Bayesian estimation of our local motion from the Planck-2018 CMB
  temperature map
  The largest fluctuation in the CMB sky is the CMB dipole, which is believed
to be caused by the motion of our observation frame with respect to the CMB
rest frame. This motion accounts for the known motion of the Solar System
barycentre 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 dipole
signal, this motion also causes an inevitable signature of statistical
anisotropy in the higher multipoles due to the modulation and aberration of the
CMB temperature and polarization fields. This leads to a correlation between
adjacent CMB multipoles causing a non-zero value of the off-diagonal terms in
the covariance matrix which can be captured in terms of the dipolar spectra of
the bipolar spherical harmonics (BipoSH). In our work, we jointly infer the CMB
power spectrum and the BipoSH spectrum in a Bayesian framework using the
$\textit{Planck}$-2018 $\texttt{SMICA}$ temperature map. We detect amplitude
and 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 with
the available sky fraction $40.1\%$, $59.1\%$, and $72.2\%$, confirming the
common origin of both the signals. The Bayes factor in favor of the canonical
value is between $7$ to $8$ depending on the choice of mask. But it strongly
disagrees (by a value of the Bayes factor about $10^{-10}-10^{-11}$) with a
higher value of local motion which one can infer from the amplitude of the
dipole signal obtained from the CatWISE2020 quasar catalog using the WISE and
NEOWISE data set.
