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| Main Authors: | , , , |
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| Format: | Preprint |
| Published: |
2024
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| Subjects: | |
| Online Access: | https://arxiv.org/abs/2412.14607 |
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Table of Contents:
- The cosmological principle asserting the large-scale uniformity of the Universe is a testable assumption of the standard cosmological model. We explore the constraints on anisotropic expansion provided by measuring directional variation in the Hubble constant, $H_0$, derived from differential zeropoint measurements of the Tully-Fisher distance estimator. We fit various models for directional variation in $H_0$ using the Tully-Fisher dataset from the all-sky Cosmicflows-4 catalog. The best-fit dipole variation has an amplitude of 0.063 $\pm$ 0.016 mag in the direction ($\ell,b$) = (142 $\pm$ 30$^{\circ}$, 52 $\pm$ 10$^{\circ}$). If this were due to anisotropic expansion it would imply a 3% variation in $H_0$, corresponding to $ΔH_0$ = 2.10 $\pm$ 0.53 km/s/Mpc if $H_0$ = 70 km/s/Mpc, with a significance of 3.9$σ$. A model that includes this $H_0$ dipole is only weakly favored relative to a model with a constant $H_0$ and a bulk motion of the volume sampled by Cosmicflows-4 that is consistent with the standard $Λ$CDM cosmology. However, we show that with the expected Tully-Fisher data from the WALLABY and DESI surveys it should be possible to detect a 1% $H_0$ dipole anisotropy at 5.8$σ$ confidence and to distinguish it from the typical bulk flow predicted by $Λ$CDM over the volume of these surveys.