About
I am a Reader (Associate Professor) in Galaxy Evolution at the University of Edinburgh, based at the Institute for Astronomy. My work focuses on the chemical evolution of galaxies across cosmic time, the properties of metal-poor stellar populations, and the search for — and characterisation of — the first galaxies.
I use a combination of imaging and spectroscopic surveys, including data from JWST, to trace how galaxies form, enrich their gas with heavy elements, and evolve from the earliest epochs of the Universe to the present day.
Research interests
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Chemical evolution
Our group is interested in studying the chemical enrichment of galaxies across cosmic time in order to understand their star-formation histories and help to constrain the key physical processes of the galaxy baryon cycle. Some of our most recent papers:
- Electron temperature relations and the direct N, O, Ne, S and Ar abundances of 49,959 star-forming galaxies in DESI Data Release 2 — Scholte et al. (2026)
- The JWST EXCELS survey: direct estimates of C, N, and O abundances in two relatively metal-rich galaxies at z ≃ 5 — Arellano-Córdova et al. (2025)
- The JWST EXCELS Survey: gas-phase metallicity evolution at 2 < z < 8 — Stanton et al. (2026)
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Metal-poor stellar populations
Understanding the properties of the massive stars that formed in the extremely metal-poor environments of the early Universe is crucial for understanding the chemical enrichment of the first galaxies, early stellar feedback processes, and the process of reionization. Our group uses deep JWST spectroscopy to constrain the properties of the earliest massive stellar populations.
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The first galaxies
The launch of JWST has pushed the redshift frontier of galaxy evolution out to z=15. Our group is heavily involved in the search for — and characterisation of — galaxies at the earliest cosmic epochs.
- The ultraviolet continuum slopes (β) of galaxies at z ≃ 8–16 from JWST and ground-based near-infrared imaging — Cullen et al. (2023)
- The ultraviolet continuum slopes of high-redshift galaxies: evidence for the emergence of dust-free stellar populations at z > 10 — Cullen et al. (2024)
- A search for the first galaxies across >0.6 deg² of JWST imaging: new evidence for a rapid decline in star-formation activity at z > 12 — McLeod et al. (2026)
Publications
Data
VANDELS FUV M* stacked spectra — Rest-frame FUV composites at 2.5 < z < 5 from Cullen et al. (2019). Stacked in seven stellar mass bins (see Table 1 of Cullen et al. 2019).
VANDELS FUV Lyα stacked spectra — Rest-frame FUV composites at 3 < z < 5.5 from Cullen et al. (2020). Stacked in bins of Lyα equivalent width (see Cullen et al. 2020).
Research Group
Current
- Dirk Scholte — Postdoc
- Cecilia Bondestam — PhD student
- Evan Jones — PhD student
Past
- Thomas Stanton — PhD student → Postdoc, IfA Edinburgh
- Ryan Begley — PhD student → Öpik Research Fellow, AOP
- Karla Arellano-Córdova — Postdoc → Postdoc, CEFCA Teruel
Studentships & Fellowships
PhD studentships
Each year the IfA advertises PhD studentship opportunities, usually listed in November/December with applications due the following January. If any of the topics above are of interest, please feel free to get in touch — you can also check whether I currently have a project on offer via the IfA's PhD & Research studentships page.
Fellowship Opportunities
Each year there are also a number of postdoctoral fellowship opportunities. Most of these are subject to internal selection, and the internal deadlines fall well ahead of the official fellowship deadlines, so early contact is encouraged. If you're interested in applying for a fellowship at Edinburgh, please feel free to get in touch for information and advice — further details can be found on the IfA Fellowships page.