Publication at Faculty of Mathematics and Physics |

2023

The Lambda cold dark matter (Lambda CDM) standard cosmological model is in severe tension with several cosmological observations. Foremost is the Hubble tension, which exceeds 5 sigma confidence.

Galaxy number counts show the Keenan-Barger-Cowie (KBC) supervoid, a significant underdensity out to 300 Mpc that cannot be reconciled with Lambda CDM cosmology. Haslbauer et al. previously showed that a high local Hubble constant arises naturally due to gravitationally driven outflows from the observed KBC supervoid.

The main prediction of this model is that peculiar velocities are typically much larger than expected in the Lambda CDM framework. This agrees with the recent discovery by Watkins et al. that galaxies in the CosmicFlows-4 catalogue have significantly faster bulk flows than expected in the Lambda CDM model on scales of 100 - 250 h(-1) Mpc.

The rising bulk flow curve is unexpected in standard cosmology, causing 4.8 sigma tension at 200 h(-1) Mpc. In this work, we determine what the semi-analytic void model of Haslbauer et al. predicts for the bulk flows on these scales.

We find qualitative agreement with the observations, especially if our vantage point is chosen to match the observed bulk flow on a scale of 50 h(-1) Mpc. This represents a highly non-trivial success of a previously published model that was not constrained by bulk flow measurements, but which was shown to solve the Hubble tension and explain the KBC void consistently with the peculiar velocity of the Local Group.

Our results suggest that several cosmological tensions can be simultaneously resolved if structure grows more efficiently than in the Lambda CDM paradigm on scales of tens to hundreds of Mpc.