Publications


CFHTLenS: Combined probe cosmological model comparison using 2D weak gravitational lensing

Monthly Notices of the Royal Astronomical Society 430 (2013) 2200-2220

M Kilbinger, L Fu, C Heymans, F Simpson, J Benjamin, T Erben, J Harnois-Déraps, H Hoekstra, H Hildebrandt, TD Kitching, Y Mellier, L Miller, L Van Waerbeke, K Benabed, C Bonnett, J Coupon, MJ Hudson, K Kuijken, B Rowe, T Schrabback, E Semboloni, S Vafaei, M Velander

We present cosmological constraints from 2D weak gravitational lensing by the large-scale structure in the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) which spans 154 deg2 in five optical bands. Using accurate photometric redshifts and measured shapes for 4.2 million galaxies between redshifts of 0.2 and 1.3, we compute the 2D cosmic shear correlation function over angular scales ranging between 0.8 and 350 arcmin. Using nonlinear models of the dark-matter power spectrum, we constrain cosmological parameters by exploring the parameter space with Population Monte Carlo sampling. The best constraints from lensing alone are obtained for the small-scale density-fluctuations amplitude σ8 scaled with the total matter density Ωm. For a flat Λcold dark matter (ΛCDM) model we obtain Σ8(Ωm/0.27)0.6 = 0.79 ± 0.03. We combine the CFHTLenS data with 7-year Wilkinson Microwave Anisotropy Probe (WMAP7), baryonic acoustic oscillations (BAO): SDSS-III (BOSS) and a Hubble Space Telescope distance-ladder prior on the Hubble constant to get joint constraints. For a flat ΛCDM model, we find Ωm = 0.283 ± 0.010 and Σ8 = 0.813 ± 0.014. In the case of a curved wCDM universe, we obtain Ωm = 0.27 ± 0.03, Σ8 = 0.83 ± 0.04, w0 = -1.10 ± 0.15 and Ωk = 0.006+0.006-0.004. We calculate the Bayesian evidence to compare flat and curved ΛCDM and dark-energy CDM models. From the combination of all four probes, we find models with curvature to be at moderately disfavoured with respect to the flat case. A simple dark-energy model is indistinguishable from ΛCDM. Our results therefore do not necessitate any deviations from the standard cosmological model. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


CFHTLenS: Testing the laws of gravity with tomographic weak lensing and redshift-space distortions

Monthly Notices of the Royal Astronomical Society 429 (2013) 2249-2263

F Simpson, C Heymans, D Parkinson, C Blake, M Kilbinger, J Benjamin, T Erben, H Hildebrandt, H Hoekstra, TD Kitching, Y Mellier, L Miller, L Van Waerbeke, J Coupon, L Fu, J Harnois-Déraps, MJ Hudson, K Kuijken, B Rowe, T Schrabback, E Semboloni, S Vafaei, M Velander

Dark energy may be the first sign of new fundamental physics in the Universe, taking either a physical form or revealing a correction to Einsteinian gravity. Weak gravitational lensing and galaxy peculiar velocities provide complementary probes of general relativity, and in combination allow us to test modified theories of gravity in a unique way.We perform such an analysis by combining measurements of cosmic shear tomography from the Canada-France- Hawaii Telescope Lensing Survey (CFHTLenS) with the growth of structure from theWiggleZ Dark Energy Survey and the Six-degree-Field Galaxy Survey, producing the strongest existing joint constraints on the metric potentials that describe general theories of gravity. For scaleindependent modifications to the metric potentials which evolve linearly with the effective dark energy density, we find present-day cosmological deviations in the Newtonian potential and curvature potential from the prediction of general relativity to be δψ/ψ = 0.05 ± 0.25 and δφ/φ=-0.05 ± 0.3, respectively (68 per cent confidence limits). © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


CFHTLenS tomographic weak lensing cosmological parameter constraints: Mitigating the impact of intrinsic galaxy alignments

