M33’s unresolved evolutionary and assembly history

Determine the evolutionary history and assembly pathway of the Triangulum Galaxy (M33), including the relative roles of mergers, accretion, and in-situ evolution.

Background

The paper motivates its study by noting that competing observational and dynamical results provide different pictures of M33’s interaction history. Earlier imaging suggested a possible past close encounter with M31, whereas more recent proper-motion and disk-modeling studies favor first infall and recent gas accretion. Evidence for an accreted stellar halo further indicates that M33’s formation history is not fully established.

The APOGEE integrated-light measurements of M33 star clusters are used to identify disk-like and halo-like populations and possible accreted clusters, but they do not uniquely determine the galaxy’s complete evolutionary history. The unresolved issue is therefore the overall assembly pathway of M33 and the contribution of accretion relative to in-situ formation.