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Using the Keck Cosmic Web Imager we obtain spectra of several globularclusters (GCs), ultra compact dwarfs (UCDs) and the inner halo starlight ofM87, at a similar projected galactocentric radius of $\sim$5 kpc. This enablesus, for the first time, to apply the same stellar population analysis to theGCs, UCDs and starlight consistently to derive ages, metallicities andalpha-element abundances in M87. We find evidence for a dual stellar populationin the M87 halo light, i.e an $\sim$80\% component by mass which is old andmetal-rich and a $\sim$20\% component which is old but metal-poor. Two red GCsshare similar stellar populations to the halo light suggesting they may haveformed contemporaneously with the dominant halo component. Three UCDs, and oneblue GC, have similar stellar populations, with younger mean ages, lowermetallicities and near solar alpha-element abundances. Combined with literaturedata, our findings are consistent with the scenario that UCDs are the remnantnucleus of a stripped galaxy. We further investigate the discrepancy in theliterature for M87's kinematics at large radii, favouring a declining velocitydispersion profile. This work has highlighted the need for more self-consistentstudies of galaxy halos.

Keck Cosmic Web Imager (KCWI) Spectra of Globular Clusters and Ultra Compact Dwarfs in the Halo of M87