866 research outputs found
The 3D soft X-ray cluster-AGN cross-correlation function in the ROSAT NEP survey
X-ray surveys facilitate investigations of the environment of AGNs. Deep
Chandra observations revealed that the AGNs source surface density rises near
clusters of galaxies. The natural extension of these works is the measurement
of spatial clustering of AGNs around clusters and the investigation of relative
biasing between active galactic nuclei and galaxies near clusters.The major
aims of this work are to obtain a measurement of the correlation length of AGNs
around clusters and a measure of the averaged clustering properties of a
complete sample of AGNs in dense environments. We present the first measurement
of the soft X-ray cluster-AGN cross-correlation function in redshift space
using the data of the ROSAT-NEP survey. The survey covers 9x9 deg^2 around the
North Ecliptic Pole where 442 X-ray sources were detected and almost completely
spectroscopically identified. We detected a >3sigma significant clustering
signal on scales s<50 h70^-1 Mpc. We performed a classical maximum-likelihood
power-law fit to the data and obtained a correlation length s_0=8.7+1.2-0.3
h_70-1 Mpc and a slope gamma=1.7$^+0.2_-0.7 (1sigma errors). This is a strong
evidence that AGNs are good tracers of the large scale structure of the
Universe. Our data were compared to the results obtained by cross-correlating
X-ray clusters and galaxies. We observe, with a large uncertainty, that the
bias factor of AGN is similar to that of galaxies.Comment: 4 pages, 2 figure, proceedings of the Conference "At the edge of the
Universe", Sintra Portugal, October 2006. To be published on the Astronomical
Society of the Pacific Conference Series (ASPCS
Literacy practices of primary education children in Andalusia (Spain): a family-based perspective
Primary school children develop literacy practices in various domains and situations in everyday life.
This study focused on the analysis of literacy practices of children aged 8â12 years from the perspec-
tive of their families. 1,843 families participated in the non-experimental explanatory study. The
children in these families speak Spanish as a first language and are schooled in this language. The
instrument used was a self-report questionnaire about childrenâs home-literacy practices. The data
obtained were analysed using categorical principal components analysis (CATPCA) and analysis of
variance (ANOVA). The results show the complex relationship between literacy practices developed
by children in the domains of home and school and the limited development of a literacy-promoting
âthird spaceâ. In conclusion, the families in our study had limited awareness of their role as literacy-
promoting agents and thought of literacy learning as restricted to formal or academic spaces
Insulin increases serum leptin concentrations in children and adolescents with newly diagnosed Type I diabetes mellitus with and without ketoacidosis
Redshift Evolution in the Iron Abundance of the Intracluster Medium
Clusters of galaxies provide a closed box within which one can determine the
chemical evolution of the gaseous baryons with cosmic time. We studied this
metallicity evolution in the hot X-ray emitting baryons through an analysis of
XMM-Newton observations of 29 galaxy clusters in the redshift range 0.3 < z <
1.3. Taken alone, this data set does not show evidence for significant
evolution. However, when we also include a comparable sample of 115 clusters
observed with Chandra (Maughan et al. 2008) and a lower redshift sample of 70
clusters observed with XMM at z < 0.3 (Snowden et al. 2008), there is
definitive evidence for a decrease in the metallicity. This decrease is
approximately a factor of two from z = 0 to z \approx 1, over which we find a
least-squares best-fit line Z(z) / Z_{\odot} = (0.46 \pm 0.05) - (0.38 \pm
0.03)z. The greatest uncertainty in the evolution comes from poorly constrained
metallicities in the highest redshift bin
Simulations of three-dimensional dendritic growth using a coupled thermo-solutal phase-field model
