The DES project

The Dark Energy Survey started in 2013 and is the largest photometric galaxy survey ever, having, in six years, imaged 5000 sq. deg. (a full octant of the sky) in five optical and near-infrared bands (grizY) to unprecedented depth (iAB ~ 24), and measuring the position on the sky, distance and shape of more than 200 million galaxies up to redshift z ~ 1.4. IFAE is a founding member of the collaboration, and designed and produced a large fraction of the readout electronics of the DES camera, DECam. The survey has as its main goal to unveil the nature of the mysterious dark-energy component of the universe that powers its current accelerated expansion.

During 2025, the main scientific effort of the group within the Dark Energy Survey (DES) focused on the completion and publication of the cosmological analyses of the full six-year dataset (DES Y6). These results (https://arxiv.org/abs/2601.14559) represent the culmination of more than a decade of observational and methodological development within the collaboration, delivering the most precise cosmological constraints obtained from DES to date. Members of the IFAE group played leading roles across several key components of the analysis pipeline, including photometric redshift calibration, weak-lensing magnification modelling, and cosmic shear cosmology.

These contributions constitute key ingredients of the final cosmological analyses. A clustering-redshift analysis led by PhD student William d’Assignies (https://arxiv.org/abs/2510.23565) significantly improved the validation and calibration of photometric redshift distributions, one of the dominant systematic uncertainties in large-scale structure and weak-lensing studies. He also played a leading role in implementing redshift uncertainties at the cosmological likelihood level (https://arxiv.org/abs/2506.00758), a key development for ensuring the robustness and accuracy of weak-lensing analyses. In parallel, PhD student Elisa Legnani led advances in the characterization and modelling of weak-lensing magnification (https://arxiv.org/abs/2601.14833), establishing methodologies to consistently incorporate magnification into multi-probe cosmological analyses. Complementing these efforts, postdoctoral researcher Simon Samuroff played a leading role in the DES-Y6 cosmic shear analysis (https://arxiv.org/abs/2602.10065), focusing on robust theoretical modeling and shear validation that are essential for achieving the required accuracy for cosmic shear, which remains the flagship weak lensing probe for DES.

Together, these activities highlight the sustained leadership of the IFAE DES group in the development of precision large-scale structure and weak-lensing analyses. The DES Y6 results mark a final milestone for the collaboration and provide a direct bridge toward upcoming cosmological analyses with next-generation surveys such as the Rubin Observatory LSST and the Euclid, in which IFAE is also actively participating.