[Paper Review] Designing Future Dark Energy Space Mission: I. Building Realistic Galaxy Spectro-Photometric Catalogs and their first applications

S. Jouvel, Jean‐Paul Kneib+13 more|arXiv (Cornell University)|Feb 4, 2009

Astronomy and Astrophysical Research44 citations

TL;DR

This paper presents two realistic, publicly available mock galaxy catalogs—based on the COSMOS survey and luminosity functions from GOODS—for designing future dark energy space missions. It demonstrates that extending spectroscopic surveys from 1–1.7µm to 0.6–1.7µm increases secure photometric redshift calibration to ~80% of galaxies, enabling high-precision weak-lensing tomography and BAO measurements critical for cosmology.

ABSTRACT

Future dark energy space missions such as JDEM and EUCLID are being designed to survey the galaxy population to trace the geometry of the universe and the growth of structure, which both depend on the cosmological model. To reach the goal of high precision cosmology they need to evaluate the capabilities of different instrument designs based on realistic mock catalog. The aim of this paper is to construct realistic and flexible mock catalogs based on our knowledge of galaxy population from current deep surveys. We explore two categories of mock catalog : (i) based on luminosity functions fit of observations (GOODS, UDF,COSMOS,VVDS) using the Le Phare software (ii) based on the observed COSMOS galaxy distribution which benefits from all the properties of the data-rich COSMOS survey. For these two catalogs, we have produced simulated number counts in several bands, color diagrams and redshift distribution for validation against real observational data. We also derive some basic requirements to help designing future Dark Energy mission in terms of number of galaxies available for the weak-lensing analysis as a function of the PSF size and depth of the survey. We also compute the spectroscopic success rate for future spectroscopic redshift surveys (i) aiming at measuring BAO in the case of the wide field spectroscopic redshift survey, and (ii) for the photometric redshift calibration survey which is required to achieve weak lensing tomography with great accuracy. They will be publicly accessible at http://lamwws.oamp.fr/cosmowiki/RealisticSpectroPhotCat, or by request to the first author of this paper.

Motivation & Objective

• To develop realistic, flexible mock galaxy catalogs that reflect current deep survey data for forecasting future dark energy mission performance.
• To evaluate the impact of survey depth, PSF size, and spectroscopic wavelength coverage on galaxy yield for weak lensing and BAO measurements.
• To determine optimal spectroscopic survey strategies for photometric redshift calibration and BAO detection in wide-field surveys.
• To validate the catalogs against real data (magnitude, color, redshift, size, emission-line distributions) to ensure reliability for mission design.

Proposed method

• Constructed the COSMOS Mock Catalog (CMC) using multiwavelength photometry (30 bands) and HST/ACS imaging to derive redshifts, SEDs, sizes, and emission-line strengths from the COSMOS field.
• Generated the GOODS Luminosity Function Catalog (GLFC) using Le Phare software with redshift-evolving Schechter luminosity functions fitted to GOODS, UDF, COSMOS, and VVDS data.
• Validated both catalogs by comparing simulated number counts, color diagrams, redshift distributions, and emission-line strengths against real survey data, accounting for selection functions.
• Used the catalogs to simulate spectroscopic success rates (SSR) for different redshift ranges and magnitude limits, assessing completeness for BAO and photometric redshift calibration.
• Evaluated the impact of PSF size and survey depth on the number of resolved galaxies for weak-lensings, distinguishing ground-based vs. space-based surveys.
• Modeled emission-line fluxes using VVDS-DEEP data to predict spectroscopic yield and assess completeness across galaxy types (ellipticals, spirals, starbursts).

Experimental results

Research questions

• RQ1 What is the optimal spectroscopic wavelength coverage to achieve >80% secure photometric redshift calibration for weak-lensing tomography?
• RQ2 How does the choice between ground-based and space-based spectroscopy affect the yield of spectroscopically confirmed galaxies in deep surveys?
• RQ3 To what extent can luminosity function-based and data-driven mock catalogs reproduce real survey observables like magnitude, color, and redshift distributions?
• RQ4 How do PSF size and survey depth jointly affect the number of resolved galaxies available for weak-lensing shape measurements?
• RQ5 What are the required survey depths and spectroscopic completeness levels to enable robust BAO and weak-lensing measurements in future dark energy missions?

Key findings

• Extending spectroscopic surveys from 1–1.7µm to 0.6–1.7µm increases the fraction of very secure spectroscopic redshifts to nearly 80% of galaxies, enabling highly accurate photometric redshift calibration.
• The CMC catalog reproduces observed magnitude, color, and redshift distributions with <20% discrepancies in number counts and 0.1–0.2 mag median color differences across 0.4–2.2µm bands.
• For weak-lensing tomography, a deep visible and near-infrared survey (I ~25.5) achieves a galaxy density of 60 galaxies per arcminute² with ~80% completeness for secure redshifts.
• Ground-based surveys are limited to resolved galaxies (I > 25) due to seeing-limited PSF, while space-based surveys can resolve fainter galaxies due to smaller PSF and deeper depth.
• A wide-field BAO survey using Hα emission can achieve a density of 4 galaxies per arcminute² for H < 22.5 in the redshift range 0.5 < z < 1.5.
• The GLFC enables forecasting deeper surveys than the CMC, but extrapolation in the near-infrared remains a significant uncertainty.