Cornwell, Daniel
(2025)
Cosmic Cartography: tracing the large-scale structure around galaxy clusters.
PhD thesis, University of Nottingham.
Abstract
On the largest cosmological distance scales, the cosmic web forms the backbone of the Universe. This network connects dark matter, galaxies and gas through a variety of structures. Galaxies that reside in different cosmic web environments are subject to a range of different physical mechanisms which can ultimately dictate the evolutionary path they take. At one end of the density scale, galaxy clusters exist that can quench and ultimately transform galaxies as they encounter the intracluster medium and the high density of galaxies. This results in a higher fraction of quiescent and early type galaxies in clusters compared to the field. Further down the density scale are cosmic filaments. A substantial fraction of the Universe’s mass budget is located in these environments. Filaments are a conduit through which galaxies are funneled through into the dense core of a galaxy cluster. Whilst there is strong evidence suggesting that galaxies experience environmental influence long before they reach the core of a cluster, (pre-processing), exactly where and when these changes take place is not well constrained.
Motivated by upcoming wide-field spectroscopic surveys of galaxy clusters, such as the WEAVE Wide Field Cluster Survey (WWFCS), we begin with an investigation into the feasibility of extracting cosmic web filaments around galaxy clusters with surveys like the WWFCS. We use hydrodynamic simulations from TheThreeHundred project of galaxy clusters to design mock observations for the WWFCS by taking into account observational selection effects. After extracting cosmic web filaments around galaxy clusters using the topological structures extractor DisPerSE in our mock observations, we compare them to the ‘ground truth’ simulated case. Reassuringly, we find that surveys like the WWFCS will succeed in providing detailed maps of the local cosmic web around galaxy clusters.
We then turn our attention to one of the main questions we aim to answer in this thesis: can we accurately allocate individual galaxies to different cosmic web environments? This is a crucial test: for surveys like the WWFCS to draw conclusions on how galaxy evolution is impacted by its environment, we need to know how accurately we can allocate galaxies to these environments in the first place. In order to answer this question, we design a framework where we separately use information available from simulations and from observations to classify galaxies as residing in the cluster core, filaments, and those that located in neither. Whilst we report galaxy-to-galaxy and cluster-to-cluster variations in our ability to classify galaxies, overall, characterizing filamentary galaxies is highly uncertain. However, most importantly, we outperform a random classification of galaxies to different environments. Taking into account our statistical treatment, surveys like the WWFCS will be able to draw robust conclusions on how environment shapes galaxy evolution. We also briefly discuss more recent work using Machine-Learning to drastically improve our success rates.
Having established our ability to accurately map cosmic filaments in the infall regions of massive galaxy clusters, we then consider the systematic identification of galaxy groups. Like filaments, evidence suggests that galaxy groups can preprocess galaxies prior to their accretion onto a cluster. Given that cosmic web nodes are directly identifiable through observations, we test their co-location with galaxy groups. In this study, we show a substantial fraction of massive groups that are distant from the cluster core match to cosmic web nodes. DisPerSE can therefore be used to identify both cosmic web filaments and galaxy groups with relative success.
The work in this thesis uses simulations from TheThreeHundred project to test, optimize and forecast the ability of upcoming surveys to trace the cosmic web around galaxy clusters. Along with previous studies, we pave the way for widefield optical spectroscopic surveys of galaxy clusters to extract cosmic filaments and galaxy groups.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Gray, Meghan
Aragon-Salamanca, Alfonso
Pearce, Frazer |
| Keywords: |
galaxies, galaxy clusters, cosmic web |
| Subjects: |
Q Science > QB Astronomy |
| Faculties/Schools: |
UK Campuses > Faculty of Science > School of Physics and Astronomy |
| Item ID: |
79627 |
| Depositing User: |
Cornwell, Daniel
|
| Date Deposited: |
31 Jul 2025 04:40 |
| Last Modified: |
31 Jul 2025 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/79627 |
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