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

Context. The data from the Euclid mission will enable the measurement of the angular positions and weak lensing shapes of over a billion galaxies, with their photometric redshifts obtained together with ground-based observations. This large dataset, with well-controlled systematic effects, will allow for cosmological analyses using the angular clustering of galaxies (GCph) and cosmic shear (WL). For Euclid, these two cosmological probes will not be independent because they will probe the same volume of the Universe. The cross-correlation (XC) between these probes can tighten constraints and is therefore important to quantify their impact for Euclid. Aims. In this study, we therefore extend the recently published Euclid forecasts by carefully quantifying the impact of XC not only on the final parameter constraints for different cosmological models, but also on the nuisance parameters. In particular, we aim to decipher the amount of additional information that XC can provide for parameters encoding systematic effects, such as galaxy bias, intrinsic alignments (IAs), and knowledge of the redshift distributions. Methods. We follow the Fisher matrix formalism and make use of previously validated codes. We also investigate a different galaxy bias model, which was obtained from the Flagship simulation, and additional photometric-redshift uncertainties; we also elucidate the impact of including the XC terms on constraining these latter. Results. Starting with a baseline model, we show that the XC terms reduce the uncertainties on galaxy bias by ∼17% and the uncertainties on IA by a factor of about four. The XC terms also help in constraining the γ parameter for minimal modified gravity models. Concerning galaxy bias, we observe that the role of the XC terms on the final parameter constraints is qualitatively the same irrespective of the specific galaxy-bias model used. For IA, we show that the XC terms can help in distinguishing between different models, and that if IA terms are neglected then this can lead to significant biases on the cosmological parameters. Finally, we show that the XC terms can lead to a better determination of the mean of the photometric galaxy distributions. Conclusions. We find that the XC between GCph and WL within the Euclid survey is necessary to extract the full information content from the data in future analyses. These terms help in better constraining the cosmological model, and also lead to a better understanding of the systematic effects that contaminate these probes. Furthermore, we find that XC significantly helps in constraining the mean of the photometric-redshift distributions, but, at the same time, it requires more precise knowledge of this mean with respect to single probes in order not to degrade the final “figure of merit”.

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Minimising the impact of scale-dependent galaxy bias on the joint cosmological analysis of large scale structures

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3810 ◽

2020 ◽

Author(s):

Marika Asgari ◽

Indiarose Friswell ◽

Mijin Yoon ◽

Catherine Heymans ◽

Andrej Dvornik ◽

...

Keyword(s):

Large Scale ◽

Cosmological Parameter ◽

Galaxy Surveys ◽

Large Scale Structures ◽

Non Linear ◽

Point Correlation ◽

Galaxy Bias ◽

New Statistics ◽

The Impact ◽

Parameter Constraints

Abstract We present a mitigation strategy to reduce the impact of non-linear galaxy bias on the joint ‘3 × 2pt’ cosmological analysis of weak lensing and galaxy surveys. The Ψ-statistics that we adopt are based on Complete Orthogonal Sets of E/B Integrals (COSEBIs). As such they are designed to minimize the contributions to the observable from the smallest physical scales where models are highly uncertain. We demonstrate that Ψ-statistics carry the same constraining power as the standard two-point galaxy clustering and galaxy-galaxy lensing statistics, but are significantly less sensitive to scale-dependent galaxy bias. Using two galaxy bias models, motivated by halo-model fits to data and simulations, we quantify the error in a standard 3 × 2pt analysis where constant galaxy bias is assumed. Even when adopting conservative angular scale cuts, that degrade the overall cosmological parameter constraints, we find of order 1σ biases for Stage III surveys on the cosmological parameter S8 = σ8(Ωm/0.3)α. This arises from a leakage of the smallest physical scales to all angular scales in the standard two-point correlation functions. In contrast, when analysing Ψ-statistics under the same approximation of constant galaxy bias, we show that the bias on the recovered value for S8 can be decreased by a factor of ∼2, with less conservative scale cuts. Given the challenges in determining accurate galaxy bias models in the highly non-linear regime, we argue that 3 × 2pt analyses should move towards new statistics that are less sensitive to the smallest physical scales.

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Estimating the impact of recombination uncertainties on the cosmological parameter constraints from cosmic microwave background experiments

Monthly Notices of the Royal Astronomical Society ◽

10.1111/j.1365-2966.2009.16136.x ◽

2010 ◽

Vol 403 (1) ◽

pp. 439-452 ◽

Cited By ~ 46

Author(s):

J. A. Rubiño-Martín ◽

J. Chluba ◽

W. A. Fendt ◽

B. D. Wandelt

Keyword(s):

Cosmic Microwave Background ◽

Cosmological Parameter ◽

Microwave Background ◽

The Impact ◽

Parameter Constraints

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Non-Gaussianity in the weak lensing correlation function likelihood – implications for cosmological parameter biases

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2948 ◽

2020 ◽

Vol 499 (2) ◽

pp. 2977-2993

Author(s):

Chien-Hao Lin ◽

Joachim Harnois-Déraps ◽

Tim Eifler ◽

Taylor Pospisil ◽

Rachel Mandelbaum ◽

...

