Consistency of Pantheon+ supernovae with a large-scale isotropic universe*

Abstract

Abstract We investigate the possible anisotropy of the universe using data on the most up-to-date type Ia supernovae, i.e., the Pantheon+ compilation. We fit the full Pantheon+ data with the dipole-modulated ΛCDM model and find that the data are well consistent with a null dipole. We further divide the full sample into several subsamples with different high-redshift cutoffs . It is shown that the dipole appears at the confidence level only if , and in this redshift region, the dipole is very stable, almost independent of the specific value of . For , the dipole amplitude is , pointing toward , which is approximately away from the CMB dipole. This implies that the full Pantheon+ sample is consistent with a large-scale isotropic universe, but the low-redshift anisotropy could not be purely explained by the peculiar motion of the local universe.