756 research outputs found
Detection of Dark Matter Concentrations in the Field of Cl 1604+4304 from Weak Lensing Analysis
We present a weak-lensing analysis of a region around the galaxy cluster Cl
1604+4304 (z=0.897) on the basis of the deep observations with the HST/WFPC2.
We apply a variant of Schneider's aperture mass technique to the observed WFPC2
field and obtain the distribution of weak-lensing signal-to-noise (S/N) ratio
within the field. The resulting S/N map reveals a clear pronounced peak located
about 1.7 arcmin (850h_{50}^{-1} kpc at z=0.897) southwest of the second peak
associated with the optical cluster center determined from the dynamical
analysis of Postman et al. A non-linear finite-field inversion method has been
used to reconstruct the projected mass distribution from the observed shear
field. The reconstructed mass map shows a super-critical feature at the
location of the S/N peak as well as in the cluster central region. Assuming the
redshift distribution of field galaxies, we obtain the total mass in the
observed field to be 1.0 h_{50}^{-1} 10^{15} M_sun for =1.0. The estimated
mass within a circular aperture of radius 280h_{50}^{-1} kpc centered on the
dark clump is 2.4h_{50}^{-1} 10^{14} M_sun. We have confirmed the existence of
the ` dark ' mass concentration from another deep HST observation with a
slightly different ~20 arcsec pointing.Comment: 7 pages, 3 figure
Mass, Light and Colour of the Cosmic Web in the Supercluster SCL2243-0935 (z=0.447)
Context: In 2.2m MPG-ESO/WFI data we discovered several mass peaks through
weak lensing, forming a possible supercluster at redshift 0.45. Through
multi-colour wide-field imaging with CFHT/Megaprime and INT/WFC we identify
early-type galaxies and trace the supercluster network with them. Through
EMMI/NTT multi-object spectroscopy we verify the initial shear-selected cluster
candidates. Using weak lensing we obtain mass estimates for the supercluster
centre and the filaments.
Results: We identified the centre of the SCL2243-0935 supercluster, MACS
J2243-0935, which was found independently by Ebeling et al. (2010). 13 more
clusters or overdensities are embedded in a filamentary network, half of them
are already spectroscopically confirmed. Three (5-15) Mpc filaments are
detected, and we estimate the global size of SCL2243 to 45x15x50 Mpc, making it
one of the largest superclusters known at intermediate redshifts. Weak lensing
yields r_200=(2.06+/-0.13) Mpc and M_200=(1.54+/-0.29)x10^15 M_sun for MACS
J2243 with M/L=428+/-82, very similar to results from size-richness cluster
scaling relations. Integrating the weak lensing surface mass density over the
supercluster network (defined by increased i-band luminosity or g-i colours),
we find (1.53+/-1.01)x10^15 M_sun and M/L=305+/-201 for the three main
filaments, consistant with theoretical predictions. The filaments' projected
surface mass density is 0.007-0.012, corresponding to 10-100 times the critical
density. The greatly varying density of the cosmic web is also reflected in the
mean colour of galaxies. Conclusions: SCL2243 is significantly larger and much
more richly structured than other known superclusters such as A901/902 or
MS0302 studied with weak lensing before. It is a text-book supercluster with
little contamination along the line of sight, making it a perfect sandbox for
testing new techniques probing the cosmic web.Comment: 26 pages, 16 figures, accepted for publication Astronomy and
Astrophysics. Minor corrections implemented as requested by the refere
Lensing Magnification: A novel method to weigh high-redshift clusters and its application to SpARCS
We introduce a novel method to measure the masses of galaxy clusters at high
redshift selected from optical and IR Spitzer data via the red-sequence
technique. Lyman-break galaxies are used as a well understood, high-redshift
background sample allowing mass measurements of lenses at unprecedented high
redshifts using weak lensing magnification. By stacking a significant number of
clusters at different redshifts with average masses of ~1-3x10^14M_sun, as
estimated from their richness, we can calibrate the normalisation of the
mass-richness relation. With the current data set (area: 6 deg^2) we detect a
magnification signal at the >3-sigma level. There is good agreement between the
masses estimated from the richness of the clusters and the average masses
estimated from magnification, albeit with large uncertainties. We perform tests
that suggest the absence of strong systematic effects and support the
robustness of the measurement. This method - when applied to larger data sets
in the future - will yield an accurate calibration of the mass-observable
relations at z>~1 which will represent an invaluable input for cosmological
studies using the galaxy cluster mass function and astrophysical studies of
cluster formation. Furthermore this method will probably be the least expensive
way to measure masses of large numbers of z>1 clusters detected in future
IR-imaging surveys.Comment: 5 pages, 1 figure, 1 table, accepted by ApJL, minor revision
An optimal filter for the detection of galaxy clusters through weak lensing
We construct a linear filter optimised for detecting dark-matter halos in
weak-lensing data. The filter assumes a mean radial profile of the halo shear
pattern and modifies that shape by the noise power spectrum. Aiming at
separating dark-matter halos from spurious peaks caused by large-scale
structure lensing, we model the noise as being composed of weak lensing by
large-scale structures and Poisson noise from random galaxy positions and
intrinsic ellipticities. Optimal filtering against the noise requires the
optimal filter scale to be smaller than typical halo sizes. Although a perfect
separation of halos from spurious large-scale structure peaks is strictly
impossible, we use numerical simulations to demonstrate that our filter
produces substantially more sensitive, reliable and stable results than the
conventionally used aperture-mass statistic.Comment: 9 pages, 6 figures, A&A submitte
Testing the reliability of weak lensing cluster detections
We study the reliability of dark-matter halo detections with three different
linear filters applied to weak-lensing data. We use ray-tracing in the multiple
lens-plane approximation through a large cosmological simulation to construct
realizations of cosmic lensing by large-scale structures between redshifts zero
and two. We apply the filters mentioned above to detect peaks in the
weak-lensing signal and compare them with the true population of dark matter
halos present in the simulation. We confirm the stability and performance of a
filter optimized for suppressing the contamination by large-scale structure. It
allows the reliable detection of dark-matter halos with masses above a few
times 1e13 M_sun/h with a fraction of spurious detections below ~10%. For
sources at redshift two, 50% of the halos more massive than ~7e13 M_sun/h are
detected, and completeness is reached at ~2e14 M_sun/h.Comment: 14 pages, 13 figures, accepted on A&
Is Gravitational Lensing by Intercluster Filaments Always Negligible?