Monthly Notices of the Royal Astronomical Society 432 (2013) 2433-2453

C Heymans, E Grocutt, A Heavens, M Kilbinger, TD Kitching, F Simpson, J Benjamin, T Erben, H Hildebrandt, H Hoekstra, Y Mellier, L Miller, L Van Waerbeke, ML Brown, J Coupon, L Fu, J Harnois-Déraps, MJ Hudson, K Kuijken, B Rowe, T Schrabback, E Semboloni, S Vafaei, M Velander

We present a finely binned tomographic weak lensing analysis of the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) mitigating contamination to the signal from the presence of intrinsic galaxy alignments via the simultaneous fit of a cosmological model and an intrinsic alignment model. CFHTLenS spans 154 square degrees in five optical bands, with accurate shear and photometric redshifts for a galaxy sample with a median redshift of zm = 0.70. We estimate the 21 sets of cosmic shear correlation functions associated with six redshift bins, each spanning the angular range of 1.5 < θ < 35 arcmin. We combine this CFHTLenS data with auxiliary cosmological probes: the cosmic microwave background with data from WMAP7, baryon acoustic oscillations with data from Baryon Oscillation Spectroscopic Survey and a prior on the Hubble constant from the Hubble Space Telescope distance ladder. This leads to constraints on the normalization of the matter power spectrum σ8 = 0.799 ± 0.015 and the matter density parameter ωm = 0.271 ± 0.010 for a flat Λ cold dark matter (ΛCDM) cosmology. For a flat wCDM cosmology, we constrain the dark energy equation-of-state parameter w = -1.02 ± 0.09. We also provide constraints for curved ΛCDM and wCDM cosmologies.We find the intrinsic alignment contamination to be galaxy-type dependent with a significant intrinsic alignment signal found for early-type galaxies, in contrast to the late-type galaxy sample for which the intrinsic alignment signal is found to be consistent with zero. © 2013 The Author. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Size magnification as a complement to cosmic shear

Monthly Notices of the Royal Astronomical Society 430 (2013) 2844-2853

B Casaponsa, AF Heavens, TD Kitching, L Miller, RB Barreiro, E Martínez-González

We investigate the extent to which cosmic size magnification may be used to complement cosmic shear in weak gravitational lensing surveys, with a view to obtaining high-precision estimates of cosmological parameters. Using simulated galaxy images, we find that unbiased estimation of the convergence field is possible using galaxies with angular sizes larger than the point spread function (PSF) and signal-to-noise ratio in excess of 10. The statistical power is similar to, but not quite as good as, cosmic shear, and it is subject to different systematic effects. Application to ground-based data will be challenging, with relatively large empirical corrections required to account for the fact that many galaxiesare smaller than the PSF, but for space-based data with 0.1-0.2 arcsec resolution, the size distribution of galaxies brighter than i≃24 is almost ideal for accurate estimation of cosmic size magnification. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


CFHTLenS: Higher order galaxy-mass correlations probed by galaxy-galaxy-galaxy lensing

Monthly Notices of the Royal Astronomical Society 430 (2013) 2476-2498

P Simon, T Erben, P Schneider, C Heymans, H Hildebrandt, H Hoekstra, TD Kitching, Y Mellier, L Miller, L Van Waerbeke, C Bonnett, J Coupon, L Fu, MJ Hudson, K Kuijken, BTP Rowe, T Schrabback, E Semboloni, M Velander

We present the first direct measurement of the galaxy-matter bispectrum as a function of galaxy luminosity, stellar mass and type of spectral energy distribution (SED). Our analysis uses a galaxy-galaxy-galaxy lensing technique (G3L), on angular scales between 9 arcsec and 50 arcmin, to quantify (i) the excess surface mass density around galaxy pairs (excess mass hereafter) and (ii) the excess shear-shear correlations around single galaxies, both of which yield a measure of two types of galaxy-matter bispectra. We apply our method to the state-of-the-art Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), spanning 154 square degrees. This survey allows us to detect a significant change of the bispectra with lens properties. Measurements for lens populations with distinct redshift distributions become comparable by a newly devised normalization technique. That will also aid future comparisons to other surveys or simulations. A significant dependence of the normalized G3L statistics on luminosity within-23=Mr=-18 and stellarmass within 5×109M⊙ =M* <2×1011M⊙ is found (h = 0.73). Both bispectra exhibit a stronger signal for more luminous lenses or those with higher stellar mass (up to a factor of 2-3). This is accompanied by a steeper equilateral bispectrum for more luminous or higher stellar mass lenses for the excess mass. Importantly, we find the excess mass to be very sensitive to galaxy type as recently predicted with semianalytic galaxy models: luminous (Mr < -21) late-type galaxies show no detectable signal, while all excess mass detected for luminous galaxies seems to be associated with early-type galaxies. We also present the first observational constraints on third-order stochastic galaxy biasing parameters. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


