A CLIPPING METHOD TO MITIGATE THE IMPACT OF CATASTROPHIC PHOTOMETRIC REDSHIFT ERRORS ON WEAK LENSING TOMOGRAPHY

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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Cosmological consequences of intrinsic alignments supersample covariance

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3214 ◽

2020 ◽

Vol 499 (4) ◽

pp. 6094-6104

Author(s):

Saeed Ansarifard ◽

S M S Movahed

Keyword(s):

Signal To Noise Ratio ◽

Cosmological Parameters ◽

Parameters Estimation ◽

Weak Lensing ◽

Matrix Formalism ◽

Photometric Redshift ◽

High Multipoles ◽

Cosmic Shear ◽

The Impact ◽

Gravitational Weak Lensing

ABSTRACT We examine cosmological constraints from high-precision weak-lensing surveys including supersample covariance (SSC) due to the finite survey volume. Specifically, we focus on the contribution of beat coupling in the intrinsic alignments as a part of full cosmic shear signal under flat-sky approximation. The SSC-effect grows by going to lower redshift bin and indicates considerable footprint on the intermediate and high multipoles for cumulative signal-to-noise ratio (SNR). The SNR is reduced by $\approx 10{{\ \rm per\ cent}}$ as a consequence of including the intrinsic alignment SSC, for the full cosmic shear signal, depending on the amplitude of intrinsic alignments, the ellipticity dispersion, and the survey redshift ranges, while the contribution of photometric redshift error can be ignored in the cumulative SNR. Using the Fisher-matrix formalism, we find that the impact of large modes beyond the volume of the surveys on the small modes alters the intrinsic alignments. However, corresponding impact on the cosmological parameters’ estimation is marginal compared to that of for gravitational weak lensing, particularly, when all available redshift bins are considered. Our results also demonstrate that including SSC-effect on the intrinsic alignments in the analytical covariance matrix of full cosmic shear leads to increase marginally the confidence interval for σ8 by $\approx 10{{\ \rm per\ cent}}$ for a sample with almost high intrinsic alignment amplitude.

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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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The impact of cosmic variance on simulating weak lensing surveys

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stv520 ◽

2015 ◽

Vol 449 (4) ◽

pp. 3597-3612 ◽

Cited By ~ 5

Author(s):

Arun Kannawadi ◽

Rachel Mandelbaum ◽

Claire Lackner

Keyword(s):

Weak Lensing ◽

The Impact

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Weak-lensing clusters from HSC survey first-year data: Mitigating the dilution effect of foreground and cluster-member galaxies

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa068 ◽

2020 ◽

Vol 72 (5) ◽

Cited By ~ 1

Author(s):

Takashi Hamana ◽

Masato Shirasaki ◽

Yen-Ting Lin

Keyword(s):

Dilution Effect ◽

Weak Lensing ◽

First Year ◽

Cluster Member ◽

The Public ◽

Photometric Redshift ◽

Source Sample ◽

Strategic Program ◽

Dilution Effects ◽

Cross Match

Abstract We present a weak-lensing cluster search using Hyper Suprime-Cam Subaru Strategic Program (HSC survey) first-year data. We pay special attention to the dilution effect of cluster-member and foreground galaxies on weak-lensing signals from clusters of galaxies; we adopt the globally normalized weak-lensing estimator which is least affected by cluster-member galaxies, and we select source galaxies by using photometric redshift information to mitigate the effect of foreground galaxies. We produce six samples of source galaxies with different low-z galaxy cuts, construct weak-lensing mass maps for each source sample, and search for high peaks in the mass maps that cover an effective survey area of ∼120 deg2. We combine six catalogs of high peaks into a sample of cluster candidates which contains 124 high peaks with signal-to-noise ratios greater than five. We cross-match the peak sample with the public optical cluster catalog constructed from the same HSC survey data to identify cluster counterparts of the peaks. We find that 107 out of 124 peaks have matched clusters within 5′ of peak positions. Among them, we define a subsample of 64 secure clusters that we use to examine dilution effects on our weak-lensing cluster search. We find that source samples with low-z galaxy cuts mitigate the dilution effect on weak-lensing signals of high-z clusters ($z \gtrsim 0.3$), and thus combining multiple peak catalogs from different source samples improves the efficiency of weak-lensing cluster searches.

