Non-Gaussianity and CMB aberration and Doppler

TL;DR

This study investigates whether observer motion-induced aberration and Doppler effects bias non-Gaussianity measurements in CMB maps, finding that for Gaussian primordial maps, the bias is negligible compared to cosmic variance.

Contribution

The paper demonstrates through simulations that aberration and Doppler effects do not significantly bias $f_{NL}$ estimates in Gaussian CMB maps, simplifying analysis assumptions.

Findings

Bias from aberration/Doppler is less than half the cosmic variance for $f_{NL}$

Neglecting these effects is safe for Gaussian primordial maps

Effects on non-Gaussian maps require further study

Abstract

The peculiar motion of an observer with respect to the CMB rest frame induces a deflection in the arrival direction of the observed photons (also known as CMB aberration) and a Doppler shift in the measured photon frequencies. As a consequence, aberration and Doppler effects induce non trivial correlations between the harmonic coefficients of the observed CMB temperature maps. In this paper we investigate whether these correlations generate a bias on Non-Gaussianity estimators $f_{NL}$. We perform this analysis simulating a large number of temperature maps with Planck-like resolution (lmax $= 2000$) as different realizations of the same cosmological fiducial model (WMAP7yr). We then add to these maps aberration and Doppler effects employing a modified version of the HEALPix code. We finally evaluate a generalization of the Komatsu, Spergel and Wandelt Non-Gaussianity estimator for all the simulated maps, both when peculiar velocity effects have been considered and when these phenomena have been neglected. Using the value $v/c=1.23 \times 10^{-3}$ for our peculiar velocity, we found that the aberration/Doppler induced Non-Gaussian signal is at most of about half of the cosmic variance $\sigma$ for $f_{NL}$ both in a full-sky and in a cut-sky experimental configuration, for local, equilateral and orthogonal estimators. We conclude therefore that when estimating $f_{NL}$ it is safe to ignore aberration and Doppler effects {\it if} the primordial map is already Gaussian. More work is necessary however to assess whether a map which contains Non-Gaussianity can be significantly distorted by a peculiar velocity.