The Fate of Globular Cluster Substructure: A Kinematic Response to Galaxy Assembly
Finn A. Pal, Sarah L. Martell, Elizabeth J. Iles
TLDR
Globular clusters largely lose memory of their progenitor galaxies over cosmic time, limiting their use in reconstructing galaxy assembly histories.
Key contributions
- In-situ and ex-situ GCs show substantial kinematic overlap at z=0, making them hard to separate.
- Most memory of an accreted GC's progenitor is erased by the present day due to stochastic evolution.
- Few correlations persist, linking progenitor halo mass to GC population mass and number.
- Galactocentric distance of GC substructure correlates with progenitor maximum circular velocity.
Why it matters
This paper quantifies the limits of using present-day globular cluster kinematics to reconstruct galaxy merger histories. It shows that while GCs are useful tracers, their memory of progenitors is largely lost, challenging current assumptions.
Original Abstract
Globular clusters (GCs) are powerful tracers of galaxy assembly, frequently used to identify accreted substructure and reconstruct hierarchical merger histories. With advances in GC formation models and cosmological simulations, we can now better quantify the information about galaxy evolution encoded in present-day GCs. Here, we investigate how GC kinematics evolve over cosmic time and assess the extent to which GCs retain memory of the past of their host galaxy. Using a GC formation model applied to five Milky Way (MW) analogues from the Latte suite of the FIRE-2 simulations, we track the evolution of kinematic properties. At $z=0$, in-situ and ex-situ GCs exhibit substantial overlap in kinematic space, indicating that these populations are not clearly separable. We find that a subset of kinematic properties evolve in an ordered fashion across both in-situ and ex-situ populations, whereas others are dominated by stochastic variations. As a result, by the present day, most memory of the progenitor of an accreted GC is erased and only a few correlations persist. These correlations link progenitor halo mass to the total mass and number of a GC population, and the galactocentric distance of GC substructure to progenitor maximum circular velocity. These results highlight how both deterministic and stochastic processes driven by galaxy evolution shape GC kinematics and demonstrate the limits of reconstructing the assembly history of a galaxy from present-day GC orbits alone.
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