Constraining H0 Via Extragalactic Parallax

TL;DR

This paper explores the potential of measuring the Hubble constant $H_0$ through extragalactic secular parallax, using surveys of nearby galaxies and astrometric data, to address current $H_0$ measurement tensions.

Contribution

It presents a forecast method combining Fisher formalism and simulations to estimate $H_0$ precision from parallax measurements of galaxies, considering peculiar velocities.

Findings

Optimal survey includes about 100 galaxies within z=0.06

Proper motion errors needed are comparable to Gaia's capabilities

Parallax-based $H_0$ measurement can help resolve existing tensions

Abstract

We examine the prospects for measurement of the Hubble parameter $H_0$ 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 $H_0$ measurement. We use both a Fisher information formalism and simulations to forecast errors in $H_0$ from such surveys, marginalizing over the unknown peculiar velocities. The optimum survey observes $\sim 10^2$ galaxies within a redshift $z_\mathrm{max}=0.06$. The required errors on proper motion are comparable to those that can be achieved by Gaia and future astrometric instruments. A measurement of $H_0$ via parallax has the potential to shed light on the tension between different measurements of $H_0$.