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An effective $\boldsymbolΛ$-Szekeres modelling of the local Universe with Cosmicflows-4

Marco Galoppo, Leonardo Giani, Morag Hills, Aurélien Valade

TL;DR

The paperAddressing potential biases from local inhomogeneities, the authors develop an effective relativistic description of the nearby Universe by patching together multistructured $\Lambda$-Szekeres regions calibrated to the Cosmicflows-4 HAMLET reconstructions. They compute the fully inhomogeneous quasilocal expansion field and its impact on distance measurements to low-redshift SNe, employing a coarse-grained, quasi-linear approach to the local density and velocity fields. Applying this framework to Pantheon+ data, they find that local structure can shift inferred $H_0$ upward by about $0.5\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$ and that the corrections follow coherent sky patterns, not random scatter, suggesting that local structure alone cannot resolve the $H_0$ tension. Overall, the work provides a fully relativistic, field-level treatment of the local cosmic web and its implications for precision cosmology, highlighting the need to seek solutions to the Hubble tension beyond local-structure effects.

Abstract

We develop an effective description of the local cosmic environment, namely, for redshift $z \lesssim 0.1$, to quantify the bias induced by local structure on cosmological observables. Our approach models the metric of the nearby Universe as a superposition of multi-structured $Λ$-Szekeres patches, calibrated against the HAMLET peculiar velocity and density field reconstructions of Cosmicflows-4. From this framework we compute the fully inhomogeneous and anisotropic quasilocal expansion field predicted by our model, and use it to assess the impact of local structure on estimates of $H_0$. For this purpose we analyse low-redshift Type Ia supernovae from the Pantheon+ catalogue. We find that accounting for the local structure increases the Hubble tension, yielding a shift in the best-fit value of the Hubble constant of order $ΔH_0 \approx 0.5\ \mathrm{km\,s^{-1}Mpc^{-1}}$.

An effective $\boldsymbolΛ$-Szekeres modelling of the local Universe with Cosmicflows-4

TL;DR

The paperAddressing potential biases from local inhomogeneities, the authors develop an effective relativistic description of the nearby Universe by patching together multistructured -Szekeres regions calibrated to the Cosmicflows-4 HAMLET reconstructions. They compute the fully inhomogeneous quasilocal expansion field and its impact on distance measurements to low-redshift SNe, employing a coarse-grained, quasi-linear approach to the local density and velocity fields. Applying this framework to Pantheon+ data, they find that local structure can shift inferred upward by about and that the corrections follow coherent sky patterns, not random scatter, suggesting that local structure alone cannot resolve the tension. Overall, the work provides a fully relativistic, field-level treatment of the local cosmic web and its implications for precision cosmology, highlighting the need to seek solutions to the Hubble tension beyond local-structure effects.

Abstract

We develop an effective description of the local cosmic environment, namely, for redshift , to quantify the bias induced by local structure on cosmological observables. Our approach models the metric of the nearby Universe as a superposition of multi-structured -Szekeres patches, calibrated against the HAMLET peculiar velocity and density field reconstructions of Cosmicflows-4. From this framework we compute the fully inhomogeneous and anisotropic quasilocal expansion field predicted by our model, and use it to assess the impact of local structure on estimates of . For this purpose we analyse low-redshift Type Ia supernovae from the Pantheon+ catalogue. We find that accounting for the local structure increases the Hubble tension, yielding a shift in the best-fit value of the Hubble constant of order .

Paper Structure

This paper contains 10 sections, 38 equations, 8 figures.

Table of Contents

  1. Introduction
  2. An effective model for the local Universe
  3. Fields reconstruction from the Cosmicflows-4 data
  4. Coarse-grained spatial geometry
  5. Effective Λ-Szekeres reconstruction
  6. Quasilocal expansion field of the cosmic neighbourhood
  7. Impact on cosmological inference
  8. Conclusions
  9. The quasilocal formalism for Λ-Szekeres models
  10. Code routine validation

Figures (8)

  • Figure 1: Ratio $H_q/H_0$ in the three fundamental planes. Top row: SGX–SGY (left panel), SGX–SGZ (right panel); bottom row: SGY–SGZ.
  • Figure 2: The spatial profile and magnitude of $\bar{\Omega}_{Kq}$ on the SGX-SGY plane
  • Figure 3: The Hubble diagram for the low-$z$ subsample of Pantheon+ supernovae in the range $0.023<z<0.15$ (blue), and a comparison between the linear best fit (green) and the distance corrections on individual objects predicted by our Szekeres effective model (orange).
  • Figure 4: Posterior distribution over the cosmographic parameters $H_0$ and $q_0$ for the SH0ES supernova sample, comparing the standard FLRW model (blue contours) with the results including peculiar velocity corrections (orange contours) and the $\Lambda$-Szekeres corrections averaged over realisations (green contours).
  • Figure 5: Sky map of the $\Lambda$-Szekeres distance corrections, $\bar{\Delta} d_L^{\Lambda\text{-Sk}}(z, \hat{\mathbf{n}})$, for the SNe Ia within the low-redshift Pantheon+ sample, with the size of the dots indicating their redshifts in the CMB frame.
  • ...and 3 more figures