Cosmic variance of the local Hubble flow in large-scale cosmological simulations

Understand

The increasing precision in the determination of the Hubble parameter has reached a per cent level at which large-scale cosmic flows induced by inhomogeneities of the matter distribution become non-negligible.

• Here we use large-scale cosmological N-body simulations to study statistical properties of the local Hubble parameter as measured by local observers.
• We show that the distribution of the local Hubble parameter depends not only on the scale of inhomogeneities, but also on how one defines the positions of observers in the cosmic web and what reference frame is used.
• Observers located in random dark matter haloes measure on average lower expansion rates than those at random positions in space or in the centres of cosmic voids, and this effect is stronger from the halo rest frames compared to the CMB rest frame.