To unveil the nature of 95% of the Universe, missions such as Euclid aim at reaching a few percent precision. In this quest for precision, tensions between the standard cosmological model and observations already arise: local and global H0 measurements are incompatible at more than 3-sigma, anomalies emerge within the CMB, small scale simulations mismatch detailed small scale observations. These tensions suggest that we should perhaps not be so quickly inclined to disregard our observational site as a bias factor: Accuracy is not Precision. Few percent precision and local-induced biases are of the same order of magnitude. A precise mapping and modeling of the local distribution of matter is essential to properly account for these systematics. Simulations constrained to resemble the local Universe constitute the tool of choice for such studies. I will briefly introduce such simulations, that I baptized CLONES (Constrained LOcal & Nesting Environment Simulations), as well as present a few results, in particular regarding the Virgo cluster of galaxies, that promise to tremendously impact our capacity to evade systematics that will matter in future analyses to reach accurate precision cosmology.
Towards accurate precision cosmology with CLONES’ help