Clusters, brightest cluster galaxies and galaxy alignments

Abstract

This thesis develops two main topics related to the study of the large-scale structure of the Universe. The first one is the intrinsic alignment of galaxies. These are correlations between the shapes and orientations of galaxies that arise mainly as a consequence of tidal forces across a large range of scales. I use the tidal alignment model to predict how the intrinsic alignment of Luminous Red Galaxies could in the future provide constraints on the Baryon Acoustic Oscillation scale, a standard ruler for measuring the expansion of the Universe. I also show that primordial signatures of inflation can translate into a non-Gaussian bias in the correlation of the intrinsic shapes of galaxies, which could be observed with future surveys.

The second main topic discussed in this thesis is clusters of galaxies. I use data from the Sloan Digital Sky Survey and a public catalog of galaxy clusters to estimate the alignment of galaxies around groups and clusters of galaxies. The novelty of this work is mainly in the method for estimating the alignment signal. In photometric surveys, the redshift uncertainty is large compared to the size of a cluster, making the distinction between galaxies in the cluster and in the background very challenging. In the method developed here, each galaxy is assigned a posterior probability distribution function of its redshift to separate the alignment component from the gravitational lensing of galaxies in the background.

Among the galaxies that make up a cluster, Brightest Cluster Galaxies stand out by their luminosity. I study the connection between these galaxies and other ellipticals to understand the physics of their formation. Finally, I re-develop the Adaptive Matched Filter method for finding clusters in spectroscopic and photometric surveys to include a new treatment of the distances to galaxies. Again, I model the distance to each galaxy using a redshift posterior and propose other modifications to the algorithm that will be of use to upcoming photometric surveys.