Exploring scaling relations and catalogue completeness using the XMM Cluster Survey

We are entering an era of precision cosmology, using tens of thousands of clusters to place robust constraints on cosmological parameters.  However, to do this, we must understand systematic effects in the analysis. In this thesis, we aim to understand the effects of selection from multi-wavelength observations and the resulting scaling relations from the samples constructed. I present two distinct pieces of analysis:

In the first, I create two samples of galaxy clusters drawn from four X-ray contiguous regions comprising a total area of 57.4 deg2 - one optically selected from the analysis of three years of Dark Energy Survey (DESY3) observations using the redMaPPer cluster detection algorithm and another X-ray selected from XMM observations comprising the XMM Cluster Survey (XCS). I consider the completeness of both the redMaPPer and XCS selected cluster samples and find that redMaPPer recovers all XCS extended sources within a defined parameter space. For each sample, I extract X-ray luminosity and temperature data from the XCS survey and richness data from the redMaPPer catalogue and investigate the form of the X-ray luminosity-temperature (LX − TX ), luminosity-richness (LX − λ) and temperature-richness (TX −λ) scaling relations. We find that the form of the LX −TX relation is consistent between the two selection methods used. However, we find tentative evidence for a steepening of the slope of the relation for low richness systems in the X-ray selected sample. When considering the scaling of richness with X-ray properties, we again find consistency in the relations (i.e., LX − λ and TX − λ) between the optical and X-ray selected samples.

In the second piece of analysis, I create a cluster sample based on the overlap between the XCS archive and the, as yet unreleased, preliminary DR6 cluster catalogue from the Atacama Cosmology Telescope (ACT). I use this sample to create X-ray luminosity- temperature (LX − TX), luminosity-mass (LX − M SZ) and temperature-mass (TX − M SZ) scaling relations. We find the LX − TX relation is consistent with the analysis using DES data and all three relations are consistent with the literature. I then use these derived scaling relations to search for high-redshift clusters in the ACT catalogue by exploiting a novel upper limit luminosity calculation method for candidates undetected in the X-ray regime. I find one potential high redshift cluster candidate with a lower redshift limit

estimate of z ≈ 1.4.