Color Dependence of Dipole in CatWISE2020 Data

TL;DR

This study investigates the dipole anisotropy in quasar counts using CatWISE2020 data across different color bins, revealing significant variations and potential contamination affecting the cosmological interpretation.

Contribution

It identifies color-dependent differences in dipole signals and highlights contamination issues, providing new insights into the anisotropy analysis in quasar distributions.

Findings

Dipole signal varies significantly across color bins.

Contamination affects the reliability of certain color bins.

Estimated local velocity from dipole differs from CMB measurements.

Abstract

The signal of dipole anisotropy in quasar number counts is studied using the CatWISE2020 catalog in various color bins. It is found that the dipole signal differs significantly in two color bins, namely, $1.1>W1-W2\ge 0.8$ and $1.4>W1-W2>1.1$. The color bin $1.4>W1-W2>1.1$ appears strongly contaminated, with possibly Galactic contributions and is unreliable for extracting the signal of cosmological dipole. The source of this contamination has not been identified and cannot be attributed to known emissions within the galaxy. Removing this contaminated color bin leads to a strong dipole signal with a direction significantly different from that obtained from full data. If we interpret this dipole as due to our local motion, the extracted velocity turns out to be $900\pm 113$ Kms$^{-1}$, which deviates from the CMB dipole velocity with approximately $4.7$ sigma significance.