Galactic Amnesia: The Information Washout of the Milky Way Merger History
Lina Necib, Dylan Folsom, Elliot Y. Davies, Nathaniel Starkman, Andreas Thoyas

TL;DR
This paper develops a quantitative framework using information theory to determine how well a galaxy's merger history can be reconstructed from present-day stellar chemodynamics, revealing the limits imposed by dynamical processes.
Contribution
It introduces a novel information-theoretic approach to quantify the recoverability of galaxy merger histories from observable chemodynamical data.
Findings
Gravitational potential and total energy are the most informative tracers of merger history.
Radial velocity information decays within approximately 5 Gyr.
Chemical abundances retain low, flat information levels over time.
Abstract
The merger history of a galaxy leaves imprints on its present-day stellar chemodynamics, yet dynamical processes progressively erase this record. We ask: how far back in time, and from which observables, can a galaxy's assembly history still be recovered? We provide a quantitative framework to address this question, using Mutual Information normalized by Shannon entropy to measure how much present-day stellar chemodynamics retains about each past merger's stellar mass and infall time . This framework is applied to TNG50 Milky Way -- like galaxies, with comparison to FIRE-2. We find that the gravitational potential and total energy are the most informative and longest-lived tracers of merger properties, highlighting the need for accurately measuring the Milky Way's potential. The information carried by the radial velocity decays to the noise floor within 5…
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