The low multipoles in the Pantheon+SH0ES data

TL;DR

This paper analyzes low multipoles in supernova data, revealing significant monopole, dipole, and quadrupole components, suggesting complex velocity structures beyond simple bulk flows.

Contribution

It provides a detailed study of low multipoles in Pantheon+SH0ES data, highlighting their significance and redshift dependence, which was not previously characterized.

Findings

Monopole, dipole, and quadrupole are detected with high significance.

Quadrupole amplitude increases with redshift.

Monopole is significant only at very low redshift.

Abstract

In previous work we have shown that the dipole in the low redshift supernovae of the Pantheon+SH0ES data does not agree with the one inferred from the velocity of the solar system as obtained from CMB data. We interpreted this as the presence of significant bulk velocities. In this paper we study the monopole, dipole and quadrupole in the Pantheon+SH0ES data. We find that in addition to the dipole also both, the monopole and the quadrupole are detected with high significance. They are of similar amplitudes as the bulk flow. While the monopole is only significant at very low redshift, the quadrupole even increases with redshift.