Orateur
Description
The Cosmological Principle predicts that, on sufficiently large scales, cosmic expansion should appear statistically isotropic to all observers. Testing the limitations of this prediction in the local Universe is, therefore, a first step into properly considering the impacts of local large-scale anisotropies in data analysis and interpretation. In this work, we use the Cosmicflows-4 distance compilation to reconstruct spatial fluctuations in the local expansion rate (up to $z=0.1$), obtaining its low $\ell$ multipoles, with special focus on the dipole and quadrupole of the expansion. The analysis is done in a completely model-independent way, allowing for a direct test of statistical isotropy without assuming a fiducial cosmological model. While the multipole amplitudes remain broadly consistent with $\Lambda$CDM expectations, the dipole and quadrupole exhibit a persistent coherence in direction across different redshift shells, with a probability below 0.001% in standard cosmological realizations. In this talk I will discuss the details and consequences of such findings.