[Paper Review] Dark Energy Survey Year 3 Results: Deep Field Optical + Near-Infrared Images and Catalogue

W G Hartley, A. Choi+116 more|arXiv (Cornell University)|Dec 23, 2020

Galaxies: Formation, Evolution, Phenomena132 references67 citations

TL;DR

This paper presents the Dark Energy Survey Year 3 Deep Fields, a multi-wavelength (𝑢𝑔𝑟𝑖𝑧𝐽𝐻𝐾𝑠) catalogue of 2.8 million sources across 5.88 square degrees in four high-depth fields, using co-added DECam and VISTA imaging. The study introduces a novel model-fitting photometry pipeline with tight PSF control and consistent astrometry, achieving excellent photometric redshift performance (NMAD = 0.023 at 𝑖 < 23), enabling precise cosmological calibration for weak lensing and galaxy clustering analyses.

ABSTRACT

We describe the Dark Energy Survey (DES) Deep Fields, a set of images and associated multi-wavelength catalogue ($ugrizJHKs$) built from Dark Energy Camera (DECam) and Visible and Infrared Survey Telescope for Astronomy (VISTA) data. The DES Deep Fields comprise 11 fields (10 DES supernova fields plus COSMOS), with a total area of $\sim30~$ square degrees in $ugriz$ bands and reaching a maximum $i$-band depth of 26.75 (AB, $10\sigma$, 2 arcsec). We present a catalogue for the DES 3-year cosmology analysis of those four fields with full 8-band coverage, totalling $5.88~$ sq. deg. after masking. Numbering $2.8~$million objects ($1.6~$million post masking), our catalogue is drawn from images coadded to consistent depths of $r=25.7, i=25, z=24.3$ mag. We use a new model-fitting code, built upon established methods, to deblend sources and ensure consistent colours across the $u$-band to $Ks$-band wavelength range. We further detail the tight control we maintain over the point-spread function modelling required for the model fitting, astrometry and consistency of photometry between the four fields. The catalogue allows us to perform a careful star-galaxy separation and produces excellent photometric redshift performance (${ m NMAD} = 0.023$ at $i<23$). The Deep-Fields catalogue will be made available as part of the cosmology data products release, following the completion of the DES 3-year weak lensing and galaxy clustering cosmology work.

Motivation & Objective

• To produce a high-fidelity, multi-wavelength catalogue from co-added optical and near-infrared imaging for cosmological calibration in the DES Year 3 analysis.
• To minimize systematic uncertainties in photometry, astrometry, and PSF modeling across deep fields to enable precise weak lensing and galaxy clustering measurements.
• To achieve robust star-galaxy separation and high-accuracy photometric redshifts using a model-fitting pipeline with consistent depth and PSF control across 𝑢 to 𝐾𝑠 bands.
• To create a legacy data product that supports future cosmological analyses by extending coverage and depth beyond the main survey.

Proposed method

• Co-added deep imaging from DES DECam (𝑢𝑔𝑟𝑖𝑧) and VISTA (𝐽𝐻𝐾𝑠) in 11 fields, with four fields achieving full 8-band coverage.
• Applied a new model-fitting photometry code based on established methods to deblend sources and ensure consistent colors across the full wavelength range.
• Implemented rigorous PSF modeling with sub-0.1′′ accuracy to minimize systematic errors in photometry and shear measurement.
• Used SCAMP and SWarp for astrometric and image co-addition calibration, ensuring consistent astrometry across fields.
• Applied a data-driven prior on galaxy light profiles to improve shear measurement accuracy in weak lensing pipelines.
• Validated photometric redshift performance using NMAD metric, achieving 0.023 at 𝑖 < 23.

Experimental results

Research questions

• RQ1 How can multi-wavelength imaging from optical to near-infrared be co-added and calibrated to achieve consistent photometry across deep fields with minimal systematics?
• RQ2 What level of photometric redshift accuracy can be achieved with model-fitting photometry in a deep, multi-band survey with consistent PSF control?
• RQ3 How does the inclusion of near-infrared data improve the fidelity of galaxy catalogues and photometric redshifts in high-redshift cosmological studies?
• RQ4 To what extent can the Deep Fields catalogue serve as a calibration reference for the main DES survey’s weak lensing and clustering measurements?
• RQ5 What is the optimal strategy for extending the Deep Fields to wider area and deeper depth while maintaining photometric consistency?

Key findings

• The catalogue contains 2.8 million sources (1.6 million after masking), with 5.88 square degrees of full 8-band coverage (𝑢𝑔𝑟𝑖𝑧𝐽𝐻𝐾𝑠), co-added to consistent depths of 𝑟 = 25.7, 𝑖 = 25.0, 𝑧 = 24.3 mag.
• Photometric redshift performance reaches an NMAD of 0.023 at 𝑖 < 23, indicating high fidelity in redshift estimation.
• The PSF modeling is tightly controlled, with sub-0.1′′ accuracy in the 𝑟𝑖𝑧 bands, critical for weak lensing shear measurement.
• The model-fitting pipeline enables consistent deblending and color measurement across the 𝑢-band to 𝐾𝑠-band range, reducing photometric systematics.
• The catalogue supports the DES Y3 cosmology analysis by providing a high-dimensional self-organizing map (SOM) and transfer function calibration.
• The data are publicly released as part of the DES cosmology data products, with future extensions planned to include deeper coadds and additional SN fields.