546 research outputs found
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
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
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
The-wiZZ: Clustering redshift estimation for everyone
We present The-wiZZ, an open source and user-friendly software for estimating the redshift distributions of photometric galaxies with unknown redshifts by spatially cross-correlating them against a reference sample with known redshifts. The main benefit of The-wiZZ is in separating the angular pair finding and correlation estimation from the computation of the output clustering redshifts allowing anyone to create a clustering redshift for their sample without the intervention of an "expert". It allows the end user of a given survey to select any sub-sample of photometric galaxies with unknown redshifts, match this sample's catalog indices into a value-added data file, and produce a clustering redshift estimation for this sample in a fraction of the time it would take to run all the angular correlations needed to produce a clustering redshift. We show results with this software using photometric data from the Kilo-Degree Survey (KiDS) and spectroscopic redshifts from the Galaxy and Mass Assembly (GAMA) survey and the Sloan Digital Sky Survey (SDSS). The results we present for KiDS are consistent with the redshift distributions used in a recent cosmic shear analysis from the survey. We also present results using a hybrid machine learning-clustering redshift analysis that enables the estimation of clustering redshifts for individual galaxies. The-wiZZ can be downloaded at http://github.com/morriscb/The-wiZZ/
KiDS-i-800: Comparing weak gravitational lensing measurements in same-sky surveys
We present a weak gravitational lensing analysis of 815 square degree of
-band imaging from the Kilo-Degree Survey (KiDS--800). In contrast to the
deep -band observations, which take priority during excellent seeing
conditions and form the primary KiDS dataset (KiDS--450), the complementary
yet shallower KiDS--800 spans a wide range of observing conditions. The
overlapping KiDS--800 and KiDS--450 imaging therefore provides a unique
opportunity to assess the robustness of weak lensing measurements. In our
analysis, we introduce two new `null' tests. The `nulled' two-point shear
correlation function uses a matched catalogue to show that the calibrated
KiDS--800 and KiDS--450 shear measurements agree at the level of \%. We use five galaxy lens samples to determine a `nulled' galaxy-galaxy
lensing signal from the full KiDS--800 and KiDS--450 surveys and find
that the measurements agree to \% when the KiDS--800 source
redshift distribution is calibrated using either spectroscopic redshifts, or
the 30-band photometric redshifts from the COSMOS survey.Comment: 24 pages, 20 figures. Submitted to MNRAS. Comments welcom
Testing KiDS cross-correlation redshifts with simulations
Measuring cosmic shear in wide-field imaging surveys requires accurate knowledge of the redshift distribution of all sources. The clustering-redshift technique exploits the angular cross-correlation of a target galaxy sample with unknown redshifts and a reference sample with known redshifts. It represents an attractive alternative to colour-based methods of redshift calibration. Here we test the performance of such clustering redshift measurements using mock catalogues that resemble the Kilo-Degree Survey (KiDS). These mocks are created from the MICE simulation and closely mimic the properties of the KiDS source sample and the overlapping spectroscopic reference samples. We quantify the performance of the clustering redshifts by comparing the cross-correlation results with the true redshift distributions in each of the five KiDS photometric redshift bins. Such a comparison to an informative model is necessary due to the incompleteness of the reference samples at high redshifts. Clustering mean redshifts are unbiased at |Îz|< 0.006 under these conditions. The redshift evolution of the galaxy bias of the reference and target samples represents one of the most important systematic errors when estimating clustering redshifts. It can be reliably mitigated at this level of precision using auto-correlation measurements and self-consistency relations, and will not become a dominant source of systematic error until the arrival of Stage-IV cosmic shear surveys. Using redshift distributions from a direct colour-based estimate instead of the true redshift distributions as a model for comparison with the clustering redshifts increases the biases in the mean to up to |Îz|âź0.04. This indicates that the interpretation of clustering redshifts in real-world applications will require more sophisticated (parameterised) models of the redshift distribution in the future. If such better models are available, the clustering-redshift technique promises to be a highly complementary alternative to other methods of redshift calibration
Testing KiDS cross-correlation redshifts with simulations
Measuring cosmic shear in wide-field imaging surveys requires accurate
knowledge of the redshift distribution of all sources. The clustering-redshift
technique exploits the angular cross-correlation of a target galaxy sample with
unknown redshifts and a reference sample with known redshifts, and is an
attractive alternative to colour-based methods of redshift calibration. We test
the performance of such clustering redshift measurements using mock catalogues
that resemble the Kilo-Degree Survey (KiDS). These mocks are created from the
MICE simulation and closely mimic the properties of the KiDS source sample and
the overlapping spectroscopic reference samples. We quantify the performance of
the clustering redshifts by comparing the cross-correlation results with the
true redshift distributions in each of the five KiDS photometric redshift bins.
