S 8 from peculiar velocities: agreement with Planck for Tully–Fisher and supernovae, tension for the fundamental plane

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ID: 319546
2026
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Abstract
Abstract Peculiar velocity measurements constrain the parameter combination fσ8, the product of the linear growth rate f and the fluctuation amplitude σ8. Under the approximation that f is a monotonic function of Ωm, this can be related to $S_8 \equiv \sigma _8 \sqrt{\Omega _{\rm m}/0.3}$, enabling direct comparison with weak lensing and cosmic microwave background results. We use three classes of direct-distance tracers—the Tully–Fisher relation, the fundamental plane, and Type Ia supernovae—to infer peculiar velocities. A unified hierarchical forward model jointly calibrates each distance indicator and a linear theory reconstruction of the local Universe. This is the first consistent Bayesian analysis to treat all three major classes of distance indicators within a common framework, enabling cross-checks of systematics across diverse galaxy populations. Combining the Tully–Fisher and Type Ia supernova samples, we obtain S8 = 0.798 ± 0.035 (fσ8 = 0.412 ± 0.018), in agreement with Planck and robust under the choice of galaxy bias model, with the uncertainty dominated by the variance of the 2M++ galaxy field. The fundamental plane constraints are instead unstable under the inhomogeneous Malmquist bias treatment; the quadratic extension preferred by the fundamental plane data drives their S8 values lower. These findings indicate that low-redshift peculiar velocity data are concordant with the cosmic microwave background and do not reinforce the early-versus-late S8 tension, though the fundamental plane results call for further scrutiny of their systematics.
Reference Key
openalex_W7167227218 Use this key to autocite in the manuscript while using SciMatic Manuscript Manager or Thesis Manager
Authors Richard Stiskalek
Journal monthly notices of the royal astronomical society
Year 2026
DOI
10.1093/mnras/stag1266
URL
https://doi.org/10.1093/mnras/stag1266
Keywords Keywords not found

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