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Separating the intrinsic alignment signal and the lensing signal using self-calibration in photo-z surveys with KiDS450 and KV450 Data

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1354 ◽

2020 ◽

Vol 495 (4) ◽

pp. 3900-3919 ◽

Cited By ~ 3

Author(s):

Ji Yao ◽

Eske M Pedersen ◽

Mustapha Ishak ◽

Pengjie Zhang ◽

Anish Agashe ◽

...

Keyword(s):

Full Potential ◽

Photometric Redshift ◽

Self Calibration ◽

Intrinsic Shape ◽

Best Fitting ◽

Systematic Biases ◽

Cosmic Shear ◽

Validation Tests ◽

The Impact ◽

Best Fit

ABSTRACT To reach the full potential for the next generation of weak lensing surveys, it is necessary to mitigate the contamination of intrinsic alignments (IAs) of galaxies in the observed cosmic shear signal. The self-calibration (SC) of IAs provides an independent method to measure the IA signal from the survey data and the photometric redshift information. It operates differently from the marginalization method based on the IA modelling. In this work, we present the first application of SC to the KiDS450 data and the KV450 data, to split directly the intrinsic shape–galaxy density (Ig) correlation signal and the gravitational shear–galaxy density (Gg) correlation signal, using the information from photometric redshift (photo-z). We achieved a clear separation of the two signals and performed several validation tests. Our measured signals are found to be in general agreement with the KiDS450 cosmic shear best-fitting cosmology, for both lensing and IA measurements. For KV450, we use partial (high-z) data, and our lensing measurements are also in good agreement with KV450 cosmic shear best fit, while our IA signal suggests a larger IA amplitude for the high-z sample. We discussed the impact of photo-z quality on IA detection and several other potential systematic biases. Finally, we discuss the potential application of the information extracted for both the lensing signal and the IA signal in future surveys.

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Impact of Weak Lensing Mass Calibration on eROSITA Galaxy Cluster Cosmological Studies – a Forecast

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz1778 ◽

2019 ◽

Cited By ~ 4

Author(s):

S Grandis ◽

J J Mohr ◽

J P Dietrich ◽

S Bocquet ◽

A Saro ◽

...

Keyword(s):

Count Rate ◽

Galaxy Cluster ◽

Effective Area ◽

Mass Scale ◽

Weak Lensing ◽

Parameter Uncertainties ◽

X Ray ◽

Mass Scaling ◽

Mass Calibration ◽

The Impact

Abstract We forecast the impact of weak lensing (WL) cluster mass calibration on the cosmological constraints from the X-ray selected galaxy cluster counts in the upcoming eROSITA survey. We employ a prototype cosmology pipeline to analyze mock cluster catalogs. Each cluster is sampled from the mass function in a fiducial cosmology and given an eROSITA count rate and redshift, where count rates are modeled using the eROSITA effective area, a typical exposure time, Poisson noise and the scatter and form of the observed X-ray luminosity– and temperature–mass–redshift relations. A subset of clusters have mock shear profiles to mimic either those from DES and HSC or from the future Euclid and LSST surveys. Using a count rate selection, we generate a baseline cluster cosmology catalog that contains 13k clusters over 14,892 deg2 of extragalactic sky. Low mass groups are excluded using raised count rate thresholds at low redshift. Forecast parameter uncertainties for ΩM, σ8 and w are 0.023 (0.016; 0.014), 0.017 (0.012; 0.010), and 0.085 (0.074; 0.071), respectively, when adopting DES+HSC WL (Euclid; LSST), while marginalizing over the sum of the neutrino masses. A degeneracy between the distance–redshift relation and the parameters of the observable–mass scaling relation limits the impact of the WL calibration on the w constraints, but with BAO measurements from DESI an improved determination of w to 0.043 becomes possible. With Planck CMB priors, ΩM (σ8) can be determined to 0.005 (0.007), and the summed neutrino mass limited to ∑mν < 0.241 eV (at 95%). If systematics on the group mass scale can be controlled, the eROSITA group and cluster sample with 43k objects and LSST WL could constrain ΩM and σ8 to 0.007 and w to 0.050.

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