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The largest fluctuation in the CMB sky is the CMB dipole, which is believedto be caused by the motion of our observation frame with respect to the CMBrest frame. This motion accounts for the known motion of the Solar Systembarycentre with a best-fit amplitude of $369$ km/s, in the direction ($\ell=264^\circ$, $b=48^\circ$) in galactic coordinates. Along with the CMB dipolesignal, this motion also causes an inevitable signature of statisticalanisotropy in the higher multipoles due to the modulation and aberration of theCMB temperature and polarization fields. This leads to a correlation betweenadjacent CMB multipoles causing a non-zero value of the off-diagonal terms inthe covariance matrix which can be captured in terms of the dipolar spectra ofthe bipolar spherical harmonics (BipoSH). In our work, we jointly infer the CMBpower spectrum and the BipoSH spectrum in a Bayesian framework using the$\textit{Planck}$-2018 $\texttt{SMICA}$ temperature map. We detect amplitudeand direction of the local motion consistent with the canonical value $v=369$km/s inferred from CMB dipole with a statistical significance of $4.54\sigma$,$4.97\sigma$ and $5.23\sigma$ respectively from the masked temperature map withthe available sky fraction $40.1\%$, $59.1\%$, and $72.2\%$, confirming thecommon origin of both the signals. The Bayes factor in favor of the canonicalvalue is between $7$ to $8$ depending on the choice of mask. But it stronglydisagrees (by a value of the Bayes factor about $10^{-10}-10^{-11}$) with ahigher value of local motion which one can infer from the amplitude of thedipole signal obtained from the CatWISE2020 quasar catalog using the WISE andNEOWISE data set.

Bayesian estimation of our local motion from the Planck-2018 CMB temperature map