478 research outputs found
ARCRAIDER I: Detailed optical and X-ray analysis of the cooling flow cluster Z3146
We present a detailed analysis of the medium redshift (z=0.2906) galaxy
cluster Z3146 which is part of the ongoing ARCRAIDER project, a systematic
search for gravitational arcs in massive clusters of galaxies. The analysis of
Z3146 is based on deep optical wide field observations in the B, V and R bands
obtained with the [email protected], and shallow archival WFPC2@HST taken with the
F606W filter, which are used for strong as well as weak lensing analyses.
Additionally we have used publicly available XMM/Newton observations for a
detailed X-ray analysis of Z3146. Both methods, lensing and X-ray, were used to
determine the dynamical state and to estimate the total mass. We also
identified four gravitational arc candidates. We find this cluster to be in a
relaxed state, which is confirmed by a large cooling flow with nominal
~1600M_\odot per year, regular galaxy density and light distributions and a
regular shape of the weak lensing mass reconstruction. The mass content derived
with the different methods agrees well within 25% at r_{200}=1661
h_{70}^{-1}kpc indicating a velocity dispersion of
\sigma_v=869^{+124}_{-153}km/s.Comment: accepted by A&A; 23 pages, 28 figures, 6 tables; High resolution
version can be found here:
http://astro.uibk.ac.at/~w.kausch/Z3146_astroph_hires.pdf.g
X-ray Diagnostics of Thermal Conditions of the Hot Plasmas in the Centaurus Cluster
X-ray data of the Centaurus cluster, obtained with {\it XMM-Newton} for 45
ksec, were analyzed. Deprojected EPIC spectra from concentric thin shell
regions were reproduced equally well by a single-phase plasma emission model,
or by a two-phase model developed by {\it ASCA}, both incorporating cool
(1.7--2.0 keV) and hot ( keV) plasma temperatures. However, EPIC
spectra with higher statistics, accumulated over 3-dimentional thick shell
regions, were reproduced better by the two-phase model than by the singe-phase
one. Therefore, hot and cool plasma phases are inferred to co-exist in the
cluster core region within kpc. The iron and silicon abundances of
the plasma were reconfirmed to increase significantly towards the center, while
that of oxygen was consistent with being radially constant. The implied
non-solar abundance ratios explains away the previously reported excess X-ray
absorption from the central region. Although an additional cool (
keV) emission was detected within kpc of the center, the RGS data
gave tight upper limits on any emission with a tempeartures below
keV. These results are compiled into a magnetosphere model, which interprets
the cool phase as confined within closed magnetic loops anchored to the cD
galaxy. When combined with so-called Rosner-Tucker-Vaiana mechanism which
applies to solar coronae, this model can potentially explain basic properties
of the cool phase, including its temperature and thermal stability.Comment: 53 pages, 11 figures, accepted for publication in Astrophysical
Journa
Ultraviolet Imaging Observations of the cD Galaxy in Abell 1795: Further Evidence for Massive Star Formation in a Cooling Flow
We present images from the Ultraviolet Imaging Telescope of the Abell 1795
cluster of galaxies. We compare the cD galaxy morphology and photometry of
these data with those from existing archival and published data. The addition
of a far--UV color helps us to construct and test star formation model
scenarios for the sources of UV emission. Models of star formation with rates
in the range \sim5-20M_{\sun}yr indicate that the best fitting models
are those with continuous star formation or a recent ( Myr old) burst
superimposed on an old population. The presence of dust in the galaxy,
dramatically revealed by HST images complicates the interpretation of UV data.
