B-modes in cosmic shear from source redshift clustering

By P. Schneider, L. V. Waerbeke, Y. Mellier. 2001

182 citations recorded by the source corpus.

Weak gravitational lensing by the large scale structure can be used to probe the dark matter distribution in the Universe directly and thus to probe cosmological models. The recent detection of cosmic shear by several groups has demonstrated the feasibility of this new mode of observational cosmology. In the currently most extensive analysis of cosmic shear, it was found that the shear eld contains unexpected modes, so-called B-modes, which are thought to be unaccountable for by lensing. B-modes can in principle be generated by an intrinsic alignment of galaxies from which the shear is measured, or may signify some remaining systematics in the data reduction and analysis. In this paper we show that B-modes in fact are produced by lensing itself. The eect comes about through the clustering of source galaxies, which in particular implies an angular separation-dependent clustering in redshift. After presenting the theory of the decomposition of a general shear eld into E- and B-modes, we calculate their respective power spectra and correlation functions for a clustered source distribution. Numerical and analytical estimates of the relative strength of these two modes show that the resulting B-mode is very small on angular scales larger than a few arcminutes, but its relative contribution rises quickly towards smaller angular scales, with comparable power in both modes at a few arcseconds. The relevance of this eect with regard to the current cosmic shear surveys is discussed; it can not account for the apparent detection of a B-mode contribution on large angular scales in the cosmic shear analysis of van Waerbeke et al. (2002).

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c7fe840202eacffd6bedd9d1ad1ada02617184f3

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Citations in the corpus

The Intrinsic Alignment of Galaxies and its Impact on Weak Gravitational Lensing in an Era of Precision Cosmology (2014, background): “The true lensing signal is necessarily curl-free, since the shear is related to the gradient of the potential γij(x) = (∂i∂j − 1 2 δij∇2)ψ(x), (173) except on small scales where source redshift clustering has an impact (Schneider et al., 2002).”
Very weak lensing in the CFHTLS Wide: Cosmology from cosmic shear in the linear regime (2007, methodology): “The covariance matrices for the shear two-point correlation functions are calculated using the expressions of Schneider et al. (2002a), valid for a Gaussian shear field.”
Dark energy constraints from cosmic shear power spectra: impact of intrinsic alignments on photometric redshift requirements (2007, background): “Cosmic shear produces only E-mode (curl-free) distortions, except on sub-arcminute scales where source clustering induces a B-mode signal (Schneider et al. 2002).”
Evidence of the accelerated expansion of the Universe from weak lensing tomography with COSMOS (2009, unknown): “…scales is weaker, is provided by the dispersion of the aperture mass (Schneider 1996) 〈M2ap/⊥〉(θ) = 1 2 ∫ 2θ 0 dϑϑ θ2 [ ξ+(ϑ)T+ ( ϑ θ ) ± ξ−(ϑ)T− ( ϑ θ )] , (10) with T± given in Schneider et al. (2002), where we employ the aperture mass weight function proposed by Schneider et al. (1998).”
Detection of large-scale intrinsic ellipticity—density correlation from the Sloan Digital Sky Survey and implications for weak lensing surveys (2005, background): “(7) There are lensing-induced contributions to the B-mode shear from other effects, such as multiple deflections (Cooray & Hu 2002; Hirata & Seljak 2003b; Cooray et al. 2005) and, on small scales, modulation of the effective source redshift by galaxy clustering (Schneider et al. 2002).”
First Cosmic Shear Results from the Canada-France-Hawaii Telescope Wide Synoptic Legacy Survey (2005, methodology): “Expressions for T (x) can be found in Crittenden et al. (2002) and Schneider et al. (2002b).”
Systematic errors in future weak-lensing surveys: requirements and prospects for self-calibration (2005, background): “It has been pointed out that second-order corrections in the shear predictions can be important (Schneider et al. 2002, Hamana et al. 2002, Cooray & Hu 2002, White 2005, Dodelson & Zhang 2005, Dodelson et al. 2005).”
Galaxy Alignments: Observations and Impact on Cosmology (2015, background): “…j|), where δi j is the Kronecker delta, σ denotes the total intrinsic ellipticity dispersion, and the angle brackets indicate an ensemble average over the intrinsic ellipticity distribution and over the cosmic shear field, assuming randomly-oriented intrinsic ellipticities (Schneider et al. 2002a).”
KiDS+VIKING-450: Cosmic shear tomography with optical and infrared data (2018, background): “…be produced from higher-order terms beyond the first-order Born approximation (Schneider et al. 1998; Hilbert et al. 2009), source clustering of galaxies and intrinsic alignments (Schneider et al. 2002), as well as cosmic strings and some alternatives to ΛCDM (see for example Thomas et al. 2017).”
Ray-tracing through the Millennium Simulation: Born corrections and lens-lens coupling in cosmic shear and galaxy-galaxy lensing (2008, methodology): “These artifacts can be avoided by using aperture masses to quantify the shear E- and B-mode contributions (Crittenden et al. 2002; Schneider et al. 2002).”
CFHTLenS: combined probe cosmological model comparison using 2D weak gravitational lensing (2012, background): “The filter functions for the aperture-mass dispersion, defined in Schneider et al. (2002a), are for x < 2 T+(x) = 6(2 − 15x 2) 5 [ 1 − 2 π arcsin(x/2) ] + x √ 4 − x2 100π × (120 + 2320x2 − 754x4 + 132x6 − 9x8) ; T−(x) = 192 35π x3 ( 1 − x 2 4 )7/2 .”
The DES Science Verification weak lensing shear catalogues (2015, background): “The corresponding divergence-free “B-mode” field can be considered as corresponding to an imaginary convergence (Schneider et al. 2002).”
COSMOS: Three-dimensional Weak Lensing and the Growth of Structure (2007, background): “The two-point shear correlation functions can be expressed (Schneider et al. 2002) in terms of the projected power spectrum as C1( ) ¼ 1 4 Z 1 0 C ‘ J0(‘ )þ J4(‘ ) ‘ d‘; ð7Þ C2( ) ¼ 1 4 Z 1 0 C ‘ J0(‘ ) J4(‘ ) ‘ d‘: ð8Þ These can be measured by averaging over galaxy pairs, as C1(a) ¼ r1(r) r 1(rþ…”
The Shear Testing Programme – I. Weak lensing analysis of simulated ground-based observations (2005, background): “Implementing diagnostic statistics that decompose cosmic shear signals into their lensing E-modes and non-lensing B-modes (Crittenden et al. 2002; Schneider et al. 2002; Brown et al. 2003) immediately alerts us to the presence of systematic error within our data set.”
The skewness of the aperture mass statistic (2003, methodology): “The measurements shown are spaced by approximately a factor of 2 in R, because this is where the measurements become independent of each other (Schneider et al. 2002).”