Gully, Harry
(2025)
From Protoclusters to Clusters: The Role of Large-Scale Structure in Galaxy Evolution.
PhD thesis, University of Nottingham.
Abstract
This thesis explores the impact of environment on galaxy evolution at high redshift, focusing on the role of environmental quenching in clusters and protoclusters. By combining deep observational data from multiple surveys with statistical analyses, this work investigates how dense environments influence galaxy star formation, mass assembly, and quenching across cosmic time. Two central questions are addressed: (1) Do the mechanisms that quench galaxies in cluster environments in the local Universe operate in the same way – or at all – in higher redshift clusters and protoclusters? (2) How do different detection methods affect samples of protoclusters and influence the derived conclusions about quenching in dense environments?
In Chapter 2, which is based on work published in Gully et al. (2025), we analyse the luminosity functions (LFs) and stellar mass functions (SMFs) of passive galaxies in four galaxy clusters at 0.8 < z < 1.3, using deep VLT data along with the GCLASS and GOGREEN surveys. We find a significant excess of faint, low-mass passive galaxies in clusters compared to the field, indicating that environmental quenching processes are already active at these redshifts. This result challenges previous findings that suggested a weaker role for environment in shaping galaxy populations at early times. Our results imply that up to 25% of the star-forming field population would need to be quenched and added to the passive population to explain the observed cluster SMF, providing strong evidence that dense environments accelerate galaxy quenching even at z ∼ 1.
In Chapter 3, which is based on work published in Gully et al. (2024) and Euclid Collaboration: Böhringer et al.(2025), we construct a new sample of protoclusters at z > 1.3 using Spitzer/IRAC colour selection, identifying 189 candidate structures across three LSST Deep Drilling Fields. Using a lightcone constructed semi-analytic galaxy formation models, we demonstrate that this method yields a pure sample (60 − 80%), but is also highly incomplete, capturing only the largest, most massive and centrally concentrated protoclusters. This work represents the first quantitative assessment of the biases inherent in Spitzer-selected protocluster searches, providing crucial insights for future studies with LSST and Euclid.
In Chapter 4, we confirm with photometric redshifts from the recently launched ESA satellite – Euclid – a sample of protoclusters drawn from the candidates detected in Chapter 3. We then analyse the SMFs and star formation properties of galaxies within these protoclusters at z ∼ 1.5. We find that while the star-forming SMFs in protoclusters and the field are remarkably similar, the passive SMF exhibits a significantly steeper low-mass slope in protoclusters, driven by an overabundance of massive quenched galaxies. Furthermore, we show that high-mass star-forming galaxies in protoclusters exhibit lower star formation rates compared to their field counterparts, suggesting that environmental quenching processes are already bringing to operate at these redshifts. While the overall quenched fraction does not differ significantly between protoclusters and the field, the distinctive shape of the passive SMF and the suppressed SFRs of high-mass galaxies indicate that large-scale structure influences galaxy evolution well before clusters fully assemble.
Overall, this thesis provides new observational constraints on how environment drives galaxy evolution at high redshift. We demonstrate that environmental quenching mechanisms are already effective by z ∼ 1, contributing to the early buildup of passive galaxies in clusters. Additionally, we refine protocluster detection techniques and characterise their biases, paving the way for future studies of large-scale structure with next-generation surveys. Finally, our results suggest that at z ∼ 1.5, environmental quenching processes begin to operate well before galaxies fully transition to a passive state. The distinct shape of the passive SMF in protoclusters highlights the role of large-scale structure in shaping galaxy evolution even before clusters fully assemble. Together, these findings refine our understanding of the role of environment in galaxy evolution.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
Hatch, Nina |
| Keywords: |
galaxies, galaxy evolution, redshift, protoclusters |
| Subjects: |
Q Science > QB Astronomy |
| Faculties/Schools: |
UK Campuses > Faculty of Science > School of Physics and Astronomy |
| Item ID: |
81369 |
| Depositing User: |
Gully, Harry
|
| Date Deposited: |
31 Jul 2025 04:40 |
| Last Modified: |
31 Jul 2025 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/81369 |
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