Euclid Quick Data Release (Q1): VIS processing and data products

TL;DR

The paper presents the VIS Processing Function (VIS PF) for Euclid, detailing pixel-level corrections, astrometric/photometric calibrations, and stacking/catalog extraction to deliver science-ready VIS data. It demonstrates that, during Performance Verification and the Q1 data release, image quality, astrometric accuracy, and photometric calibration meet pre-launch specifications, with a stable FWHM around a few tenths of an arcsecond and photometric scatter below 1%. The pipeline combines per-quadrant calibration with cross-field astrometric references (Gaia DR3) and Gaia-driven photometric zeropoints, producing MEF-frame data products and catalogues suitable for weak-lensing analyses. While CTI corrections were not applied in Q1, ongoing monitoring and future updates are planned to further improve accuracy as the radiation environment evolves. The Q1 results underscore the VIS PF’s capability to generate a high-quality, wide-area, high-resolution VIS atlas, enabling robust galaxy counts, accurate astrometry, and precise photometry across the Euclid sky.

Abstract

This paper describes the VIS Processing Function (VIS PF) of the Euclid ground segment pipeline, which processes and calibrates raw data from the VIS camera. We present the algorithms used in each processing element, along with a description of the on-orbit performance of VIS PF, based on Performance Verification (PV) and Q1 data. We demonstrate that the principal performance metrics (image quality, astrometric accuracy, photometric calibration) are within pre-launch specifications. The image-to-image photometric scatter is less than $0.8\%$, and absolute astrometric accuracy compared to Gaia is $5$ mas Image quality is stable over all Q1 images with a full width at half maximum (FWHM) of $0.\!^{\prime\prime}16$. The stacked images (combining four nominal and two short exposures) reach $I_\mathrm{E} = 25.6$ ($10σ$, measured as the variance of $1.\!^{\prime\prime}3$ diameter apertures). We also describe quality control metrics provided with each image, and an appendix provides a detailed description of the provided data products. The excellent quality of these images demonstrates the immense potential of Euclid VIS data for weak lensing. VIS data, covering most of the extragalactic sky, will provide a lasting high-resolution atlas of the Universe.

Figures (23)

• Figure 1: Layout of quadrants in the FPA. The detectors, each containing four quadrants, are arranged in a $6\times6$ array. The mean CCD spacing is 1.53 ± 0.03mm and 7.74 ± 0.06mm in the $x$- and $y$-directions, respectively.
• Figure 2: First elements in the VIS PF. Input calibration products are shown on the left and output flagmaps are on the right. 'BFE' refers to the brighter-fatter effect (\ref{['sc:BFE']}), and 'PRNU' is the pixel response non-uniformity (\ref{['sc:flat']}). We note that CTI correction is not activated in Q1 processing due to limited radiation damage at this stage of the mission, and therefore it is not shown.
• Figure 3: Pre-launch measurements of VIS nonlinearity based on ground testing for CCD 6-2. Each of the four lines corresponds to a separate quadrant. Top panel: Measured intensity as a function of duration. Bottom panel: Linear signal divided by measured signal.
• Figure 4: Section of a VIS image (left panel) and the part of the associated flagmap (right panel). Grey pixels in the flagmap are objects, and red ones are identified as CR.
• Figure 5: Effect of BFE correction on the difference of the surface brightness of the brightest pixel of stars in nominal versus short exposures as a function of VIS magnitude in an aperture of 13 pixels, or ;;1.3 diameter.