Galaxy clusters as intrinsic alignment tracers: present and future
  Galaxies and clusters embedded in the large-scale structure of the Universe
are observed to align in preferential directions. Galaxy alignment has been
established as a potential probe for cosmological information, but the
application of cluster alignments for these purposes remains unexplored.
Clusters are observed to have a higher alignment amplitude than galaxies, but
because galaxies are much more numerous, the trade-off in detectability between
the two signals remains unclear. We present forecasts comparing cluster and
galaxy alignments for two extragalactic survey set-ups: a currently-available
low redshift survey (SDSS) and an upcoming higher redshift survey (LSST). For
SDSS, we rely on the publicly available redMaPPer catalogue to describe the
cluster sample. For LSST, we perform estimations of the expected number counts
while we extrapolate the alignment measurements from SDSS. Clusters in SDSS
have typically higher alignment signal-to-noise than galaxies. For LSST, the
cluster alignment signals quickly wash out with redshift due to a relatively
low number count and a decreasing alignment amplitude. Nevertheless, a
potential strong-suit of clusters is in their interplay with weak lensing:
intrinsic alignments can be more easily isolated for clusters than for
galaxies. The signal-to-noise of cluster alignment can in general be improved
by isolating close pairs along the line of sight.
