New M87 GCs metallicities from Keck & MMT sp.

Using observations from the Mitchell spectrograph at McDonald, LRIS at Keck, and Hectospec on the MMT, we derive new metallicity gradients from ~2 to 140kpc. We use a novel hierarchical statistical framework to simultaneously separate the GC system into subpopulations while measuring the metallicity gradients of those subpopulations.

We create physically motivated spectral stacks of the GC subpopulations by leveraging the output of this statistical framework to perform the first application of abundance tagging in a massive early-type galaxy to better constrain the origins of the GC subpopulations and thus the assembly history of M87. We find a metal-poor, {alpha}-enhanced population of GCs in both the inner and outer halos unanticipated by current cosmological simulations of galaxy evolution.