Globulars, Ellipticals, (non) Baryons: Enlightenment Gleaned from Bayes' (Theorem)

(with apologies to Douglas Hofstadter)

Broadly speaking, I study the properties of globular clusters (GCs), elliptical galaxies, and dark matter (DM) halos. GCs, well-worth studying in their own right, can act as tracers of the dark matter content of galaxies, both directly as kinematic probes and indirectly through GC system mass-halo mass scaling relations. In addition, the spatial, color, and magnitude distributions of GCs about a galaxy offer the promise of distinguishing between different galaxy formation histories.

Despite GCs being readily observable in the local universe, large uncertainties in our models of GC formation hinder our ability to use GCs as tools for understanding galaxies and DM. However, successfully reproducing the observed distributions of GCs requires understanding all three entwined components of this braid (okay, enough half-baked GEB references). Hence, my work proceeds in gradual steps in different directions of the GC-galaxy-DM connections.

My work has mostly been in the regime of "small data" where model assumptions can have a large impact on any results. Thus I have maintained an interest in Bayesian statistics, where prior beliefs can be cleanly incorporated into the modeling process and the results of various assumptions readily quantified.

Some questions I am currently interested in:

• Do the red (metal-rich) and blue (metal-poor) GC subpopulations correspond to in-situ and ex-situ components respectively of the stellar mass of galaxies? Or are they more appropriate described as some mixture of the two?
• Are metal-poor globular clusters really galaxies? That is, did they form in very low mass DM halos at the very earliest epoch of star formation in the universe?
• What does the orbital anisotropy structure of GCs (and the outer stellar halo in general) tell us about the accretion history of galaxies?
• To what extent is the DM halo mass-GC system mass scaling relation due to mergers in a hierarchical universe versus due to some intrinsic connection between DM and GC formation?
• Is the information content in the kinematics of GC systems in massive elliptical galaxies sufficient to "break" the mass-anisotropy degeneracy in equilibrium dynamical models?