Speaker
Description
Inhomogeneous cosmological models, such as the $\Lambda$-Szekeres model, provide a fully general relativistic way of describing structures in the local Universe through exact solutions of Einstein's equations. They thus provide a natural test bed to gauge the impact of local structures on cosmological inferences. We present the results of two separate but related investigations in which we utilise the $\Lambda$-Szekeres models.
Firstly, we test the application of a covariant cosmographic framework for local structures with axially-symmetric $\Lambda$-Szekeres models. We derive the cosmographic luminosity-distance expansion to fourth order in redshift, and compare this to the exact results determined via general relativistic ray tracing. This provides important insights into the levels of approximation obtainable from cosmographic expansions, as well as their non-trivial variance across a given observer's sky.
In the second investigation, we effectively model our local Universe for redshift $z \lesssim 0.1$ through a superposition of multi-structure $\Lambda$-Szekeres patches, using the peculiar velocity and HAMLET density reconstructions of the Cosmicflows-4 observational dataset. We compute the fully inhomogeneous and anisotropic quasilocal expansion field within our model, and thus analyse variations in $H_0$ estimates induced by the presence of local structure. Using low-redshift Type Ia supernovae from the Pantheon+ catalogue, we ultimately determine a shift in the best-fit Hubble constant value of order $\Delta H_0 \approx 0.5\ \mathrm{km\,s^{-1}Mpc^{-1}}$ , which further increases the Hubble tension.
| Research Area | Cosmology: late universe |
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