Constraining H0 via extragalactic parallax

Abstract

ABSTRACT We examine the prospects for measurement of the Hubble parameter H0 via observation of the secular parallax of other galaxies due to our own motion relative to the cosmic microwave background rest frame. Peculiar velocities make distance measurements to individual galaxies highly uncertain, but a survey sampling many galaxies can still yield a precise H0 measurement. We use both a Fisher information formalism and simulations to forecast errors in H0 from such surveys, marginalizing over the unknown peculiar velocities. The optimum survey observes ∼102 galaxies within a redshift zmax = 0.06. The required errors on proper motion are comparable to those that can be achieved by Gaia and future astrometric instruments. A measurement of H0 via parallax has the potential to shed light on the tension between different measurements of H0.