[Paper Review] Euclid: performance on main cosmological parameter science

I. Tutusaus, Jenny G. Sorce+1 more|arXiv (Cornell University)|Nov 16, 2022

Galaxies: Formation, Evolution, Phenomena17 references4 citations

TL;DR

This paper evaluates Euclid's performance in constraining cosmological parameters using its planned photometric and spectroscopic surveys. By combining galaxy clustering and weak gravitational lensing measurements, Euclid is expected to constrain the dark energy equation of state to 3%, improving current constraints by a factor of three through end-to-end simulations and systematic error modeling.

ABSTRACT

Euclid will observe 15 000 deg$^2$ of the darkest sky, in regions free of contamination by light from our Galaxy and our Solar System. Three "Euclid Deep Fields" surveys covering around 40 deg$^2$ in total will extend the scientific scope of the mission to the high-redshift Universe. The complete survey will be constituted by hundreds of thousands of images and several tens of petabytes of data. About 10 billion sources will be observed. With these images Euclid will probe the expansion history of the Universe and the evolution of cosmic structures. This will be achieved by measuring the effect on galaxy shapes due to dark matter gravitational lensing, and by reconstructing the three-dimensional distribution of cosmic structures from the measured spectroscopic redshifts of galaxies and clusters of galaxies. These proceedings present the implications for cosmology and cosmological constraints of this unprecedented data set. Of particular interest are the expected constraints on the nature of dark energy.

Motivation & Objective

• To assess Euclid’s expected performance in constraining key cosmological parameters, especially dark energy.
• To evaluate the impact of systematic uncertainties on cosmological inference using end-to-end simulation pipelines.
• To validate that the mission’s combined photometric and spectroscopic surveys can recover the input cosmology despite realistic observational effects.
• To prepare robust data analysis pipelines for real Euclid data, including modeling non-linearities and relativistic effects.
• To demonstrate that combining multiple cosmological probes (galaxy clustering and weak lensing) breaks parameter degeneracies and enhances constraining power.

Proposed method

• End-to-end simulation pipelines were developed to generate mock raw images from the Flagship simulation, incorporating astrophysical foregrounds and survey patterns.
• For spectroscopic data, a full reduction pipeline processes mock images to produce final catalogs for cosmological inference.
• For photometric data, systematic effects (e.g., point spread function, detector noise) were applied analytically post-simulation to compare perturbed vs. unperturbed catalogs.
• Summary statistics such as the matter power spectrum and correlation functions were measured on both mock catalogs to extract cosmological constraints.
• Cosmological inference was performed to test whether the input cosmology could be recovered, validating pipeline robustness.
• Emulators and improved modeling of non-linear effects and relativistic corrections were developed to accelerate and refine analysis.

Experimental results

Research questions

• RQ1 Can Euclid’s combined photometric and spectroscopic surveys recover the input cosmology in the presence of realistic systematics?
• RQ2 What level of precision can Euclid achieve in constraining the dark energy equation of state?
• RQ3 How do systematic uncertainties in photometric redshifts and shape measurements affect cosmological parameter inference?
• RQ4 To what extent do combining galaxy clustering and weak lensing probes break degeneracies between cosmological parameters?
• RQ5 How effective are end-to-end simulation pipelines in validating the performance of Euclid’s data analysis chain?

Key findings

• Euclid is expected to constrain the dark energy equation of state to 3%, representing a threefold improvement over current constraints.
• The combination of photometric and spectroscopic galaxy clustering with weak lensing significantly enhances parameter constraints by breaking degeneracies.
• End-to-end simulations confirm that the cosmological input can be recovered, validating the robustness of the analysis pipelines.
• Systematic uncertainties in photometric surveys—particularly at small scales—are effectively modeled and controlled through analytical perturbation techniques.
• The development of emulators and improved non-linear modeling ensures efficient and accurate cosmological inference from the full data set.
• The mission’s design enables unprecedented constraints on dark matter, gravity, and dark energy, surpassing all current observations combined.