2025MNRAS.543.1556S

Several observational studies suggest that the local few hundred Mpc around the Local Group is significantly underdense based on source number counts in redshift space across much of the electromagnetic spectrum, particularly in near-infrared galaxy counts. This 'Keenan-Barger-Cowie (KBC) void', 'Local Hole', or 'local supervoid' would have significant ramifications for the Hubble tension by generating outflows that masquerade as an enhanced local expansion rate. We evaluate models for the KBC void capable of resolving the Hubble tension with a background Planck cosmology. We fit these models to direct distances from the Tully-Fisher catalogue of the CosmicFlows-4 compilation using a field-level forward model. Depending on the adopted void density profile, we find the derived velocity fields prefer a void size $\lesssim 70$ Mpc, which is $\lesssim 10$ per cent of the fiducial size found by Haslbauer et al. based on the KBC luminosity density data. The predicted local Hubble constant is $72.1^{+0.9}_{-0.8}$, $70.4^{+0.4}_{-0.4}$, or $70.2^{+0.5}_{-0.4}$ km s^–1 Mpc^–1 for an initial underdensity profile that is exponential, Gaussian, or Maxwell-Boltzmann, respectively. The latter two ameliorate the Hubble tension to within $3\sigma$ of the four-anchor distance ladder approach of Breuval et al., which gives $73.2 \pm 0.9$ km s^–1 Mpc^–1. The exponential profile achieves consistency with this measurement at just over $1\sigma$, but it is disfavoured by the Bayesian evidence. The preferred models produce bulk flow curves that disagree with recent estimates from CosmicFlows-4, despite the void models being flexible enough to match such estimates.