Using a phase field model, which fully couples the thermal and solute concentration field, we present simulation results in three dimensions of the rapid dendritic solidification of a class of dilute alloys at the meso scale. The key results are the prediction of steady state tip velocity and radius at varying undercooling and thermal diffusivities. Less computationally demanding 2-dimensional results are directly compared with the corresponding 3-dimensional results, where significant quantitative differences emerge. The simulations provide quantitative predictions for the range of thermal and solutal diffusivities considered and show the effectiveness and potential of the computational techniques employed. These results thus provide benchmark 3-dimensional computations, allow direct comparison with underlying analytical theory, and pave the way for further quantitative results
The WARPS survey: III. The discovery of an X-ray luminous galaxy cluster at z=0.833 and the impact of X-ray substructure on cluster abundance measurements
The WARPS team reviews the properties and history of discovery of
ClJ0152.7-1357, an X-ray luminous, rich cluster of galaxies at z=0.833. At L_X
= 8 x 10^44 h^(-2) erg/s (0.5-2.0 keV) ClJ0152.7-1357 is the most X-ray
luminous cluster known at redshifts z>0.55. The high X-ray luminosity of the
system suggests that massive clusters may begin to form at redshifts
considerably greater than unity. This scenario is supported by the high degree
of optical and X-ray substructure in ClJ0152.7-1357, which is similarly complex
as that of other X-ray selected distant clusters and consistent with the
picture of cluster formation by mass infall along large-scale filaments. X-ray
emission from ClJ0152.7-1357 was detected already in 1980 with the EINSTEIN
IPC. However, because the complex morphology of the emission caused its
significance to be underestimated, the corresponding source was not included in
the EMSS cluster sample and hence not previously identified. Simulations of the
EMSS source detection and selection procedure suggest a general bias of the
EMSS against X-ray luminous clusters with pronounced substructure. If highly
unrelaxed, merging clusters are common at high redshift, they could create a
bias in some samples as the morphological complexity of mergers may cause them
to fall below the flux limit of surveys that assume a unimodal spatial source
geometry. Conversely, the enhanced X-ray luminosity of mergers might cause them
to, temporarily, rise above the flux limit. Either effect could lead to
erroneous conclusions about the evolution of the comoving cluster space
density. A high fraction of morphologically complex clusters at high redshift
would also call into question the validity of cosmological studies that assume
that the systems under investigation are virialized.Comment: 17 pages, 7 figures; revised to focus on possible detection biases
caused by substructure in clusters; accepted for publication in ApJ; uses
emulateapj.sty; eps files of figures 1 and 2 can be obtained from
ftp://hubble.ifa.hawaii.edu/pub/ebeling/warp
The soft X-ray Cluster-AGN spatial cross-correlation function in the ROSAT-NEP survey
X-ray surveys facilitate investigations of the environment of AGNs. Deep
Chandra observations revealed that the AGNs source surface density rises near
clusters of galaxies. The natural extension of these works is the measurement
of spatial clustering of AGNs around clusters and the investigation of relative
biasing between active galactic nuclei and galaxies near clusters. The major
aims of this work are to obtain a measurement of the correlation length of AGNs
around clusters and a measure of the averaged clustering properties of a
complete sample of AGNs in dense environments. We present the first measurement
of the soft X-ray cluster-AGN cross-correlation function in redshift space
using the data of the ROSAT-NEP survey. The survey covers 9x9 deg^2 around the
North Ecliptic Pole where 442 X-ray sources were detected and almost completely
spectroscopically identified. We detected a > 3 sigma significant clustering
signal on scales s<50 h_70^-1 Mpc. We performed a classical maximum-likelihood
power-law fit to the data and obtained a correlation length s_0=8.7^+1.2_-0.3
h70^-1 Mpc and a slope gamma=1.7^+0.2_-0.7 (1 sigma errors). This is a strong
evidence that AGNs are good tracers of the large scale structure of the
Universe. Our data were compared to the results obtained by cross-correlating
X-ray clusters and galaxies. We observe, with a large uncertainty, a similar
behaviour of the AGNs clustering around clusters similar to the clustering of
