The tangential velocity of M31: CLUES from constrained simulations

TL;DR

This paper uses constrained simulations to estimate the tangential velocity of M31, reconciling conflicting measurements and assessing their compatibility with LambdaCDM cosmology.

Contribution

It introduces a Bayesian approach with constrained simulations to evaluate M31's tangential velocity and its consistency with LambdaCDM, considering environmental effects.

Findings

Constrained simulations favor higher tangential velocities for M31.

Unconstrained simulations tend to underestimate M31's tangential velocity.

Both estimates are compatible with LambdaCDM within uncertainties.

Abstract

Determining the precise value of the tangential component of the velocity of M31 is a non trivial astrophysical issue, that relies on complicated modeling. This has recently lead to con- flicting estimates, obtained by several groups that used different methodologies and assump- tions. This letter addresses the issue by computing a Bayesian posterior distribution function of this quantity, in order to measure the compatibility of those estimates with LambdaCDM. This is achieved using an ensemble of local group (LG) look-alikes collected from a set of Con- strained Simulations (CSs) of the local Universe, and a standard unconstrained LambdaCDM. The latter allows us to build a control sample of LG-like pairs and to single out the influence of the environment in our results. We find that neither estimate is at odds with LambdaCDM; how- ever, whereas CSs favour higher values of vtan , the reverse is true for estimates based on LG samples gathered from unconstrained simulations, overlooking the environmental element