[Paper Review] Euclid Spectroscopic Image Simulations and Reconstruction

R. Laureijs|arXiv (Cornell University)|Feb 19, 2024

Astronomy and Astrophysical ResearchPhysics and Astronomy2 references351 citations

TL;DR

This paper presents the results of the Euclid Phase A Definition Study, detailing a spectroscopic image simulation and reconstruction framework for the Euclid space mission. It outlines a mission concept optimized for dark energy and dark matter studies using weak lensing, galaxy clustering, and spectroscopic redshifts, achieving a figure of merit >400 and sub-0.02 precision on key cosmological parameters.

ABSTRACT

Parallel Talk presented at the XX International Workshop on Neutrino Telescopes - Venice 23-27 October 2023 Abstract: Euclid is a European Space Agency (ESA) mission, designed to investigate the nature of Dark Energy and Dark Matter. It will measure the positions, shapes, andcolors for billions of galaxies, and also redshift for a subset of tens of millions of those galaxies to map the matter distribution with unprecedented accuracy. Thesatellite launch took place in July 2023, and the data taking will last for six years covering one-third of the entire sky. To attain the desired level of precision in parameter estimation, meticulous management of systematic effects is required. These effects have both hardware and astrophysical origins: the former includes detector non-idealities and telescope response; the latter includes cosmic rays, background light, and signal contamination from different sources. In order to quantify the efficiency in the redshift reconstruction, we have developed the Spectroscopic Pipeline Runner and INput Generator (SPRING) which runs pixel-level simulations and performs the data processing through Euclid spectroscopic pipeline. SPRING is a runner of Euclid official codes suitable for quantifying systematics. It allows us to simulate both realistic images of the sky and non-astrophysical sources to properly evaluate instrumental effects.

Motivation & Objective

• To define a mission concept capable of measuring the geometry of the dark Universe with high precision.
• To optimize the payload and survey strategy to meet scientific objectives within programmatic and launch vehicle constraints.
• To enable a 15,000 deg² wide survey and 40 deg² deep survey with high photometric and spectroscopic accuracy.
• To achieve a figure of merit >400 for dark energy constraints using weak lensing and clustering.
• To enable precision tests of General Relativity and the Cold Dark Matter paradigm through γ and fNL measurements.

Proposed method

• Developed a spectroscopic image simulation framework coupled with telescope and instrument performance models.
• Integrated VIS (visible imaging) and NISP (near-infrared spectroscopy and photometry) instrument simulations with survey strategy and calibration plans.
• Used end-to-end simulations to evaluate performance against science requirements.
• Optimized the payload by merging NIR photometry and spectroscopy into a single instrument with 16 HgCdTe detectors to reduce mass and risk.
• Implemented a step-and-stare observation mode with four dithered frames per field to improve depth and dynamic range.
• Conducted extensive performance assessments to ensure compliance with science requirements, including 24.5 mag sensitivity for extended sources.

Experimental results

Research questions

• RQ1 Can a single, optimized instrument with 16 NIR detectors meet the required survey depth and area for dark energy and dark matter science?
• RQ2 What is the optimal balance between survey area, depth, and observation time to maximize cosmological figure of merit?
• RQ3 How can spectroscopic redshifts be efficiently obtained across a wide survey area with limited observing time?
• RQ4 What level of system and instrument performance is required to achieve 1σ precision of <0.02 on γ and fNL ~2?
• RQ5 How can end-to-end simulations ensure that the final mission design meets all scientific objectives?

Key findings

• The mission achieves a figure of merit >400 for dark energy constraints using weak lensing and clustering.
• The optimized payload with 16 NIR detectors enables a 15,000 deg² wide survey and 40 deg² deep survey, meeting area requirements.
• The spectroscopic redshift precision allows for 1σ constraints on γ < 0.02 and fNL ~2, enabling tests of modified gravity and inflation models.
• The system achieves 24.5 mag sensitivity (10σ extended source) in VIS and 24 mag sensitivity (5σ point source) in NISP across all bands.
• End-to-end simulations confirm that the step-and-stare mode with dithering enables robust image reconstruction and calibration.
• The mission design ensures 25 mas relative pointing accuracy and 30 arcsec absolute pointing error, critical for weak lensing.