Category: Galaxy clustering

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

Posted on by Valeria Pettorino

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

 

Authors:
Journal:
 
Year: 10/2020
Download: Inspire| Arxiv

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 preparation: VII. Forecast validation for Euclid cosmological probes

Posted on by Valeria Pettorino

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

 

Authors:
Journal:
Astronomy & Astrophysics, Volume 642, id.A191, 66 pp.
Year: 10/2020
Download: Inspire| Arxiv

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

Posted on by Valeria Pettorino

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

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

Posted on by Valeria Pettorino

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

 

Authors:
Journal:
 
Astronomy & Astrophysics, Volume 643, id.A70, 17 pp.
Year: 11/2020
Download: Inspire| Arxiv | DOI

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

Posted on by Valeria Pettorino

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

 

The DESI Experiment Part I: Science,Targeting, and Survey Design

The DESI Experiment Part I: Science,Targeting, and Survey Design

Posted on by Martin Kilbinger

 

Authors: DESI collaboration
Journal: ArXiv
Year: 2016
Download: ADS | arXiv

 

Abstract

DESI (Dark Energy Spectroscopic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. To trace the underlying dark matter distribution, spectroscopic targets will be selected in four classes from imaging data. We will measure luminous red galaxies up to $z=1.0$. To probe the Universe out to even higher redshift, DESI will target bright [O II] emission line galaxies up to $z=1.7$. Quasars will be targeted both as direct tracers of the underlying dark matter distribution and, at higher redshifts ($ 2.1 < z < 3.5$), for the Ly-$\alpha$ forest absorption features in their spectra, which will be used to trace the distribution of neutral hydrogen. When moonlight prevents efficient observations of the faint targets of the baseline survey, DESI will conduct a magnitude-limited Bright Galaxy Survey comprising approximately 10 million galaxies with a median $z\approx 0.2$. In total, more than 30 million galaxy and quasar redshifts will be obtained to measure the BAO feature and determine the matter power spectrum, including redshift space distortions.

 

 

The DESI Experiment Part II: Instrument Design

The DESI Experiment Part II: Instrument Design

Posted on by Martin Kilbinger

 

Authors: DESI collaboration
Journal: ArXiv
Year: 2016
Download: ADS | arXiv

 

Abstract

DESI (Dark Energy Spectropic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. The DESI instrument is a robotically-actuated, fiber-fed spectrograph capable of taking up to 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm. The fibers feed ten three-arm spectrographs with resolution
R=λ/ΔλR= λ/Δλ
 between 2000 and 5500, depending on wavelength. The DESI instrument will be used to conduct a five-year survey designed to cover 14,000 deg
2^2
. This powerful instrument will be installed at prime focus on the 4-m Mayall telescope in Kitt Peak, Arizona, along with a new optical corrector, which will provide a three-degree diameter field of view. The DESI collaboration will also deliver a spectroscopic pipeline and data management system to reduce and archive all data for eventual public use.

 

 

CFHTLenS: weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment

CFHTLenS: weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment

Posted on by Martin Kilbinger
Authors: T. Schrabback et al.
Journal: MNRAS
Year: 2015
Download: ADS | arXiv

Abstract

We present weak lensing constraints on the ellipticity of galaxy-scale matter haloes and the galaxy-halo misalignment. Using data from the Canada-France-Hawaii Telescope Lensing Survey (CFHTLenS), we measure the weighted-average ratio of the aligned projected ellipticity components of galaxy matter haloes and their embedded galaxies,
fhf_\mathrm{h}
, split by galaxy type. We then compare our observations to measurements taken from the Millennium Simulation, assuming different models of galaxy-halo misalignment. Using the Millennium Simulation we verify that the statistical estimator used removes contamination from cosmic shear. We also detect an additional signal in the simulation, which we interpret as the impact of intrinsic shape-shear alignments between the lenses and their large-scale structure environment. These alignments are likely to have caused some of the previous observational constraints on
fhf_\mathrm{h}
 to be biased high. From CFHTLenS we find
fh=−0.04±0.25f_\mathrm{h}=-0.04 \pm 0.25
 for early-type galaxies, which is consistent with current models for the galaxy-halo misalignment predicting
fh≃0.20f_\mathrm{h}\simeq 0.20
. For late-type galaxies we measure
fh=0.69−0.36+0.37f_\mathrm{h}=0.69_{-0.36}^{+0.37}
 from CFHTLenS. This can be compared to the simulated results which yield
fh≃0.02f_\mathrm{h}\simeq 0.02
 for misaligned late-type models.

The galaxy-halo connection from a joint lensing, clustering and abundance analysis in the CFHTLenS/VIPERS field

The galaxy-halo connection from a joint lensing, clustering and abundance analysis in the CFHTLenS/VIPERS field

Posted on by Martin Kilbinger
Authors: J. Coupon et al.
Journal: MNRAS
Year: 2015
Download: ADS | arXiv

Abstract

We present new constraints on the relationship between galaxies and their host dark matter halos, measured from the location of the peak of the stellar-to-halo mass ratio (SHMR), up to the most massive galaxy clusters at redshift
z∼0.8z\sim0.8
 and over a volume of nearly 0.1~Gpc
3^3
. We use a unique combination of deep observations in the CFHTLenS/VIPERS field from the near-UV to the near-IR, supplemented by
∼60000\sim60\,000
 secure spectroscopic redshifts, analysing galaxy clustering, galaxy-galaxy lensing and the stellar mass function. We interpret our measurements within the halo occupation distribution (HOD) framework, separating the contributions from central and satellite galaxies. We find that the SHMR for the central galaxies peaks at
Mh,peak=1.9−0.1+0.2×1012M⊙M_{\rm h, peak} = 1.9^{+0.2}_{-0.1}\times10^{12} M_{\odot}
 with an amplitude of
0.0250.025
, which decreases to
∼0.001\sim0.001
 for massive halos (
Mh>1014M⊙M_{\rm h} > 10^{14} M_{\odot}
). Compared to central galaxies only, the total SHMR (including satellites) is boosted by a factor 10 in the high-mass regime (cluster-size halos), a result consistent with cluster analyses from the literature based on fully independent methods. After properly accounting for differences in modelling, we have compared our results with a large number of results from the literature up to
z=1z=1
: we find good general agreement, independently of the method used, within the typical stellar-mass systematic errors at low to intermediate mass (
M⋆<1011M⊙{M}_{\star} < 10^{11} M_{\odot}
) and the statistical errors above. We have also compared our SHMR results to semi-analytic simulations and found that the SHMR is tilted compared to our measurements in such a way that they over- (under-) predict star formation efficiency in central (satellite) galaxies.