galaxies around clusters.Comment: 7 pages, 6 figures, Accepted by A&
An S-shaped arc in the galaxy cluster RXJ0054.0-2823
The center of the galaxy cluster RX J0054.0-2823 at z = 0.292 is a
dynamically active region which includes an interacting system of three
galaxies surrounded by a large halo of intra-cluster light. We report here the
discovery of an S-shaped feature of total length 11 arcsec in the central
region of this cluster and discuss its physical nature. We test the
gravitational lensing assumption by doing a mass modelling of the central part
of the galaxy cluster. We very naturally reproduce position and form of this
S-shape feature as a gravitationally lensed background object at redshift
between 0.5 and 1.0. We conclude that the lensing nature is the very probable
explanation for this S-shaped arc; the ultimate proof will be the spectroscopic
confirmation by measuring the high redshift of this elongated feature with
surface brightness V~24mag/arcsec2.Comment: 6 pages, accepted for publication in A&
Discovery of an X-ray-Luminous Galaxy Cluster at z=1.4
We report the discovery of a massive, X-ray-luminous cluster of galaxies at
z=1.393, the most distant X-ray-selected cluster found to date. XMMU
J2235.3-2557 was serendipitously detected as an extended X-ray source in an
archival XMM-Newton observation of NGC 7314. VLT-FORS2 R and z band snapshot
imaging reveals an over-density of red galaxies in both angular and color
spaces. The galaxy enhancement is coincident in the sky with the X-ray
emission; the cluster red sequence at R-z ~ 2.1 identifies it as a
high-redshift candidate. Subsequent VLT-FORS2 multi-object spectroscopy
unambiguously confirms the presence of a massive cluster based on 12 concordant
redshifts in the interval 1.38<z<1.40. The preliminary cluster velocity
dispersion is 762+/-265 km/s. VLT-ISAAC Ks and J band images underscore the
rich distribution of red galaxies associated with the cluster. Based on a 45 ks
XMM-Newton observation, we find the cluster has an aperture-corrected,
unabsorbed X-ray flux of f_X = (3.6 +/- 0.3) x 10^{-14} erg/cm^2/s, a
rest-frame X-ray luminosity of L_X = (3.0 +/- 0.2) x 10^{44} h_70^{-2} erg/s
(0.5--2.0 keV), and a temperature of kT=6.0 (+2.5, -1.8) keV. Though XMMU
J2235.3-2557 is likely the first confirmed z>1 cluster found with XMM-Newton,
the relative ease and efficiency of discovery demonstrates that it should be
possible to build large samples of z>1 clusters through the joint use of X-ray
and large, ground-based telescopes.Comment: 4 pages, 3 figures, accepted for publication in ApJ Letters, a
high-resolution version is available at
http://www.astro.lsa.umich.edu/~cmullis/papers/Mullis_et_al_2005a.pdf,
additional information is available at
http://www.astro.lsa.umich.edu/~cmullis/research/xmmuj223
RXJ1716.6+6708: a young cluster at z=0.81
Clusters of galaxies at redshifts nearing one are of special importance since
they may be caught at the epoch of formation. At these high redshifts there are
very few known clusters. We present follow-up ASCA, ROSAT HRI and Keck LRIS
observations of the cluster RXJ1716.6+6708 which was discovered during the
optical identification of X-ray sources in the North Ecliptic Pole region of
the ROSAT All-Sky Survey. At z=0.809, RXJ1716.6+6708 is the second most distant
X-ray selected cluster so far published and the only one with a large number of
spectroscopically determined cluster member velocities. The optical morphology
of RXJ1716.6+6708 resembles an inverted S-shape filament with the X-rays coming
from the midpoint of the filament. The X-ray contours have an elongated shape
that roughly coincide with the weak lensing contours. The cluster has a low
temperature, kT=5.66{+1.37 -0.58} keV, and a very high velocity dispersion
sigma_{los}=1522{+215 -150} km s^{-1}. While the temperature is commensurate
with its X-ray luminosity of (8.19 +/- 0.43)x10^{44} h_{50}^{-2} erg s^{-1}
(2-10 keV rest frame), its velocity dispersion is much higher than expected
from the sigma-T_X relationship of present-day clusters with comparable X-ray
luminosity. RXJ1716.6+6708 could be an example of a protocluster, where matter
is flowing along filaments and the X-ray flux is maximum at the impact point of
the colliding streams of matter.Comment: Latex file, 18 pages, 4 figures, accepted for publication in the
Astronomical Journa
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