The VIRGO PN population and the mass assembly in M87

Cosmological simulations allow us to study in detail the evolution of galaxy halos in cluster environments, but the extremely low surface brightness of such components makes it difficult to gather observational constraints. Planetary nebulas (PNs) offer a unique tool to investigate these environments owing to their strong [OIII] emission line. We study the light and kinematics of the Virgo cluster and its central galaxy, M87, prime targets to address the topic of galaxy formation and evolution in dense environments. We make use of a deep and extended PN sample (similar to 300 objects) that extends out to 150 kpc in radius from M87's centre. We show that at all distance the galaxy halo overlaps with the Virgo intracluster light (ICL). Halo and ICL are dynamically distinct components with different parent stellar populations, consistent with the halo of M87 being redder and more metal rich than the ICL. The synergy between PN kinematic information and deep V/B-band photometry made it possible to unravel an ongoing accretion process in the outskirt of M87. This accretion event represents a non-negligible perturbation of the halo light, showing that this galaxy is still growing by accretion of smaller systems.