Planck 2013 results. XXVII. Doppler boosting of the CMB: Eppur si muove

TL;DR

This paper reports the first measurement of our velocity relative to the CMB rest frame using Planck data, confirming the expected Doppler boosting effects on temperature anisotropies with high significance.

Contribution

It presents the first detection of Doppler boosting effects on CMB fluctuations due to our motion, using Planck satellite data.

Findings

Measured velocity component: 384 km/s with uncertainties.

Confirmed the known dipole direction with high significance.

Detected modulation and aberration effects consistent with our motion.

Abstract

Our velocity relative to the rest frame of the cosmic microwave background (CMB) generates a dipole temperature anisotropy on the sky which has been well measured for more than 30 years, and has an accepted amplitude of v/c = 0.00123, or v = 369km/s. In addition to this signal generated by Doppler boosting of the CMB monopole, our motion also modulates and aberrates the CMB temperature fluctuations (as well as every other source of radiation at cosmological distances). This is an order 0.1% effect applied to fluctuations which are already one part in roughly one hundred thousand, so it is quite small. Nevertheless, it becomes detectable with the all-sky coverage, high angular resolution, and low noise levels of the Planck satellite. Here we report a first measurement of this velocity signature using the aberration and modulation effects on the CMB temperature anisotropies, finding a component in the known dipole direction, (l,b)=(264, 48) [deg], of 384km/s +- 78km/s (stat.) +- 115km/s (syst.). This is a significant confirmation of the expected velocity.