The Cluster and Large Scale Environments of Quasars at z<0.9

TL;DR

This thesis investigates quasar environments across redshifts, examining their relation to galaxy clusters, environment evolution, and orientation, revealing a preference for less dense regions and potential environmental differences at high redshift.

Contribution

It introduces new measurements of quasar orientations relative to galaxy clusters and explores environment evolution and spectral features across a large redshift range.

Findings

Quasars avoid cluster centers at 0.4<z<0.8, favoring less dense environments.

No significant change in quasar environment with redshift or luminosity.

High redshift quasars show ultra-strong UV FeII emission possibly linked to environment.

Abstract

In this thesis, I present an investigation into the environments of quasars with respect to galaxy clusters, and environment evolution with redshift and luminosity. The orientation of the quasar with respect to the major axis of the closest cluster was calculated, introducing new information to previous work. The aim of this work was i.) to study the large scale environment over a large redshift range, ii.) to study the evolution as well as any change in environment with quasar luminosity and redshift, and iii.) to study the orientation of a quasar with respect to a galaxy cluster. There is a deficit of quasars lying close to cluster centres for 0.4<z<0.8, indicating a preference for less dense environments, in agreement with previous work. These is no change with redshift (over 0<z<1.2) in the positions of the quasars as a function of absolute quasar magnitude, nor preferred orientation between the quasar and the cluster major axis for bright or faint quasars. Spectra of a selection of 680 star forming galaxies, red galaxies, and AGN were taken, and used to study the environments of quasars with respect to star-forming galaxies and galaxy clusters. The objects were classified (33 classed as AGN), and star formation rates calculated. Three AGN and 10 star forming galaxies lie at the same redshift (z=0.29) as three galaxy clusters. The three galaxy clusters have the same orientation angle and may be part of a filament along with the star forming galaxies and AGN. A number of high redshift quasars showed evidence of ultra-strong UV FeII emission in their spectra in the direction of three LQGs in the redshift range 1.1<z<1.6, including the Clowes-Campusano Large Quasar Group (CCLQG). Though there has been no previous indication that the LQG environment is unique, the high level of iron emission may indicate a difference in environment.