Investigating galaxies in and behind Galaxy Clusters using Strong Gravitational Lensing

Gravitational Lensing is a unique technique to investigate the dark
matter distribution of structures in the Universe, from galaxies,
through galaxy groups, clusters, up to the large-scale structure.
It allows us to map the total projected mass density of structures
acting as lenses, and thus to shed light on the distribution and
properties of the otherwise-invisible dark matter. Clusters of
galaxies are the largest virialized structures in the universe.
Gravitational lensing analysis allows us to study their mass
distribution in great detail. Weak lensing probes the mass
distribution in the outskirts of clusters based on a statistical
analysis of the shape distortion observed in hundreds of galaxies
behind the cluster. Strong lensing, instead, allows us to
reconstruct high resolution mass and magnification maps of the
central region of the cluster. In addition, thanks to the lensing
magnification of background sources, galaxy clusters act as
"Gravitational Telescopes" and can be used to investigate the
galaxy population of the early Universe at z>5. In the first
part of my Thesis I use the CLASH and Frontier Fields cluster RXC
J2248 to investigate sources at z~6. At such and higher redshift
galaxies appear as optical dropouts, since the light they emit is
redshifted to NIR wavelengths and no flux is observed in the UV and
optical filters. I discovered a z~6 lensed galaxy in the core of
RXC J2248 which appears as a quintuple lensed optical dropout in
the 16 HST filters of the CLASH survey. I perform a detailed
photometric analysis of these dropouts to verify that they present
the same photometric properties and are actually multiple images of
the same source. In addition, by performing the strong lensing
analysis of the cluster core I verify that the lensing model
supports the quintuple and z~6 nature of this system. In the second
part of my Thesis I use strong gravitational analysis of the CLASH
cluster A383 to probe the details of the mass distribution of
galaxies in the cluster core. Well known luminosity scaling
relations allow us to relate the physical properties as stellar
velocity dispersion and size of the elliptical galaxies to their
observed luminosity. However in clusters, galaxies suffer tidal
stripping due to the interaction with other cluster members and the
cluster dark matter halo. The goal of this work is to measure the
galaxy halo sizes in a cluster core to quantify how much mass was
stripped relative to field galaxies. Here I present a new approach
to strong lensing analysis of clusters, in which I use measurements
of cluster members' velocity dispersions as additional constraints
in the lens modeling. I apply this analysis to Abell 383 to
separate the galaxy mass content from the smooth dark matter mass
component and investigate how the dark matter halo size scales with
the galaxy luminosity in the cluster core. In addition I perform
the surface brightness reconstruction of the southern giant arcs to
improve constraints on close by individual galaxies and study
possible deviations from the global scaling law measured for the
cluster.