Dynamical Constraints on the Local Group from the CMB and 2MRS Dipoles

TL;DR

This paper constrains the Local Group's dynamics by comparing CMB and galaxy sample dipoles, accounting for obscured regions and unknown velocities, revealing significant extra motion towards the Galactic center.

Contribution

It introduces a method to incorporate unobserved regions and unknown velocities in Local Group motion analysis, providing new constraints on its dynamics.

Findings

Detected significant extra motion towards the Galactic center

Quantified the impact of the Zone of Avoidance on velocity estimates

Suggested future surveys could better constrain the transverse velocity

Abstract

We place constraints on the dynamics of the Local Group (LG) by comparing the dipole of the Cosmic Microwave Background (CMB) with the peculiar velocity induced by the 2MRS galaxy sample. The analysis is limited by the lack of surveyed galaxies behind the Zone of Avoidance (ZoA). We therefore allow for a component of the LG velocity due to unknown mass concentrations behind the ZoA, as well as for an unknown transverse velocity of the Milky Way relative to the Andromeda galaxy. We infer extra motion along the direction of the Galactic center (where Galactic confusion and dust obscuration peaks) at the 95% significance level. With a future survey of the ZoA it might be possible to constrain the transverse velocity of the Milky Way relative to Andromeda.