Testing the isotropy of cosmic acceleration with Pantheon+ and SH0ES: A cosmographic analysis

Abstract

We use a recent Pantheon+SH0ES compilation of Type Ia Supernova distance measurements at low-redshift, i.e., $0.01\le z\le 0.10$, in order to investigate the directional dependency of the deceleration parameter ($q_0$) in different patches ($60^{\circ }$ size) across the sky, as a probe of the statistical isotropy of the Universe. We adopt a cosmographic approach to compute the cosmological distances, fixing $H_0$ and $M_B$ to reference values provided by the collaboration. By looking at 500 different patches randomly taken across the sky, we find a maximum $\sim 3\sigma$ CL anisotropy level for $q_0$, whose direction points orthogonally to the cosmic microwave background (CMB) dipole axis, i.e., $(R{A}^{\mathrm{SN}},DE{C}^{\mathrm{SN}})=(267^{\circ },6^{\circ })$ vs $(R{A}^{\mathrm{CMB}},DE{C}^{\mathrm{CMB}})=(167^{\circ },-7^{\circ })$. We assessed the statistical significance of those results, finding that such a signal is expected due to the limitations of the observational sample. These results support that there is no significant evidence for a departure from the cosmic isotropy assumption, one of the pillars of the standard cosmological model.

Matches published version in PRD

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• Special Issue on Modified Gravity Approaches to the Tensions of $\Lambda$CDM: Goals and Highlights
• Testing inhomogeneous cosmography in our cosmic neighborhood using CosmicFlows-4
• Analysis of Pantheon+ supernova data suggests evidence of sign-changing pressure of the cosmological fluid
• Rates of Strongly Lensed Tidal Disruption Events
• Cosmic Dipoles from Large-Scale Structure Surveys
• An effective $\mathbf{\Lambda }$-Szekeres modelling of the local Universe with Cosmicflows-4
• A Quantitative Framework for Testing the Hubble Tension in a Bianchi Type I Cosmological Background