Intrinsic alignment-lensing interference as a contaminant of cosmic shear

By C. Hirata, Uros Seljak. 2004

393 citations recorded by the source corpus.

Cosmic shear surveys have great promise as tools for precision cosmology, but can be subject to systematic errors including intrinsic ellipticity correlations of the source galaxies. The intrinsic alignments are believed to be small for deep surveys, but this is based on intrinsic and lensing distortions being uncorrelated. Here we show that the gravitational lensing shear and intrinsic shear need not be independent: correlations between the tidal field and the intrinsic shear cause the intrinsic shear of nearby galaxies to be correlated with the gravitational shear acting on more distant galaxies. We estimate the magnitude of this effect for two simple intrinsic-alignment models: one in which the galaxy ellipticity is linearly related to the tidal field, and one in which it is quadratic in the tidal field as suggested by tidal torque theory. The first model predicts a gravitational-intrinsic (GI) correlation that can be much greater than the intrinsic-intrinsic (II) correlation for broad redshift distributions, and that remains when galaxies pairs at similar redshifts are rejected. The second model, in its simplest form, predicts no gravitational-intrinsic correlation. In the first model, and assuming a normalization consistent with recently claimed detections of intrinsic correlations, we find that the GI correlation term can exceed the usual II term by >1 order of magnitude and the intrinsic correlation induced B-mode by 2 orders of magnitude. These interference effects can suppress the lensing power spectrum for a single broad redshift bin by of order ∼10% at zs=1 and ∼30% at zs=0.5. We conclude that, depending on the intrinsic-alignment model, the GI correlation may be the dominant contaminant of the lensing signal and can even affect cross spectra between widely separated bins. We describe two ways to constrain this effect, one based on density-shear correlations and one based on scaling of the cross correlation tomography signal with redshift.