Such a comparison to an informative model is necessary due to the
incompleteness of the reference samples at high redshifts. Clustering mean
redshifts are unbiased at under these conditions. The
redshift evolution of the galaxy bias can be reliably mitigated at this level
of precision using auto-correlation measurements and self-consistency
relations, and will not become a dominant source of systematic error until the
arrival of Stage-IV cosmic shear surveys. Using redshift distributions from a
direct colour-based estimate instead of the true redshift distributions as a
model for comparison with the clustering redshifts increases the biases in the
mean to up to . This indicates that the interpretation of
clustering redshifts in real-world applications will require more sophisticated
(parameterised) models of the redshift distribution in the future. If such
better models are available, the clustering-redshift technique promises to be a
highly complementary alternative to other methods of redshift calibration.Comment: 21 pages, 18 figures, 10 tables, submitted to A&
3D Cosmic Shear: Cosmology from CFHTLenS
This paper presents the first application of 3D cosmic shear to a wide-field
weak lensing survey. 3D cosmic shear is a technique that analyses weak lensing
in three dimensions using a spherical harmonic approach, and does not bin data
in the redshift direction. This is applied to CFHTLenS, a 154 square degree
imaging survey with a median redshift of 0.7 and an effective number density of
11 galaxies per square arcminute usable for weak lensing. To account for survey
masks we apply a 3D pseudo-Cl approach on weak lensing data, and to avoid
uncertainties in the highly non-linear regime, we separately analyse radial
wave numbers k<=1.5h/Mpc and k<=5.0h/Mpc, and angular wavenumbers l~400-5000.
We show how one can recover 2D and tomographic power spectra from the full 3D
cosmic shear power spectra and present a measurement of the 2D cosmic shear
power spectrum, and measurements of a set of 2-bin and 6-bin cosmic shear
tomographic power spectra; in doing so we find that using the 3D power in the
calculation of such 2D and tomographic power spectra from data naturally
accounts for a minimum scale in the matter power spectrum. We use 3D cosmic
shear to constrain cosmologies with parameters OmegaM, OmegaB, sigma8, h, ns,
w0, wa. For a non-evolving dark energy equation of state, and assuming a flat
cosmology, lensing combined with WMAP7 results in h=0.78+/-0.12,
OmegaM=0.252+/-0.079, sigma8=0.88+/-0.23 and w=-1.16+/-0.38 using only scales
k<=1.5h/Mpc. We also present results of lensing combined with first year Planck
results, where we find no tension with the results from this analysis, but we
also find no significant improvement over the Planck results alone. We find
evidence of a suppression of power compared to LCDM on small scales 1.5 < k <
5.0 h/Mpc in the lensing data, which is consistent with predictions of the
effect of baryonic feedback on the matter power spectrum.Comment: Full journal article here
http://mnras.oxfordjournals.org/content/442/2/1326.full.pdf+htm
Chandra Observations of the QSO Pair Q2345+007: Binary Quasar or Massive Dark Lens?
The components of the wide (7.3") separation quasar pair Q2345+007A,B
(z=2.15) have the most strikingly similar optical spectra seen to date (Steidel
& Sargent 1991) yet no detected lensing mass, making this system the best
candidate known for a massive (1e14 Msun) dark matter lens system. Here we
present results from a 65ksec Chandra observation designed to investigate
whether it is a binary quasar or a gravitational lens. We find no X-ray
evidence for a lensing cluster to a (0.5-2keV) flux limit of 2e-15 cgs, which
is consistent with lensing only for a reduced baryon fraction. Using the
Chandra X-ray observations of the quasars themselves, together with new and
published optical measurements, we use the observed emission properties of the
quasars for further tests between the lens and binary hypotheses. Assuming
similar line-of-sight absorption to the images, we find that their X-ray
continuum slopes are inconsistent (Gamma_A=2.30 and Gamma_B=0.83) as are their
X-ray to optical flux ratios. The probability that B suffers absorption
sufficient to account for these spectral differences is negligible. We present
new optical evidence that the flux ratio of the pair is variable, so the
time-delay in a lens scenario could cause some of the discrepancies. However,
adequately large variations in overall spectral energy distribution are rare in
individual QSOs. All new evidence here weighs strongly toward the binary
interpretation. Q2345+007 thus may represent the highest redshift example known
of interaction-triggered but as-yet unmerged luminous AGN.Comment: 15 pages, Latex, emulateapj style, including 3 tables and 5 figures.
Accepted Feb 1, 2002 for publication in ApJ Main Journal. See also
http://hea-www.harvard.edu/~pgreen/Papers.htm
The Shear TEsting Programme 1: Weak lensing analysis of simulated ground-based observations
The Shear TEsting Programme, STEP, is a collaborative project to improve the accuracy and reliability of all weak lensing measurements in preparation for the next generation of wide-field surveys. In this first STEP paper we present the results of a blind analysis of simulated ground-based observations of relatively simple galaxy morphologies. The most successful methods are shown to achieve percent level accuracy. From the cosmic shear pipelines that have been used to constrain cosmology, we find weak lensing shear measured to an accuracy that is within the statistical errors of current weak lensing analyses, with shear measurements accurate to better than 7%. The dominant source of measurement error is shown to arise from calibration uncertainties where the measured shear is over or under-estimated by a constant multiplicative factor. This is of concern as calibration errors cannot be detected through standard diagnostic tests. The measured calibration errors appear to result from stellar contamination, false object detection, the shear measurement method itself, selection bias and/or the use of biased weights. Additive systematics (false detections of shear) resulting from residual point-spread function anisotropy are, in most cases, reduced to below an equivalent shear of 0.001, an order of magnitude below cosmic shear distortions on the scales probed by current surveys. Our results provide a snapshot view of the accuracy of current ground-based weak lensing methods and a benchmark upon which we can improve. To this end we provide descriptions of each method tested and include details of the eight different implementations of the commonly used Kaiser, Squires and Broadhurst (1995) method (KSB+) to aid the improvement of future KSB+ analyses
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