Euclid: impact of nonlinear prescriptions on cosmological parameter estimation from weak lensing cosmic shear

Euclid: impact of nonlinear prescriptions on cosmological parameter estimation from weak lensing cosmic shear


Abstract

Upcoming surveys will map the growth of large-scale structure with unprecented precision, improving our understanding of the dark sector of the Universe. Unfortunately, much of the cosmological information is encoded by the small scales, where the clustering of dark matter and the effects of astrophysical feedback processes are not fully understood. This can bias the estimates of cosmological parameters, which we study here for a joint analysis of mock Euclid cosmic shear and Planck cosmic microwave background data. We use different implementations for the modelling of the signal on small scales and find that they result in significantly different predictions. Moreover, the different nonlinear corrections lead to biased parameter estimates, especially when the analysis is extended into the highly nonlinear regime, with both the Hubble constant, H0, and the clustering amplitude, σ8, affected the most. Improvements in the modelling of nonlinear scales will therefore be needed if we are to resolve the current tension with more and better data. For a given prescription for the nonlinear power spectrum, using different corrections for baryon physics does not significantly impact the precision of Euclid, but neglecting these correction does lead to large biases in the cosmological parameters. In order to extract precise and unbiased constraints on cosmological parameters from Euclid cosmic shear data, it is therefore essential to improve the accuracy of the recipes that account for nonlinear structure formation, as well as the modelling of the impact of astrophysical processes that redistribute the baryons.

Effect of nonlinear prescriptions

 

Euclid preparation: VII. Forecast validation for Euclid cosmological probes

Euclid: impact of nonlinear prescriptions on cosmological parameter estimation from weak lensing cosmic shear


Abstract

Aims: The Euclid space telescope will measure the shapes and redshifts of galaxies to reconstruct the expansion history of the Universe and the growth of cosmic structures. The estimation of the expected performance of the experiment, in terms of predicted constraints on cosmological parameters, has so far relied on various individual methodologies and numerical implementations, which were developed for different observational probes and for the combination thereof. In this paper we present validated forecasts, which combine both theoretical and observational ingredients for different cosmological probes. This work is presented to provide the community with reliable numerical codes and methods for Euclid cosmological forecasts.
Methods: We describe in detail the methods adopted for Fisher matrix forecasts, which were applied to galaxy clustering, weak lensing, and the combination thereof. We estimated the required accuracy for Euclid forecasts and outline a methodology for their development. We then compare and improve different numerical implementations, reaching uncertainties on the errors of cosmological parameters that are less than the required precision in all cases. Furthermore, we provide details on the validated implementations, some of which are made publicly available, in different programming languages, together with a reference training-set of input and output matrices for a set of specific models. These can be used by the reader to validate their own implementations if required.
Results: We present new cosmological forecasts for Euclid. We find that results depend on the specific cosmological model and remaining freedom in each setting, for example flat or non-flat spatial cosmologies, or different cuts at non-linear scales. The numerical implementations are now reliable for these settings. We present the results for an optimistic and a pessimistic choice for these types of settings. We demonstrate that the impact of cross-correlations is particularly relevant for models beyond a cosmological constant and may allow us to increase the dark energy figure of merit by at least a factor of three.

 

Hybrid Pℓ(k): general, unified, non-linear matter power spectrum in redshift space

Hybrid Pℓ(k): general, unified, non-linear matter power spectrum in redshift space

 

Authors:

Journal:
Journal of Cosmology and Astroparticle Physics, Issue 09, article id. 001 (2020)
Year: 09/2020
Download: Inspire| Arxiv | DOI

Hybrid Pl(k): general, unified, non-linear matter power spectrum in redshift space


Abstract

Constraints on gravity and cosmology will greatly benefit from performing joint clustering and weak lensing analyses on large-scale structure data sets. Utilising non-linear information coming from small physical scales can greatly enhance these constraints. At the heart of these analyses is the matter power spectrum. Here we employ a simple method, dubbed "Hybrid Pl(k)", based on the Gaussian Streaming Model (GSM), to calculate the quasi non-linear redshift space matter power spectrum multipoles. This employs a fully non-linear and theoretically general prescription for the matter power spectrum. We test this approach against comoving Lagrangian acceleration simulation measurements performed in GR, DGP and f(R) gravity and find that our method performs comparably or better to the dark matter TNS redshift space power spectrum model {for dark matter. When comparing the redshift space multipoles for halos, we find that the Gaussian approximation of the GSM with a linear bias and a free stochastic term, N, is competitive to the TNS model.} Our approach offers many avenues for improvement in accuracy as well as further unification under the halo model.

