(Proposal ID) S11A-077 (PI) Arnaboldi, Magda (Proposal Title) Tracing kinematic sub-structures in the halo of the giant elliptical galaxy M87 (Abstract) The long-lasting substructures preserved in the outer halos of giant elliptical galaxies are the best records of merger and accretion events that took place in the densest regions of the universe. Little is known about them observationally; however, the motions and chemical compositions of the stars in these halos provide vital information, which any galaxy formation theory must account for. Using the large new planetary nebula (PN) sample from the Suprime-Cam M87 PN survey, we can now measure the line-of-sight velocity distributions at various radii in the outer halo of the prototypical elliptical galaxy M87 in the Virgo cluster. In total, we propose to measure some 1500 PN velocities in the halo of M87 and search for substructure in the velocity histograms and phase-space diagrams, to unveil the fossil record caused by past accretion events. Combining data from the FOCAS spectrograph on Subaru and Flames on VLT will construct a unique database and a milestone for understanding the formation history of giant elliptical galaxies in general and the mass assembly at the centers of galaxy clusters.