However, we find that the broad--band UV/optical colors of this cD galaxy can
be reasonably matched by models using a Galactic form for the extinction law
with . We also briefly discuss other objects in the large UIT
field of view.Comment: To appear in the Astrophysical Journal. 14 AAS preprint style pages
plus 7 figure
LoCuSS: First Results from Strong-lensing Analysis of 20 Massive Galaxy Clusters at z~0.2
We present a statistical analysis of a sample of 20 strong lensing clusters
drawn from the Local Cluster Substructure Survey (LoCuSS), based on high
resolution Hubble Space Telescope imaging of the cluster cores and follow-up
spectroscopic observations using the Keck-I telescope. We use detailed
parameterized models of the mass distribution in the cluster cores, to measure
the total cluster mass and fraction of that mass associated with substructures
within R<250kpc.These measurements are compared with the distribution of
baryons in the cores, as traced by the old stellar populations and the X-ray
emitting intracluster medium. Our main results include: (i) the distribution of
Einstein radii is log-normal, with a peak and 1sigma width of
=1.16+/-0.28; (ii) we detect an X-ray/lensing mass discrepancy of
=1.3 at 3 sigma significance -- clusters with larger substructure
fractions displaying greater mass discrepancies, and thus greater departures
from hydrostatic equilibrium; (iii) cluster substructure fraction is also
correlated with the slope of the gas density profile on small scales, implying
a connection between cluster-cluster mergers and gas cooling. Overall our
results are consistent with the view that cluster-cluster mergers play a
prominent role in shaping the properties of cluster cores, in particular
causing departures from hydrostatic equilibrium, and possibly disturbing cool
cores. Our results do not support recent claims that large Einstein radius
clusters present a challenge to the CDM paradigm.Comment: 28 pages, 14 figures, accepted for publication in MNRAS, replaced
with accepted versio
The changing of the guard: groupwork with people who have intellectual disabilities
This paper considers the impact of service systems on group activities. It describes an inter-professional groupwork project facilitated by a social worker and a community nurse. The project provided an emancipatory experience for a group of adults who had intellectual disabilities. The group was charged with the task of reviewing and updating the recruitment and interview processes used by a 'Learning Disability Partnership Board', when employing new support workers.
The paper begins with a brief history of intellectual disability and provides a context to the underpinning philosophical belief that people should be encouraged and supported to inhabit valued social roles no matter what disability they may have. It then identifies the ways in which the sponsoring health, education and social care services impacted on the creation and development of a groupwork project. It might have been expected that the nature of the intellectual disability would have been the major influence on group process. However the paper reveals that organisational constraints had a significant impact on group functioning. Issues including, staffing budgets and transport contracts impacted on group process and function.
The results of the project show how, with adequate support, people with intellectual disability can make important decisions that have long-reaching impacts on the services
LoCuSS: The mid-infrared Butcher-Oemler effect
We study the mid-infrared (MIR) properties of galaxies in 30 massive galaxy
clusters at 0.02<z<0.40, using panoramic Spitzer/MIPS 24micron and NIR data.
This is the largest sample of clusters to date with MIR data covering not only
the cluster cores, but extending into the infall regions. We revisit the
Butcher-Oemler effect, measuring the fraction of massive infrared-luminous
galaxies (K5x10^10L_sun) within r_200, finding a steady increase
in the fraction with redshift from ~3% at z=0.02 to ~10% by z=0.30, and an rms
cluster-to-cluster scatter about this trend of 0.03. The best-fit redshift
evolution model is of the form f_SF ~ (1+z)^5.7, which is stronger redshift
evolution than that of L*_IR in both clusters and the field. We find that,
statistically, this excess is associated with galaxies found at large
cluster-centric radii, implying that the MIR Butcher-Oemler effect can be
explained by a combination of both the global decline in star-formation in the
universe since z~1 and enhanced star formation in the infall regions of
clusters at intermediate redshifts. This picture is supported by a simple
infall model based on the Millennium Simulation semi-analytic galaxy catalogs,
whereby star-formation in infalling galaxies is instantaneously quenched upon
their first passage through the cluster, in that the observed radial trends of
f_SF trace those inferred from the simulations. We also find that f_SF does not
depend on simple indicators of the dynamical state of clusters, including the
offset between the brightest cluster galaxy and the peak of the X-ray emission.
This is consistent with the picture described above in that most new
star-formation in clusters occurs in the infall regions, and is thus not
sensitive to the details of cluster-cluster mergers in the core regions.Comment: 11 pages, 7 figures, accepted for publication in Ap
The XMM Cluster Survey: The interplay between the brightest cluster galaxy and the intra-cluster medium via AGN feedback
Using a sample of 123 X-ray clusters and groups drawn from the XMM-Cluster
Survey first data release, we investigate the interplay between the brightest
cluster galaxy (BCG), its black hole, and the intra-cluster/group medium (ICM).
