We investigate the possible anisotropy of the universe using the most up-to-date type Ia supernovae, i.e. the Pantheon+ compilation. We fit the full Pantheon+ data with the dipole-modulated $\Lambda$CDM model, and find that it is well consistent with a null dipole. We further divide the full sample into several subsamples with different high-redshift cutoff $z_c$. It is shown that the dipole appears at $2\sigma$ confidence level only if $z_c\leq 0.1$, and in this redshift region the dipole is very stable, almost independent of the specific value of $z_c$. For $z_c=0.1$, the dipole amplitude is $D=1.0_{ -0.4}^{ +0.4}\times 10^{ -3}$, pointing towards $(l,b)=(334.5_{ \ -21.6^{ \circ}}^{ \circ +25.7^{ \circ}},16.0_{ \ -16.8^{ \circ}}^{ \circ +27.1^{ \circ}})$, which is about $65^{ \circ}$ away from the CMB dipole. This implies that the full Pantheon+ is consistent with a large-scale isotropic universe, but the low-redshift anisotropy couldn't be purely explained by the peculiar motion of the local universe.
Categories: astro-ph.CO