Keyword(s):

Correlation Functions ◽

Principal Component ◽

Cosmological Parameter ◽

Weak Lensing ◽

Likelihood Model ◽

Point Correlation ◽

Parametric Functions ◽

Non Gaussian ◽

Parameter Constraints ◽

Skewness And Kurtosis

ABSTRACT We study the significance of non-Gaussianity in the likelihood of weak lensing shear two-point correlation functions, detecting significantly non-zero skewness and kurtosis in 1D marginal distributions of shear two-point correlation functions in simulated weak lensing data. We examine the implications in the context of future surveys, in particular LSST, with derivations of how the non-Gaussianity scales with survey area. We show that there is no significant bias in 1D posteriors of Ωm and σ8 due to the non-Gaussian likelihood distributions of shear correlations functions using the mock data (100 deg2). We also present a systematic approach to constructing approximate multivariate likelihoods with 1D parametric functions by assuming independence or more flexible non-parametric multivariate methods after decorrelating the data points using principal component analysis (PCA). While the use of PCA does not modify the non-Gaussianity of the multivariate likelihood, we find empirically that the 1D marginal sampling distributions of the PCA components exhibit less skewness and kurtosis than the original shear correlation functions. Modelling the likelihood with marginal parametric functions based on the assumption of independence between PCA components thus gives a lower limit for the biases. We further demonstrate that the difference in cosmological parameter constraints between the multivariate Gaussian likelihood model and more complex non-Gaussian likelihood models would be even smaller for an LSST-like survey. In addition, the PCA approach automatically serves as a data compression method, enabling the retention of the majority of the cosmological information while reducing the dimensionality of the data vector by a factor of ∼5.

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Cosmological parameter biases from Doppler-shifted weak lensing in stage IV experiments

Physical Review D ◽

10.1103/physrevd.103.123510 ◽

2021 ◽

Vol 103 (12) ◽

Author(s):

Anurag C. Deshpande ◽

Thomas D. Kitching

Keyword(s):

Stage Iv ◽

Cosmological Parameter ◽

Weak Lensing

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Blending and obscuration in weak lensing magnification

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab539 ◽

2021 ◽

Author(s):

E Gaztanaga ◽

S J Schmidt ◽

M D Schneider ◽

J A Tyson

Keyword(s):

Systematic Errors ◽

Weak Lensing ◽

Wide Field ◽

Photometric Redshifts ◽

Field Surveys ◽

Systematic Effects ◽

The Impact ◽

Close Pairs ◽

Mass Profiles

Abstract We test the impact of some systematic errors in weak lensing magnification measurements with the COSMOS 30-band photo-z Survey flux limited to Iauto < 25.0 using correlations of both source galaxy counts and magnitudes. Systematic obscuration effects are measured by comparing counts and magnification correlations. We use the ACS-HST catalogs to identify potential blending objects (close pairs) and perform the magnification analyses with and without blended objects. We find that blending effects start to be important (∼ 0.04 mag obscuration) at angular scales smaller than 0.1 arcmin. Extinction and other systematic obscuration effects can be as large as 0.10 mag (U-band) but are typically smaller than 0.02 mag depending on the band. After applying these corrections, we measure a 3.9σ magnification signal that is consistent for both counts and magnitudes. The corresponding projected mass profiles of galaxies at redshift z ≃ 0.6 (MI ≃ −21) is Σ = 25 ± 6M⊙h3/pc2 at 0.1 Mpc/h, consistent with NFW type profile with M200 ≃ 2 × 1012M⊙h/pc2. Tangential shear and flux-size magnification over the same lenses show similar mass profiles. We conclude that magnification from counts and fluxes using photometric redshifts has the potential to provide complementary weak lensing information in future wide field surveys once we carefully take into account systematic effects, such as obscuration and blending.

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Sufficiency of a Gaussian power spectrum likelihood for accurate cosmology from upcoming weak lensing surveys

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab522 ◽

2021 ◽

Author(s):

Robin E Upham ◽

Michael L Brown ◽

Lee Whittaker

Keyword(s):

Power Spectrum ◽

Random Noise ◽

Power Spectra ◽

Stage Iv ◽

Wishart Distribution ◽

Weak Lensing ◽

Dependence Structure ◽

Gaussian Fields ◽

Non Gaussian ◽

Parameter Constraints

Abstract We investigate whether a Gaussian likelihood is sufficient to obtain accurate parameter constraints from a Euclid-like combined tomographic power spectrum analysis of weak lensing, galaxy clustering and their cross-correlation. Testing its performance on the full sky against the Wishart distribution, which is the exact likelihood under the assumption of Gaussian fields, we find that the Gaussian likelihood returns accurate parameter constraints. This accuracy is robust to the choices made in the likelihood analysis, including the choice of fiducial cosmology, the range of scales included, and the random noise level. We extend our results to the cut sky by evaluating the additional non-Gaussianity of the joint cut-sky likelihood in both its marginal distributions and dependence structure. We find that the cut-sky likelihood is more non-Gaussian than the full-sky likelihood, but at a level insufficient to introduce significant inaccuracy into parameter constraints obtained using the Gaussian likelihood. Our results should not be affected by the assumption of Gaussian fields, as this approximation only becomes inaccurate on small scales, which in turn corresponds to the limit in which any non-Gaussianity of the likelihood becomes negligible. We nevertheless compare against N-body weak lensing simulations and find no evidence of significant additional non-Gaussianity in the likelihood. Our results indicate that a Gaussian likelihood will be sufficient for robust parameter constraints with power spectra from Stage IV weak lensing surveys.

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