CFHTLenS tomographic weak lensing: Quantifying accurate redshift distributions

Monthly Notices of the Royal Astronomical Society 431 (2013) 1547-1564

J Benjamin, L Van waerbeke, C Heymans, M Kilbinger, T Erben, H Hildebrandt, H Hoekstra, TD Kitching, Y Mellier, L Miller, B Rowe, T Schrabback, F Simpson, J Coupon, L Fu, J Harnois-déraps, MJ Hudson, K Kuijken, E Semboloni, S Vafaei, M Velander

The Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) comprises deep multicolour (u*g'r'i'z') photometry spanning 154 deg2, with accurate photometric redshifts and shape measurements. We demonstrate that the redshift probability distribution function summed over galaxies provides an accurate representation of the galaxy redshift distribution accounting for random and catastrophic errors for galaxies with best-fitting photometric redshifts zp < 1.3.We present cosmological constraints using tomographic weak gravitational lensing by large-scale structure. We use two broad redshift bins 0.5 < zp ≤ 0.85 and 0.85 < zp ≤ 1.3 free of intrinsic alignment contamination, and measure the shear correlation function on angular scales in the range ∼1-40 arcmin. We show that the problematic redshift scaling of the shear signal, found in previous Canada-France-Hawaii Telescope Legacy Survey data analyses, does not affect the CFHTLenS data. For a flat Λ cold dark matter model and a fixed matter density Ωm = 0.27, we find the normalization of the matter power spectrum σ8 = 0.771 ± 0.041. When combined with cosmic microwave background data (Wilkinson Microwave Anisotropy Probe 7-year results), baryon acoustic oscillation data (BOSS) and a prior on the Hubble constant from the Hubble Space Telescope distance ladder, we find that CFHTLenS improves the precision of the fully marginalized parameter estimates by an average factor of 1.5-2. Combining our results with the above cosmological probes, we find Ωm = 0.2762 ± 0.0074 and σ8 = 0.802 ± 0.013. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


CFHTlens: The environmental dependence of galaxy halo masses from weak lensing

Monthly Notices of the Royal Astronomical Society 431 (2013) 1439-1452

BR Gillis, MJ Hudson, T Erben, C Heymans, H Hildebrandt, H Hoekstra, TD Kitching, Y Mellier, L Miller, L van Waerbeke, C Bonnett, J Coupon, L Fu, S Hilbert, BTP Rowe, T Schrabback, E Semboloni, E van Uitert, M Velander

We use weak gravitational lensing to analyse the dark matter haloes around satellite galaxies in galaxy groups in the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) data set. This data set is derived from the Canada-France-Hawaii Telescope Legacy Survey Wide survey, and encompasses 154 deg2 of high-quality shape data. Using the photometric redshifts, we divide the sample of lens galaxies with stellar masses in the range 109-1010.5M⊙ into those likely to lie in high-density environments (HDE) and those likely to lie in low-density environments (LDE). Through comparison with galaxy catalogues extracted from the Millennium Simulation, we show that the sample of HDE galaxies should primarily (~61 per cent) consist of satellite galaxies in groups, while the sample of LDE galaxies should consist of mostly (~87 per cent) non-satellite (field and central) galaxies. Comparing the lensing signals around samples of HDE and LDE galaxies matched in stellar mass, the lensing signal around HDE galaxies clearly shows a positive contribution from their host groups on their lensing signals at radii of ~500-1000 kpc, the typical separation between satellites and group centres. More importantly, the subhaloes of HDE galaxies are less massive than those around LDE galaxies by a factor of 0.65 ± 0.12, significant at the 2.9σ level. A natural explanation is that the haloes of satellite galaxies are stripped through tidal effects in the group environment. Our results are consistent with a typical tidal truncation radius of ~40 kpc. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Bayesian galaxy shape measurement for weak lensing surveys - III. Application to the Canada-France-Hawaii Telescope Lensing Survey

