Toward a Measurement of the Transverse Peculiar Velocity of Galaxy Pairs

The transverse peculiar velocities caused by the mass distribution of large-scale structure provide a test of the theoretical matter power spectrum and the cosmological parameters that contribute to its shape. Typically, the matter density distribution of the nearby Universe is measured through redshift or line-of-sight peculiar velocity surveys. However, both methods require model-dependent distance measures to place the galaxies or to differentiate peculiar velocity from the Hubble expansion. In this paper, we use the correlated proper motions of galaxy pairs from the VLBA Extragalactic Proper Motion Catalog to place limits on the transverse peculiar velocity of galaxy pairs with comoving separations 200 Mpc) are consistent with pure Hubble expansion to within ~ 5.3 microas/yr (1 sigma). Finally, we predict that Gaia end-of-mission proper motions will be able to significantly detect the mass distribution of large-scale structure on length scales < 25 Mpc. This future detection will allow a test of the shape of the theoretical mass power spectrum without a reliance on precise distance measurements.