Observing the peculiar acceleration of our Solar System with quasar proper motions

We measured the proper motion dipole of quasars observed by to determine the acceleration of the Solar System with respect to the quasar rest frame. This secular aberration drift provides a purely kinematic measurement of the Galactic acceleration of the Solar System and a mandatory correction for high-precision astrometric reference frames. We characterised the full angular power spectrum of the proper motion field using the pseudo-C_ scanning strategy, stellar density and stellar proper motion maps was used to diagnose the origin of systematic power beyond the dipole. We applied this framework to both the EDR3 quasar catalogue and the Quaia catalogue. The inferred acceleration is consistent with the previous determination, but the credible intervals widen by factors of 1.5 to 5 when higher-multipole degeneracies are properly marginalised, indicating that previous uncertainty estimates were optimistic. Our best estimate, based on the Quaia catalogue, is (g_x,,g_y,,g_z) = Gaia formalism and employed simulation-based inference to jointly constrain the dipole and higher multipole power. Cross-correlation with the Gaia Gaia +0.72 _ -0.72 , ,-4.94^ +0.54 _ -0.55 ,,-2.13^ +0.58 _ -0.58 ̊ight) ;̊m μ as ,yr^ -1 . This corresponds to an amplitude of 5.55_ -0.53 ^ +0.54 ,̊m ;μ as,yr^ -1 , where 𝐠 = 𝐚/c is the Solar System acceleration expressed as a proper motion drift in equatorial coordinates. The inferred acceleration is directed towards (l,, b) = łeft(11.71^ +7.0 _ -6.8 ,, -9.01^ +7.0 _ -6.9 ̊ight)^̧irc, equivalently (α,, δ) = łeft(281.39^ +7.8 _ -8.0 ,, -22.93^ +6.5 _ -6.2 ̊ight)^̧irc. This is in good agreement with a Galactic centre--dominated acceleration. The acceleration components show no significant dependence on source redshift, providing further evidence of the acceleration's kinematic origin