Monthly Notices of the Royal Astronomical Society 429 (2013) 2858-2880

L Miller, C Heymans, TD Kitching, L van Waerbeke, T Erben, H Hildebrandt, H Hoekstra, Y Mellier, BTP Rowe, J Coupon, JP Dietrich, L Fu, J Harnois-D́eraps, MJ Hudson, M Kilbinger, K Kuijken, T Schrabback, E Semboloni, S Vafaei, M Velander

A likelihood-based method for measuring weak gravitational lensing shear in deep galaxy surveys is described and applied to the Canada-France-Hawaii Telescope (CFHT) Lensing Survey (CFHTLenS). CFHTLenS comprises 154 deg2 of multi-colour optical data from the CFHT Legacy Survey, with lensing measurements being made in the i' band to a depth i' AB < 24.7, for galaxies with signal-to-noise ratio νSN ( 10. The method is based on the lensfit algorithm described in earlier papers, but here we describe a full analysis pipeline that takes into account the properties of real surveys. The method creates pixel-based models of the varying point spread function (PSF) in individual image exposures. It fits PSF-convolved two-component (disc plus bulge) models to measure the ellipticity of each galaxy, with Bayesian marginalization over model nuisance parameters of galaxy position, size, brightness and bulge fraction. The method allows optimal joint measurement of multiple, dithered image exposures, taking into account imaging distortion and the alignment of the multiple measurements. We discuss the effects of noise bias on the likelihood distribution of galaxy ellipticity. Two sets of image simulations that mirror the observed properties of CFHTLenS have been created to establish the method's accuracy and to derive an empirical correction for the effects of noise bias. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.


Defining a weak lensing experiment in space

Monthly Notices of the Royal Astronomical Society 431 (2013) 3103-3126

M Cropper, H Hoekstra, T Kitching, R Massey, J Amiaux, L Miller, Y Mellier, J Rhodes, B Rowe, S Pires, C Saxton, R Scaramella

This paper describes the definition of a typical next-generation space-based weak gravitational lensing experiment. We first adopt a set of top-level science requirements from the literature, based on the scale and depth of the galaxy sample, and the avoidance of systematic effects in the measurements which would bias the derived shear values. We then identify and categorize the contributing factors to the systematic effects, combining them with the correct weighting, in such a way as to fit within the top-level requirements. We present techniques which permit the performance to be evaluated and explore the limits at which the contributing factors can be managed. Besides the modelling biases resulting from the use of weighted moments, the main contributing factors are the reconstruction of the instrument point spread function, which is derived from the stellar images on the image, and the correction of the charge transfer inefficiency in the CCD detectors caused by radiation damage. © 2013 The Authors.


CFHTLenS: The Canada-France-Hawaii telescope lensing survey - Imaging data and catalogue products

Monthly Notices of the Royal Astronomical Society 433 (2013) 2545-2563

T Erben, H Hildebrandt, L Miller, L Van Waerbeke, C Heymans, H Hoekstra, TD Kitching, Y Mellier, J Benjamin, C Blake, C Bonnett, O Cordes, J Coupon, L Fu, R Gavazzi, B Gillis, E Grocutt, SDJ Gwyn, K Holhjem, MJ Hudson, M Kilbinger, K Kuijken, M Milkeraitis, BTP Rowe, T Schrabback, E Semboloni, P Simon, M Smit, O Trader, S Vafaei, E Van Uitert, M Velander

