Testing the local supervoid solution to the Hubble tension with direct distance tracers

TL;DR

This study evaluates whether a local supervoid can resolve the Hubble tension by fitting models to direct distance data, finding smaller void sizes than previously suggested and partial agreement with local Hubble constant measurements.

Contribution

It provides a detailed analysis of local supervoid models using direct distance tracers, constraining their size and impact on the Hubble tension with novel field-level modeling.

Findings

Void size less than 70 Mpc, smaller than previous estimates.

Predicted local Hubble constant around 70 km/s/Mpc, reducing tension.

Models with Gaussian or Maxwell-Boltzmann profiles better match local Hubble measurements.

Abstract

Several observational studies suggest that the local few hundred Mpc around the Local Group are 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 to prefer a void size of less than 70 Mpc, which is less than 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/Mpc 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 4-anchor distance ladder approach of Breuval et al. giving $73.2 \pm 0.9$ km/s/Mpc. The exponential profile does achieve 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.