Hybrid Pk

 

Euclid: Forecast constraints on the cosmic distance duality relation with complementary external probes

Euclid: impact of nonlinear prescriptions on cosmological parameter estimation from weak lensing cosmic shear


Abstract

In metric theories of gravity with photon number conservation, the luminosity and angular diameter distances are related via the Etherington relation, also known as the distance-duality relation (DDR). A violation of this relation would rule out the standard cosmological paradigm and point at the presence of new physics. We quantify the ability of Euclid, in combination with contemporary surveys, to improve the current constraints on deviations from the DDR in the redshift range 0<z<1.6. We start by an analysis of the latest available data, improving previously reported constraints by a factor of 2.5. We then present a detailed analysis of simulated Euclid and external data products, using both standard parametric methods (relying on phenomenological descriptions of possible DDR violations) and a machine learning reconstruction using Genetic Algorithms. We find that for parametric methods Euclid can (in combination with external probes) improve current constraints by approximately a factor of six, while for non-parametric methods Euclid can improve current constraints by a factor of three. Our results highlight the importance of surveys like Euclid in accurately testing the pillars of the current cosmological paradigm and constraining physics beyond the standard cosmological model.

Distance duality relation
2D contours on Ωm,0\Omega_{\rm m,0}Ωm,0​, ϵ0\epsilon_0ϵ0​ and ϵ1\epsilon_1ϵ1​, using currently available data for BAO (blue), SnIa (yellow) and the combination of the two (red). These results refer to the constant (top panel) and binned (central and bottom panels) ϵ(z)\epsilon(z)ϵ(z) cases.

 

CosmosClub: Ariel Sánchez (09/07/20)

CosmosClub Ariel Sánchez

Date: July 9th 2020, 10.00 a.m.

Speaker: Ariel Sánchez (MPE Garching/ Max-Planck-Institut für extraterrestrische Physik )

Title:   Let us bury the prehistoric h: arguments against using h1Mpc units in observational cosmology

Room: Zoom Meeting (connection details will be updated soon)

Abstract

It is common to express cosmological measurements in units of h^-1 Mpc. Here, we review some of the complications that originate from this practice. A crucial problem caused by these units is related to the normalization of the matter power spectrum, which is commonly characterized in terms of the linear-theory rms mass fluctuation in spheres of radius 8h^-1 Mpc, σ8. This parameter does not correctly capture the impact of h on the amplitude of density fluctuations. We show that the use of σ8 has caused critical misconceptions for both the so-called σ8 tension regarding the consistency between low-redshift probes and cosmic microwave background data, and the way in which growth-rate estimates inferred from redshift-space distortions are commonly expressed. We propose to abandon the use of h^1 Mpc units in cosmology and to characterize the amplitude of the matter power spectrum in terms of σ12, defined as the mass fluctuation in spheres of radius 12Mpc, whose value is similar to the standard σ8 for h0.67.

 

CosmosClub: Erwan Allys (02/07/20)

CosmosClub Erwan Allys

Date: July 2nd 2020, 10.00 a.m.

Speaker: Erwan Allys (ENS Paris / École Normale Supérieure, Laboratoire de Radioastronomie )

Title:   The Wavelet Phase Harmonics, a new interpretable statistical description for analysis and synthesis of the LSS

Room: Zoom Meeting (connection details will be updated soon)

Abstract

The statistical characterization of non-Gaussian fields is a major problem in current astrophysics, and no method has clearly emerged up to now to do so. In this presentation, I will introduce the Wavelet Phase Harmonics (WPH), a low-dimensional and interpretable set of statistics that efficiently characterizes the couplings between scales in non-linear processes. This description, that has been recently introduced in data science, is inspired from neural networks. Applied to projected matter density field from Quijote N-body Large Scale Structure (LSS) simulations, I will show how the WPH are able to provide better constraints on five cosmological parameters than the joint power spectrum and bispectrum, as well as to produce new realistic statistical syntheses from a maximum-entropy model. These results open the path to the use of a new type of statistical description for non-Gaussian fields in astrophysics.