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Citations in the corpus

Cosmological constraints from the 100-deg2 weak-lensing survey (2007, background): “What is currently uncertain however is the level of systematic error that arises from shear–ellipticity correlations (Hirata & Seljak 2004; Mandelbaum et al. 2006; Heymans et al. 2006b; Hirata et al. 2007) which could reduce the amplitude of the measured shear correlation function by ∼10 per cent…”
CFHTLenS: combined probe cosmological model comparison using 2D weak gravitational lensing (2012, methodology): “Secondly, we can include low-redshift galaxies without having to consider intrinsic alignments (IA; Hirata & Seljak 2004).”
Detection of large-scale intrinsic ellipticity—density correlation from the Sloan Digital Sky Survey and implications for weak lensing surveys (2005, methodology): “Hirata & Seljak (2004) provided formulas relating the power spectra in Eqs.”
Gravitational lensing (2010, background): “The authors of [195] pointed out that foreground galaxies are aligned with the large-scale structures lensing background galaxies, thus giving rise to a higher-order alignment between galaxies at different redshifts.”
KiDS-450: cosmological parameter constraints from tomographic weak gravitational lensing (2016, methodology): “In contrast, the commonly used linear-alignment theory which we adopt to model the impact of intrinsic galaxy alignments (see Section 4.2) predicts B modes which contribute only to the sub-dominant ‘II’ term at roughly an order of magnitude lower than the ‘II’ E-mode signal (Hirata & Seljak 2004).”
Observational probes of cosmic acceleration (2012, background): “An alternative implementation of this idea is nulling (Hirata and Seljak, 2004; Joachimi and Schneider, 2008, 2009), constructing a synthetic redshift slice by weighting of the different zβ whose window function Weff,syn[DC(zα)] = ∑ β wβW [DC(zα),DC (zβ)] = 0.”
Intrinsic alignments of SDSS-III BOSS LOWZ sample galaxies (2014, background): “Hirata & Seljak (2004) developed the linear alignment model for the intrinsic alignments, assuming that intrinsic alignments are set by tidal fields at the time of galaxy formation (Catelan, Kamionkowski & Blandford 2001).”
Properties of dark matter haloes in clusters, filaments, sheets and voids (2006, background): “The presence of alignments between large-scale structures and halo spins could produce a coherent alignment of galaxy shapes and thus generate a systematic contamination in weak lensing maps of cosmic shear (e.g. Hirata & Seljak 2004; Heymans et al. 2006).”
Dancing in the dark: galactic properties trace spin swings along the cosmic web (2014, background): “…with the cosmic structure, much observational effort has been made to control the level of intrinsic alignments of galaxies as a potential source of systematic errors in weak gravitational lensing measurements (e.g. Croft & Metzler 2000; Heavens, Refregier & Heymans 2000; Hirata & Seljak 2004).”
KiDS+VIKING-450: Cosmic shear tomography with optical and infrared data (2018, unknown): “…intrinsic alignment model as in H17, which modifies the 2-point shear correlation functions by adding two more terms describing the II and GI effects (Hirata & Seljak 2004): ξ̂± = ξ± + ξ II ± + ξ GI ± , (8) where ξII± and ξ GI ± are calculated from the II and GI power spectra PII(k, z) =…”
Dark energy constraints from cosmic shear power spectra: impact of intrinsic alignments on photometric redshift requirements (2007, background): “As detailed in Hirata and Seljak (2004) the shear power spectra between redshift bins i and j come from the sum of three terms Cℓ(ij) = C GG ℓ(ij) + C II ℓ(ij) + C GI ℓ(ij) (2) where the first term is the usual gravitational lensing contribution, the second term arises from the intrinsic alignments…”
Cosmological constraints from cosmic shear two-point correlation functions with HSC survey first-year data (2019, methodology): “We employ the standard theoretical model for these terms, namely, the nonlinear modification of the tidal alignment model (Hirata & Seljak 2004; Bridle & King 2007; Joachimi et al. 2011).”
Simultaneous measurement of cosmology and intrinsic alignments using joint cosmic shear and galaxy number density correlations (2009, methodology): “…Lee & Pen 2000; Catelan et al. 2001; Crittenden et al. 2001; Jing 2002; Mackey et al. 2002; Hirata & Seljak 2004; Bridle & Abdalla 2007; Schneider & Bridle 2010), as well as the alignment of the spin or the shape of a galaxy with its own…”
KiDS-450 + 2dFLenS: Cosmological parameter constraints from weak gravitational lensing tomography and overlapping redshift-space galaxy clustering (2017, methodology): “This standard parametrization of the intrinsic alignments does not include a scale dependence and assumes the validity of the ‘non-linear linear alignment’ model over the scales probed by our measurements (Hirata & Seljak 2004; Bridle & King 2007; also see Singh, Mandelbaum & More 2015).”
Constraints on intrinsic alignment contamination of weak lensing surveys using the MegaZ-LRG sample (2010, methodology): “If Hirata & Seljak (2004), eq.”
Very weak lensing in the CFHTLS Wide: Cosmology from cosmic shear in the linear regime (2007, background): “In particular, the shear-shape correlation leads to an underestimation of σ8 (Hirata & Seljak 2004; Hirata et al. 2007).”
Potential sources of contamination to weak lensing measurements: constraints from N-body simulations (2006, background): “Hirata & Seljak (2004) explore two analytical models to estimate the magnitude of this effect finding that when galaxy ellipticity is quadratically related to the tidal or density field, as suggested by tidal torque theory, no shear-ellipticity correlation is found.”
CFHTLenS tomographic weak lensing cosmological parameter constraints: Mitigating the impact of intrinsic galaxy alignments (2013, methodology): “In this analysis we have assumed a simple one-parameter model that scales the amplitude of the II and GI intrinsic alignment contamination expected from a linear tidal field alignment model of galaxy shape correlation (Catelan et al. 2001; Hirata & Seljak 2004; Bridle & King 2007).”