Where stellar halos coexist with intracluster light

The work presented in this thesis studies the role that accretion
events play in the evolution of galaxies in dense environments,
such as galaxy clusters. Cosmological simulations allow us to study
in detail the evolution of galaxies' halos in cluster environments
and have shown that the formation of extended halos around central
cluster galaxies and intracluster light (ICL) is closely correlated
to the morphological transformation of galaxies in clusters.
However, the extremely low surface brightness of these components
makes it difficult to gather observational constraints. This thesis
studies the light and stellar motion in the halo of the giant
elliptical galaxy M87 and its surrounding IC component at the
centre of the Virgo cluster. Virgo is the nearest ($\sim 15$~Mpc
away) large scale structure, a young cluster characterised by both
spatial and kinematic substructures. M87 has one of the oldest
stellar populations in the local Universe and a stellar halo that
contains $\sim$ 70\% of the galaxy light down to $\rm{\mu_{V}=27\,
mag\, arcsec^{-2}}$. Moreover, deep images of the Virgo cluster
core have revealed an extended network of tidal features suggesting
that accretion events characterise its mass assembly. Thus, M87 and
its host environment are prime targets to shed light on the
hierarchical assembly of structure in the Universe. This work uses
new Suprime-Cam@Subaru photometry and FLAMES@VLT spectroscopy to
study a $\sim 0.5\, \rm{deg^2}$ area around M87, in the transition
region between galaxy halo and ICL. We use planetary nebulas (PNs)
as tracers, whose strong [OIII] $\lambda$5007 \AA\ emission line
makes them excellent photometric and kinematic probes, also at
large distances from the galaxy's centre. The photometric analysis
of the PN sample shows the superposition of two stellar
populations, both halo and ICL. This is confirmed by
spectroscopically detected PNs, whose velocity phase-space also
reveals that halo and ICL split into two different kinematic
components. They have very different spatial distributions and
parent stars, as indicated by the properties of the PN populations
they are associated with, such as the $\alpha$-parameter and the
slope of the planetary nebula luminosity function (PNLF). In this
thesis I give the observational proof that in Virgo the central
galaxy and the ICL both evolve through the ongoing accretion of
smaller systems. However, stellar halo and ICL are dynamically
distinct components with different velocity and density
distributions, and parent stellar populations. Whether or not these
conclusions are true for different galaxies in different Virgo
subclusters is still an open question and the topic of one of my
planned future studies.