We present data products from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS). CFHTLenS is based on the Wide component of the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). It encompasses 154 deg2 of deep, optical, high-quality, sub-arcsecond imaging data in the five optical filters u′g′r′i′z′. The scientific aims of the CFHTLenS team are weak gravitational lensing studies supported by photometric redshift estimates for the galaxies. This paper presents our data processing of the complete CFHTLenS data set. We were able to obtain a data set with very good image quality and high-quality astrometric and photometric calibration. Our external astrometric accuracy is between 60 and 70 mas with respect to Sloan Digital Sky Survey (SDSS) data, and the internal alignment in all filters is around 30 mas. Our average photometric calibration shows a dispersion of the order of 0.01-0.03 mag for g′r′i′ z′ and about 0.04 mag for u* with respect to SDSS sources down to iSDSS ≤ 21. We demonstrate in accompanying papers that our data meet necessary requirements to fully exploit the survey for weak gravitational lensing analyses in connection with photometric redshift studies. In the spirit of the CFHTLS, all our data products are released to the astronomical community via the Canadian Astronomy Data Centre at http://www.cadc-ccda.hia-iha.nrc-cnrc. gc.ca/community/CFHTLens/query.html. We give a description and how-to manuals of the public products which include image pixel data, source catalogues with photometric redshift estimates and all relevant quantities to perform weak lensing studies.© 2013 The Authors.


Origins of weak lensing systematics, and requirements on future instrumentation (or knowledge of instrumentation)

Monthly Notices of the Royal Astronomical Society 429 (2013) 661-678

R Massey, H Hoekstra, T Kitching, J Rhodes, M Cropper, J Amiaux, D Harvey, Y Mellier, M Meneghetti, L Miller, S Paulin-Henriksson, S Pires, R Scaramella, T Schrabback

The first half of this paper explores the origin of systematic biases in the measurement of weak gravitational lensing. Compared to previous work, we expand the investigation of point spread function instability and fold in for the first time the effects of non-idealities in electronic imaging detectors and imperfect galaxy shape measurement algorithms. Together, these now explain the additive A(l) and multiplicative M(l) systematics typically reported in current lensing measurements. We find that overall performance is driven by a product of a telescope/camera's absolute performance, and our knowledge about its performance. The second half of this paper propagates any residual shear measurement biases through to their effect on cosmological parameter constraints. Fully exploiting the statistical power of Stage IV weak lensing surveys will require additive biasesA 1.8 × 10-12 and multiplicative biases M 4.0 × -3. These can be allocated between individual budgets in hardware, calibration data and software, using results from the first half of the paper. If instrumentation is stable and well calibrated, we find extant shear measurement software from Gravitational Lensing Accuracy Testing 2010 (GREAT10) already meet requirements on galaxies detected at signal-to-noise ratio = 40. Averaging over a population of galaxies with a realistic distribution of sizes, it also meets requirements for a 2D cosmic shear analysis from space. If used on fainter galaxies or for 3D cosmic shear tomography, existing algorithms would need calibration on simulations to avoid introducing bias at a level similar to the statistical error. Requirements on hardware and calibration data are discussed in more detail in a companion paper. Our analysis is intentionally general, but is specifically being used to drive the hardware and ground segment performance budget for the design of the European Space Agency's recently selected Euclid mission. ©2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.


The contribution of TP-AGB stars to the mid-infrared colors of Nearby Galaxies

Astrophysical Journal 753 (2012)

NE Chisari, DD Kelson

We study the mid-infrared color space of 30 galaxies from the Spitzer Infrared Nearby Galaxies Survey (SINGS) survey for which Sloan Digital Sky Survey data are also available. We construct two-color maps for each galaxy and compare them to results obtained from combining Maraston evolutionary synthesis models, galactic thermally pulsating asymptotic giant branch (TP-AGB) colors, and smooth star formation histories. For most of the SINGS sample, the spatially extended mid-IR emission seen by Spitzer in normal galaxies is consistent with our simple model in which circumstellar dust from TP-AGB stars dominates at 8 and 24 μm. There is a handful of exceptions that we identify as galaxies that have high star formation rates presumably with star formation histories that cannot be assumed to be smooth, or anemic galaxies, which were depleted of their H I at some point during their evolution and have very low ongoing star formation rates. © 2012. The American Astronomical Society. All rights reserved..


