First constraints on the intrinsic CMB dipole and our velocity with Doppler and aberration

TL;DR

This paper uses Planck 2018 data to independently measure the Doppler and aberration effects on the CMB, constraining the intrinsic dipole and the solar system's velocity without assuming the dipole is solely due to our motion.

Contribution

It provides the first independent measurements of Doppler and aberration effects to constrain the intrinsic CMB dipole and solar system velocity.

Findings

Upper limit on intrinsic CMB dipole: 3.7 mK (95% CI)

Solar system velocity estimate: ~300 km/s

Results consistent with the velocity hypothesis of the dipole

Abstract

We test the usual hypothesis that the Cosmic Microwave Background (CMB) dipole, its largest anisotropy, is due to our peculiar velocity with respect to the Hubble flow by measuring independently the Doppler and aberration effects on the CMB using Planck 2018 data. We remove the spurious contributions from the conversion of intensity into temperature and arrive at measurements which are independent from the CMB dipole itself for both temperature and polarization maps and both SMICA and NILC component-separation methods. Combining these new measurements with the dipole one we get the first constraints on the intrinsic CMB dipole. Assuming a standard dipolar lensing contribution we can put an upper limit on the intrinsic amplitude: 3.7 mK (95% CI). We estimate the peculiar velocity of the solar system without assuming a negligible intrinsic dipole contribution: $v = (300^{+111}_{-93})$ km/s with $(l,b) = (276 \pm 33, 51 \pm 19)^\circ$ [SMICA], and $v = (296^{+111}_{-88})$ km/s with $(l,b) = (280 \pm 33, 50 \pm 20)^\circ$ [NILC] with negligible systematic contributions. These values are consistent with the peculiar velocity hypothesis of the dipole.