison with the Sydney University Molongolo Sky Survey (SUMSS) 843MHz data.
We find an average spectral index of -0.78 and a scatter of 0.28, in line with
expectations. This pilot survey was conducted in preparation for a larger ATCA
program to observe the full 25 deg^2 southern XXL field. When complete, the
survey will provide a unique resource of sensitive, wide-field radio continuum
imaging with complementary X-ray data in the field. This will facilitate
studies of the physical mechanisms of radio-loud and radio-quiet AGNs and
galaxy clusters, and the role they play in galaxy evolution. The source
catalogue is publicly available online via the XXL Master Catalogue browser and
the Centre de Donn\'ees astronomiques de Strasbourg (CDS).Comment: 7 pages, 6 figures. Accepted by A&A 13th October 201
The Spitzer-South Pole Telescope Deep Field: Survey Design and IRAC Catalogs
The Spitzer-South Pole Telescope Deep Field (SSDF) is a wide-area survey
using Spitzer's Infrared Array Camera (IRAC) to cover 94 square degrees of
extragalactic sky, making it the largest IRAC survey completed to date outside
the Milky Way midplane. The SSDF is centered at 23:30,-55:00, in a region that
combines observations spanning a broad wavelength range from numerous
facilities. These include millimeter imaging from the South Pole Telescope,
far-infrared observations from Herschel/SPIRE, X-ray observations from the XMM
XXL survey, near-infrared observations from the VISTA Hemisphere Survey, and
radio-wavelength imaging from the Australia Telescope Compact Array, in a
panchromatic project designed to address major outstanding questions
surrounding galaxy clusters and the baryon budget. Here we describe the
Spitzer/IRAC observations of the SSDF, including the survey design,
observations, processing, source extraction, and publicly available data
products. In particular, we present two band-merged catalogs, one for each of
the two warm IRAC selection bands. They contain roughly 5.5 and 3.7 million
distinct sources, the vast majority of which are galaxies, down to the SSDF
5-sigma sensitivity limits of 19.0 and 18.2 Vega mag (7.0 and 9.4 microJy) at
3.6 and 4.5 microns, respectively.Comment: Accepted by ApJS; this version updated to conform to refereed articl
Combined analysis of weak lensing and X-ray blind surveys
We present a joint weak lensing and X-ray analysis of 4 deg from the
CFHTLS and XMM-LSS surveys. Our weak lensing analysis is the first analysis of
a real survey using shapelets, a new generation weak lensing analysis method.
We create projected mass maps of the images, and extract 6
weak-lensing-detected clusters of galaxies. We show that their counts can be
used to constrain the power spectrum normalisation for . We show that despite the large
scatter generally observed in the M-T relation derived from lensing masses,
tight constraints on both its slope and normalisation can be obtained
with a moderate number of sources provided that the covered mass range is large
enough. Adding clusters from Bardeau et al. (2007) to our sample, we measure
. Although they are
dominated by shot noise and sample variance, our measurements are consistent
with currently favoured values, and set the stage for future surveys. We thus
investigate the dependence of those estimates on survey size, depth, and
integration time, for joint weak lensing and X-ray surveys. We show that deep
surveys should be dedicated to the study of the physics of clusters and groups
of galaxies. For a given exposure time, wide surveys provide a larger number of
detected clusters and are therefore preferred for the measurement of
cosmological parameters such as and . We show that a wide
survey of a few hundred square degrees is needed to improve upon current
measurements of these parameters. More ambitious surveys covering 7000 deg
will provide the 1% accuracy in the estimation of the power spectrum and the
M-T relation normalisations.Comment: MNRAS in press Matches accepted version. References update
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