The sparkling Universe: the coherent motions of cosmic voids

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We compute the bulk motions of cosmic voids, using a $\Lambda$CDM numerical simulation considering the mean velocities of the dark matter inside the void itself and that of the haloes in the surrounding shell.

• We find coincident values of these two measures in the range $\sim$ 300-400 km/s, not far from the expected mean peculiar velocities of groups and galaxy clusters.
• When analysing the distribution of the pairwise relative velocities of voids, we find a remarkable bimodal behaviour consistent with an excess of both systematically approaching and receding voids.
• We determine that the origin of this bimodality resides in the void large scale environment, since once voids are classified into void-in-void (R-type) or void-in-cloud (S-type), R-types are found mutually receding away, while S-types approach each other.