The effects of lensing by local structures on the dipole of radio source counts

Abstract

ABSTRACT Our peculiar motion in a homogeneous and isotropic universe imprints a dipole in the cosmic microwave background (CMB) temperature field and similarly imprints a dipole in the distribution of extragalactic radio sources on the sky. Each of these effects have been measured; however, each of these measurements give different results for the velocity of our motion through the Universe: the radio dipole measurements finds the speed of our motion to be around three times larger than that of the CMB. Here we show the effects of the previously unconstrained lensing dipole, whereby necessarily local structures (required for large angular lensing scales) will distort the distribution of radio sources on the sky. We find that the inclusion of these effects does not reduce the tension between the CMB and radio source dipole measurements; however, without their inclusion future extragalactic number counts could lead to incorrect inferences of our peculiar motion. In addition we can constrain the size of the lensing dipole to be κ < 3 · 10−2 at the 2σ level.