The complex case of MACSJ0717.5+3745 and its extended filament:
  intra-cluster light, galaxy luminosity function, and galaxy orientations
  The properties of galaxies are known to be affected by their environment, but
although galaxies in clusters and groups have been quite thoroughly
investigated, little is known presently on galaxies belonging to filaments of
the cosmic web, and on the properties of the filaments themselves. We
investigate here the properties of the rich cluster MACSJ0717.5+3745 and its
extended filament, by analyzing the distribution and fractions of intra-cluster
light (ICL) in the core of this cluster and by trying to detect intra-filament
light (IFL) in the filament. We analyze the galaxy luminosity function (GLF) of
the cluster core and of the filament. We also study the orientations of
galaxies in the filament to better constrain the filament properties. This work
is based on Hubble Space Telescope archive data, both from the Hubble Frontier
Fields in the F435W, F606W, F814W, and F105W bands, and from a mosaic of images
in the F606W and F814W bands. The spatial distribution of the ICL is determined
with our new wavelet-based software, DAWIS. The GLFs are extracted in the F606W
and F814W bands, with a statistical subtraction of the background, and fit with
Schechter functions. The galaxy orientations in the filaments are estimated
with SExtractor after correction for the Point Spread Function. We detect a
large amount of ICL in the cluster core, but no IFL in the cosmic filament. The
fraction of ICL in the core peaks in the F606W filter before decreasing with
wavelength. Though quite noisy, the GLFs in the filament are notably different
from those of field galaxies, with a flatter faint end slope and an excess of
bright galaxies. We do not detect a significant alignment of the galaxies in
the filament region that was analyzed.
