Big, Bigger, Biggest: Cosmology from Galaxy Cluster Alignment

Abstract

Galaxies are observed to align with the Large Scale Structure. This alignment can be a potential probe for cosmological information. Recently Galaxy Clusters have also been observed to align with the Large Scale Structure. We have looked into Galaxy Cluster Alignment as a potential probe for cosmological information in comparison with Galaxy Alignment. Clusters have a bigger alignment amplitude, however galaxies are much more numerous. We investigated where this trade off lies in 2 survey setups. First, we have investigated them in SDSS. Here we use the redMaPPer dataset for clusters. We predict that in this survey they generally have a better signal to noise than galaxies. Second, we have forecasted a cluster sample for LSST. We find that the signal quickly washes out with redshift due to a relatively low number count and a decreasing alignment amplitude with redshift. Galaxies give a significantly better signal to noise for LSST because of this. However, we also studied the effects of Weak Lensing for clusters. We predict that clusters seem to be less affected by this. Because of this it could be easier to extract the alignment signal from clusters than from galaxies. We have forecasted the CMB lensing - Alignment correlation in LSST as an interesting application of cluster alignments. We find that galaxies have a signal to noise that is about 50 percent better, however we predict clusters to be 10 times less contaminated by Weak Lensing.