The impact of high spatial frequency atmospheric distortions on weak-lensing measurements

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY 421 (2012) 381-389

C Heymans, B Rowe, H Hoekstra, L Miller, T Erben, T Kitching, L Van Waerbeke


CFHTLenS: Improving the quality of photometric redshifts with precision photometry

Monthly Notices of the Royal Astronomical Society 421 (2012) 2355-2367

H Hildebrandt, T Erben, K Kuijken, L van Waerbeke, C Heymans, J Coupon, J Benjamin, C Bonnett, L Fu, H Hoekstra, TD Kitching, Y Mellier, L Miller, M Velander, MJ Hudson, BTP Rowe, T Schrabback, E Semboloni, N Benítez

Here we present the results of various approaches to measure accurate colours and photometric redshifts (photo-z) from wide-field imaging data. We use data from the Canada-France-Hawaii Telescope Legacy Survey which have been re-processed by the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) team in order to carry out a number of weak gravitational lensing studies. An emphasis is put on the correction of systematic effects in the photo-z arising from the different point spread functions (PSFs) in the five optical bands. Different ways of correcting these effects are discussed and the resulting photo-z accuracies are quantified by comparing the photo-z to large spectroscopic redshift (spec-z) data sets. Careful homogenization of the PSF between bands leads to increased overall accuracy of photo-z. The gain is particularly pronounced at fainter magnitudes where galaxies are smaller and flux measurements are affected more by PSF effects. We discuss ways of defining more secure subsamples of galaxies as well as a shape- and colour-based star-galaxy separation method, and we present redshift distributions for different magnitude limits. We also study possible re-calibrations of the photometric zero-points (ZPs) with the help of galaxies with known spec-z. We find that if PSF effects are properly taken into account, a re-calibration of the ZPs becomes much less important suggesting that previous such re-calibrations described in the literature could in fact be mostly corrections for PSF effects rather than corrections for real inaccuracies in the ZPs. The implications of this finding for future surveys like the Kilo Degree Survey (KiDS), Dark Energy Survey (DES), Large Synoptic Survey Telescope or Euclid are mixed. On the one hand, ZP re-calibrations with spec-z values might not be as accurate as previously thought. On the other hand, careful PSF homogenization might provide a way out and yield accurate, homogeneous photometry without the need for full spectroscopic coverage. This is the first paper in a series describing the technical aspects of CFHTLenS. © 2012 The Authors Monthly Notices of the Royal Astronomical Society © 2012 RAS.


CFHTLenS: The Canada-France-Hawaii Telescope Lensing Survey

Monthly Notices of the Royal Astronomical Society 427 (2012) 146-166

C Heymans, L Van Waerbeke, L Miller, T Erben, H Hildebrandt, H Hoekstra, TD Kitching, Y Mellier, P Simon, C Bonnett, J Coupon, L Fu, J Harnois-Déraps, MJ Hudson, M Kilbinger, K Kuijken, B Rowe, T Schrabback, E Semboloni, E van Uitert, S Vafaei, M Velander

We present the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS) that accurately determines a weak gravitational lensing signal from the full 154 deg 2 of deep multicolour data obtained by the CFHT Legacy Survey. Weak gravitational lensing by large-scale structure is widely recognized as one of the most powerful but technically challenging probes of cosmology. We outline the CFHTLenS analysis pipeline, describing how and why every step of the chain from the raw pixel data to the lensing shear and photometric redshift measurement has been revised and improved compared to previous analyses of a subset of the same data. We present a novel method to identify data which contributes a non-negligible contamination to our sample and quantify the required level of calibration for the survey. Through a series of cosmology-insensitive tests we demonstrate the robustness of the resulting cosmic shear signal, presenting a science-ready shear and photometric redshift catalogue for future exploitation. © 2012 The Authors Monthly Notices of the Royal Astronomical Society. © 2012 RAS.


