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

We use a recent Pantheon+SH0ES compilation of type Ia supernova distance measurements at low-redshift, i.e., 0.01≤z≤0.10, in order to investigate the directional dependency of the deceleration parameter (q₀) in different patches (60^∘{} 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 H₀ and MB to reference values provided by the collaboration. By looking at 500 different patches randomly taken across the sky, we find a maximum ~3σ CL anisotropy level for q₀, whose direction points orthogonally to the cosmic microwave background (CMB) dipole axis, i.e., (RASN,DECSN)=(267^∘,6^∘) vs (RACMB,DECCMB)=(167^∘,-7^∘). 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.