Periodic Reporting for period 1 - UNICALS (UNIfied Cosmology Across Lensing Surveys)
Reporting period: 2023-09-01 to 2025-08-31
According to the current consensus cosmological model, dark matter and dark energy make up most of the energy density of the universe. However, their physical nature is still unknown and understanding them presents a grand challenge. Moreover, there are unresolved tensions between observations from the late-time and the early-time universe. Intriguingly, most weak lensing analyses favour a smoother matter distribution than Planck's Cosmic Microwave Background observations. In order to assess if this discrepancy is due to unaccounted systematics or new physics, it is essential to analyse the existing weak lensing datasets with a unified pipeline. This effort is especially required as we approach the next generation of dark energy surveys —including ESA's Euclid mission, the Vera C. Rubin Observatory Legacy Survey of Space and Time, and the Nancy Grace Roman Space Telescope— since they will provide unprecedented high-quality data that will increase the statistical power by orders of magnitude.
In this project, we aimed to combine for the first time the final data sets from the current generation of dark energy surveys (DES, KiDS and HSC) to obtain competitive cosmological constraints from the joint analysis of galaxy clustering and weak lensing. For this purpose, we have worked on developing a novel unified modelling and inference pipeline to fully exploit the statistical power of the different surveys in an optimal way. The methodology developed and employed in this project will be crucial to shed light on the existing tensions with Planck and the nature of dark energy with ESA's Euclid mission, the Rubin Observatory and the other upcoming dark energy surveys.
In this project, we aimed to combine for the first time the final data sets from the current generation of dark energy surveys (DES, KiDS and HSC) to obtain competitive cosmological constraints from the joint analysis of galaxy clustering and weak lensing. For this purpose, we have worked on developing a novel unified modelling and inference pipeline to fully exploit the statistical power of the different surveys in an optimal way. The methodology developed and employed in this project will be crucial to shed light on the existing tensions with Planck and the nature of dark energy with ESA's Euclid mission, the Rubin Observatory and the other upcoming dark energy surveys.
An optimized lens sample has been selected from the DES final dataset. At the same time, source samples have been selected from the DES and KiDS final datasets, respectively. Using the lens and source samples from the DES final dataset, we have obtained measurements of galaxy clustering and galaxy-galaxy lensing. We have also obtained weights that will be applied to these measurements in order to correct for observational systematics. We have estimated these weights with two independent methods, already used for the DES Year 3 analysis: Iterative Systematics Decontamination (ISD) and Elastic Net (ENet), which is a machine learning method.
Regarding the redshift distributions, we have estimated redshift distributions for the DES lens and source samples, as well as for the KiDS source sample. We have also obtained measurements of cosmic shear for the final datasets of DES and KiDS. In addition, we have estimated a covariance for the DES final dataset combining weak lensing and galaxy clustering. We also dispose of covariances for KiDS Legacy (final dataset) and HSC year-3 cosmic shear. Last, we have a functioning unified modelling pipeline and a fiducial set of priors that we can use for our combined analysis of multiple surveys.
Regarding the redshift distributions, we have estimated redshift distributions for the DES lens and source samples, as well as for the KiDS source sample. We have also obtained measurements of cosmic shear for the final datasets of DES and KiDS. In addition, we have estimated a covariance for the DES final dataset combining weak lensing and galaxy clustering. We also dispose of covariances for KiDS Legacy (final dataset) and HSC year-3 cosmic shear. Last, we have a functioning unified modelling pipeline and a fiducial set of priors that we can use for our combined analysis of multiple surveys.
The main result of this project is the selection and calibration of the galaxy samples for the DES and KiDS final datasets. These are some of the key ingredients for the DES and KiDS weak lensing cosmological analyses. Dozens of scientific publications will use these data products in the future, and they will be state of the art until the community gets access to new data from the Euclid mission, which will happen in a few years. The main objective of this project has not been achieved yet due to the early termination of the grant. However, we plan to continue pursuing our original goals in the coming months.