It appears that for groups and clusters with a BCG likely to host significant
AGN feedback, gas cooling dominates in those with Tx > 2 keV while AGN feedback
dominates below. This may be understood through the sub-unity exponent found in
the scaling relation we derive between the BCG mass and cluster mass over the
halo mass range 10^13 < M500 < 10^15Msol and the lack of correlation between
radio luminosity and cluster mass, such that BCG AGN in groups can have
relatively more energetic influence on the ICM. The Lx - Tx relation for
systems with the most massive BCGs, or those with BCGs co-located with the peak
of the ICM emission, is steeper than that for those with the least massive and
most offset, which instead follows self-similarity. This is evidence that a
combination of central gas cooling and powerful, well fuelled AGN causes the
departure of the ICM from pure gravitational heating, with the steepened
relation crossing self-similarity at Tx = 2 keV. Importantly, regardless of
their black hole mass, BCGs are more likely to host radio-loud AGN if they are
in a massive cluster (Tx > 2 keV) and again co-located with an effective fuel
supply of dense, cooling gas. This demonstrates that the most massive black
holes appear to know more about their host cluster than they do about their
host galaxy. The results lead us to propose a physically motivated, empirical
definition of 'cluster' and 'group', delineated at 2 keV.Comment: Accepted for publication in MNRAS - replaced to match corrected proo
An X-ray Size-Temperature Relation for Galaxy Clusters: Observation and Simulation
We show that galaxy clusters conform to a tight relation between X-ray
isophotal size R_I and emission weighted intracluster medium (ICM) temperature
T_X. The best fit relation for 41 members of an X-ray flux limited cluster
sample is: ;
intrinsic scatter in size about the relation is 15%, and for 30 clusters with
T_X>4 keV the scatter is reduced to 10%. The existence of the size-temperature
(ST) relation indicates the ICM structure is a well behaved function of T_X. We
use an ensemble of gasdynamic simulations to demonstrate that a cluster
population experiencing present epoch growth nonetheless conforms to an ST
relation with scatter similar to that observed; the simulations also exhibit a
tight relation between M_{vir} and T_X, providing the suggestion that a similar
relation holds for observed clusters. We use the scatter in R_I to estimate
limits on the RMS variation in ICM mass fraction \delta f_{ICM} at constant
T_X: \delta f/f_{ICM}4 keV). It appears that a
mechanism like feedback from galaxy winds, which introduces systematic
structural changes in the ICM, is required to reproduce the observed slope of
the ST relation.Comment: Accepted for publication in ApJ, 9 pages Latex, 3 figure
Color-accurate underwater imaging using perceptual adaptive illumination
Capturing color in water is challenging due to the heavy non-uniform attenuation of light in water across the visible spectrum, which results in dramatic hue shifts toward blue. Yet observing color in water is important for monitoring and surveillance as well as marine biology studies related to species identification, individual and group behavior, and ecosystem health and activity monitoring. Underwater robots are equipped with motor control for large scale transects but they lack sensors that enable capturing color-accurate underwater images. We present a method for color-accurate imaging in water called perceptual adaptive illumination. This method dynamically mixes
the illumination of an object in a distance-dependent way using a controllable multi-color light source. The color mix compensates correctly for color loss and results in an image
whose color composition is equivalent to rendering the object in air. Experiments were conducted with a color palette in the pool and at three different coral reefs sites, and with an underwater
robot collecting image data with the new sensor.United States. Office of Naval Research (Project N000140911051
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The Patient and Carer Race Equality Framework: a model to reduce mental health inequity in England and Wales
The Patient and Carer Race Equality Framework (PCREF) is an Organisational Competence Framework (OCF), recommended by the Independent Review of the Mental Health Act as a means to improve mental health access, experience and outcomes for people from ethnic minority backgrounds, particularly Black people. This is a practical framework that should be co-produced with and tailored to the needs of service users, based on quality improvement and place-based approaches. We aim to use the PCREF to address the longstanding epistemic justices experienced by people with mental health problems, particularly those from minoritised ethnic groups. We will outline the work that led to the proposal, the research on racial inequalities in mental health in the UK, and how the PCREF will build on previous interventions to address these. By taking these into account, the PCREF should support a high minimum standard of mental health care for all
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