A filament of dark matter between two clusters of galaxies

Nature 487 (2012) 202-204

JP Dietrich, N Werner, D Clowe, A Finoguenov, T Kitching, L Miller, A Simionescu

It is a firm prediction of the concordance cold-dark-matter cosmological model that galaxy clusters occur at the intersection of large-scale structure filaments. The thread-like structure of this 'cosmic web' has been traced by galaxy redshift surveys for decades. More recently, the warm-hot intergalactic medium (a sparse plasma with temperatures of 10 5 kelvin to 10 7 kelvin) residing in low-redshift filaments has been observed in emission and absorption. However, a reliable direct detection of the underlying dark-matter skeleton, which should contain more than half of all matter, has remained elusive, because earlier candidates for such detections were either falsified or suffered from low signal-to-noise ratios and unphysical misalignments of dark and luminous matter. Here we report the detection of a dark-matter filament connecting the two main components of the Abell 222/223 supercluster system from its weak gravitational lensing signal, both in a non-parametric mass reconstruction and in parametric model fits. This filament is coincident with an overdensity of galaxies and diffuse, soft-X-ray emission, and contributes a mass comparable to that of an additional galaxy cluster to the total mass of the supercluster. By combining this result with X-ray observations, we can place an upper limit of 0.09 on the hot gas fraction (the mass of X-ray-emitting gas divided by the total mass) in the filament. © 2012 Macmillan Publishers Limited. All rights reserved.


Erratum: Connection between Newtonian simulations and general relativity (Physical Review D - Particles, Fields, Gravitation and Cosmology (2011) 84 (123505))

Physical Review D - Particles, Fields, Gravitation and Cosmology 84 (2011)

NE Chisari, M Zaldarriaga


Connection between Newtonian simulations and general relativity

Physical Review D - Particles, Fields, Gravitation and Cosmology 83 (2011)

NE Chisari, M Zaldarriaga

On large scales, comparable to the horizon, the observable clustering properties of galaxies are affected by various general relativistic effects. To calculate these effects one needs to consistently solve for the metric, densities, and velocities in a specific coordinate system or gauge. The method of choice for simulating large-scale structure is numerical N-body simulations which are performed in the Newtonian limit. Even though one might worry that the use of the Newtonian approximation would make it impossible to use these simulations to compute properties on very large scales, we show that the simulations are still solving the dynamics correctly even for long modes and we give formulas to obtain the position of particles in the conformal Newtonian gauge given the positions computed in the simulation. We also give formulas to convert from the output coordinates of N-body simulations to the observable coordinates of the particles. © 2011 American Physical Society.


Erratum: On the efficiency of production of the Fe Kα emission line in neutral matter

Monthly Notices of the Royal Astronomical Society 415 (2011) 3966-3967

T Yaqoob, KD Murphy, L Miller, TJ Turner


3D photometric cosmic shear

Monthly Notices of the Royal Astronomical Society 413 (2011) 2923-2934

TD Kitching, AF Heavens, L Miller

Here we present a number of improvements to weak lensing 3D power spectrum analysis, 3D cosmic shear, that uses the shape and redshift information of every galaxy to constrain cosmological parameters. We show how photometric redshift probability distributions for individual galaxies can be directly included in this statistic with no averaging. We also include the Limber approximation, considerably simplifying full 3D cosmic shear analysis, and we investigate its range of applicability. Finally we show the relationship between weak lensing tomography and the 3D cosmic shear field itself; the steps connecting them being the Limber approximation, a harmonic-space transform and a discretization in wavenumber. Each method has its advantages; 3D cosmic shear analysis allows straightforward inclusion of all relevant modes, thus ensuring minimum error bars, and direct control of the range of physical wavenumbers probed, to avoid the uncertain highly non-linear regime. On the other hand, tomography is more convenient for checking systematics through direct investigation of the redshift dependence of the signal. Finally, for tomography, we suggest that the angular modes probed should be redshift dependent, to recover some of the 3D advantages. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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