Key points are not available for this paper at this time.
We decompose Pantheon+ Type Ia supernovae (SN) in hemispheres on the sky finding angular variations up to 4 km/s/Mpc, corresponding to a statistical significance up to 1. 9, in the Hubble constant H₀ both in the SH0ES redshift range 0. 0233<z<0. 15 and in extended redshift ranges. The variations are driven largely by variations in absolute magnitude from SN in Cepheid hosts but are reinforced by SN in the Hubble flow. H₀ is larger in a hemisphere encompassing the CMB dipole direction. The variations we see exceed the errors on the recent SH0ES determination, H₀=73. 041. 04 km/s/Mpc, but are not large enough to explain early versus late Universe discrepancies in the Hubble constant. Nevertheless, the Cepheid-SN distance ladder is anisotropic at current precision. The anisotropy may be due to a breakdown in the cosmological principle, or mundanely due to a statistical fluctuation in a small sample of SN in Cepheid host galaxies.
Conville et al. (Mon,) studied this question.