Are anomalous cosmic flows a challenge for LCDM?

The dipolar moment of the peculiar velocity field, named bulk flow, is a sensitive cosmological probe: in parallel with the estimation issued from density fluctuations, it can give an indication on the value of cosmological parameters. Recent observations, based independently on composite velocity survey or velocity reconstruction from redshift survey, showed the existence of an anomalously high bulk flow in apparent contradiction with the linear prediction in ΛCDM cosmology. Using numerical simulations, we interpret this observation of consistently large cosmic flows on large scales as a signature of a rare event. Supposing we live in such a configuration and building samples with bulk flow profiles in agreement with the observations, we show that the asymmetric distribution of matter of large scales is responsible for the observed high bulk flow. To confirm the possible origin inΛCDM cosmology of such a bulk flow profile and the agreement with linear theory description, we carefully study the time-dependence of the bulk flow and the distribution of matter.