Intercluster filaments negligibly contribute to the weak lensing signal in
general relativity (GR), . In the context of
relativistic modified Newtonian dynamics (MOND) introduced by Bekenstein,
however, a single filament inclined by from the line of
sight can cause substantial distortion of background sources pointing towards
the filament's axis (); this is rigorous
for infinitely long uniform filaments, but also qualitatively true for short
filaments (Mpc), and even in regions where the projected matter
density of the filament is equal to zero. Since galaxies and galaxy clusters
are generally embedded in filaments or are projected on such structures, this
contribution complicates the interpretation of the weak lensing shear map in
the context of MOND. While our analysis is of mainly theoretical interest
providing order-of-magnitude estimates only, it seems safe to conclude that
when modeling systems with anomalous weak lensing signals, e.g. the "bullet
cluster" of Clowe et al., the "cosmic train wreck" of Abell 520 from Mahdavi et
al., and the "dark clusters" of Erben et al., filamentary structures might
contribute in a significant and likely complex fashion. On the other hand, our
predictions of a (conceptual) difference in the weak lensing signal could, in
principle, be used to falsify MOND/TeVeS and its variations.Comment: 11 pages, 6 figures, published versio
Bringing the circular economy home - Insights from socio-technical perspectives on everyday consumption
Transitions toward a circular economy require a nuanced understanding of how change plays out in households in relation to the role of consumers and daily consumption practices. However, little policy and research attention has been paid to the complexities of achieving necessary transformations in everyday cultures of consumption and the possible challenges faced by citizens and householders in achieving a circular economy. As a result, we know little about how circular consumption practices are already emerging in everyday life and can be scaled up across society. Additionally, critical gaps in understanding exist concerning how rebound and spillover effects occur in daily practices and the role of social and material contexts in configuring possibilities for circular consumption. Addressing these gaps, we develop an agenda for attending to the social embeddedness and complexity of participating in the circular economy. This agenda includes several critical elements, including the examination of routine and habitual aspects of social life, dynamics of rebound and spillover effects within interconnected practices, and the impact of institutional-material arrangements and provisioning systems on how consumers use services and products in the performance of social practices. In discussing these elements we outline research gaps and recommendations for future CE policy and research that better appreciates the social and material dynamics of everyday life, with the aim of addressing critical scientific and societal knowledge gaps concerning circular consumption transformations
Are transnational tobacco companies' market access strategies linked to economic development models? A case study of South Korea.
Transnational tobacco companies (TTCs) have used varied strategies to access previously closed markets. Using TTCs' efforts to enter the South Korean market from the late 1980s as a case study, this article asks whether there are common patterns in these strategies that relate to the broader economic development models adopted by targeted countries. An analytical review of the existing literature on TTCs' efforts to access emerging markets was conducted to develop hypotheses relating TTCs' strategies to countries' economic development models. A case study of Korea was then undertaken based on analysis of internal tobacco industry documents. Findings were consistent with the hypothesis that TTCs' strategies in Korea were linked to Korea's export-oriented economic development model and its hostile attitude towards foreign investment. A fuller understanding of TTCs' strategies for expansion globally can be derived by locating them within the economic development models of specific countries or regions. Of foremost importance is the need for governments to carefully balance economic and public health policies when considering liberalisation
GaBoDS: The Garching-Bonn Deep Survey: VII. Probing galaxy bias using weak gravitational lensing
[ABRIDGED] The weak gravitational lensing effect is used to infer matter
density fluctuations within the field-of-view of the Garching-Bonn Deep Survey
(GaBoDS). This information is employed for a statistical comparison of the
galaxy distribution to the total matter distribution. The result of this
comparison is expressed by means of the linear bias factor, b, the ratio of
density fluctuations, and the correlation factor between density
fluctuations. The total galaxy sample is divided into three sub-samples using
R-band magnitudes and the weak lensing analysis is applied separately for each
sub-sample. Together with the photometric redshifts from the related COMBO-17
survey we estimate the typical mean redshifts of these samples with
, respectively. For all three samples, a slight
galaxy anti-bias, b~0.8+-0.1, on scales of a few Mpc/h is found; the bias
factor shows evidence for a slight scale-dependence. The correlation between
galaxy and (dark) matter distribution is high, r~0.6+-0.2, indicating a
non-linear or/and stochastic biasing relation between matter and galaxies.
Between the three samples no significant evolution with redshift is found.Comment: 22 pages, 11 figures, LaTeX, accepted by A&A; estimates for the
uncertainties in the galaxy redshift distribution were added, new Section 4.4
on statistical errors in the galaxy bias calibration factor
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