2020A&A...638L...8P

Spherical collapse predicts that a single value of the turnaround density, meaning the average matter density within the scale on which a structure detaches from the Hubble flow, characterizes all cosmic structures at the same redshift. It was recently shown by Korkidis et al. that this feature persists in complex non-spherical galaxy clusters that have been identified in N-body simulations. Here we show that the low-redshift evolution of the turnaround density constrains the cosmological parameters and it can be used to derive a local constraint on Ω_Λ,0 alone, independent of Ω_m,0. The turnaround density thus offers a promising new method for exploiting upcoming large cosmological datasets.