 

Cosmology with Python wrappers for Einstein-Boltzmann Codes

This tutorial is comprised of a series of Jupyter notebooks with simple demonstrations and exercises on how to use CAMB and CLASS using python wrappers. The code is designed for non-experts in the field, therefore it includes relatively simple explanations of cosmological concepts. It intends to show a general overview of the things that are possible with Einstein-Boltzmann codes and python.

Euclid: The importance of galaxy clustering and weak lensing cross-correlations within the photometric Euclid survey

Euclid: impact of nonlinear prescriptions on cosmological parameter estimation from weak lensing cosmic shear


Abstract

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".

XC importance
Ratio of the errors on Δzi\Delta z_iΔzi​ without and with the inclusion of XC. Yellow and red lines refer to the pessimistic and optimistic scenario.

 

Emulators for the nonlinear matter power spectrum beyond ΛCDM

Emulators for the nonlinear matter power spectrum beyond ΛCDM

 

Authors:

Winther, Hans A.; Casas, Santiago; Baldi, Marco; Koyama, Kazuya; Li, Baojiu; Lombriser, Lucas; Zhao, Gong-Bo 

Journal:
Physical Review D, Volume 100, Issue 12, article id.123540
Year: 12/2019
Download: Inspire| Arxiv


Abstract

Accurate predictions for the nonlinear matter power spectrum are needed to confront theory with observations in current and near future weak-lensing and galaxy clustering surveys. We propose a computationally cheap method to create an emulator for modified gravity models by utilizing existing emulators for Λ CDM . Using a suite of N -body simulations, we construct a fitting function for the enhancement of both the linear and nonlinear matter power spectrum in the commonly studied Hu-Sawicki f (R ) gravity model valid for wave numbers k ≲5 - 10 h Mpc-1 and redshifts z ≲3 . We show that the cosmology dependence of this enhancement is relatively weak so that our fit, using simulations coming from only one cosmology, can be used to get accurate predictions for other cosmological parameters. We also show that the cosmology dependence can, if needed, be included by using linear theory, approximate N -body simulations (such as comoving lagrangian acceleration) and semianalytical tools like the halo model. Our final fit can easily be combined with any emulator or semianalytical models for the nonlinear Λ CDM power spectrum to accurately, and quickly, produce a nonlinear power spectrum for this particular modified gravity model. The method we use can be applied to fairly cheaply construct an emulator for other modified gravity models. As an application of our fitting formula, we use it to compute Fisher forecasts for how well galaxy clustering and weak lensing in a Euclid-like survey will be at constraining modifications of gravity.

Fitting formula

 

Measuring Gravity at Cosmological Scales

Measuring Gravity at Cosmological Scales

 

Authors:  Luca Amendola , Dario Bettoni, Ana Marta Pinho Santiago Casas,
Journal: Review Paper
Year: 02/2019
Download: Inspire| Arxiv


Abstract

This paper is a pedagogical introduction to models of gravity and how to constrain them through cosmological observations. We focus on the Horndeski scalar-tensor theory and on the quantities that can be measured with a minimum of assumptions. Alternatives or extensions of General Relativity have been proposed ever since its early years. Because of Lovelock theorem, modifying gravity in four dimensions typically means adding new degrees of freedom. The simplest way is to include a scalar field coupled to the curvature tensor terms. The most general way of doing so without incurring in the Ostrogradski instability is the Horndeski Lagrangian and its extensions. Testing gravity means therefore, in its simplest term, testing the Horndeski Lagrangian. Since local gravity experiments can always be evaded by assuming some screening mechanism or that baryons are decoupled, or even that the effects of modified gravity are visible only at early times, we need to test gravity with cosmological observations in the late universe (large-scale structure) and in the early universe (cosmic microwave background). In this work we review the basic tools to test gravity at cosmological scales, focusing on model-independent measurements.

logfsigma8