Barycenter kinematics in Local Group analogues

TL;DR

This paper introduces a novel method for identifying Local Group analogues in cosmological simulations by incorporating barycenter velocity constraints, revealing significant differences from traditional selection methods.

Contribution

The study demonstrates that including barycenter velocity constraints yields more accurate Local Group analogues, highlighting the importance of barycenter kinematics in simulation-based galaxy system identification.

Findings

Simulated galaxy pairs show less radial and more tangential M31 velocities when barycenter velocity is considered.

The radial change pattern is consistent across all tested cosmological models.

Matching observed barycenter velocity significantly impacts modeling of Local Group-like systems.

Abstract

We present a new way to identify systems similar to our Local Group (LG) of galaxies in cosmological simulations. Our method uses as a new constraint the speed and direction of the LG's center of mass, which we can measure accurately from cosmic microwave background data. When we apply these criteria to different cosmological simulations and compare the results with traditional selection methods, we find statistically significant differences. Our approach produces simulated galaxy pairs where the relative M31 velocity is less radial (2 percent to 7 percent difference over the mean) and more tangential (1 percent to 3 percent difference over the mean) than in cases that do not take into account the barycenter speed. The radial change pattern appears consistently across all cosmological models we test, showing that matching the observed barycenter velocity has a measurable effect when modeling and interpreting Local Group-like systems.