The evolution of galaxies in the early universe with the next generation of telescopes

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Oct. 3, 2021

March 31, 2025

At the cutting-edge of Astronomy research is the study of the formation and evolution of the first galaxies. Through breakthrough observations in the past 30 years it has been possible to identify galaxies from when the universe was less than 500 million years old. These galaxies have unusual properties compared to the local universe, showing low chemical enrichment and dust obscuration, and irregular morphologies. The majority of studies of early galaxies to date have focused on 'typical' galaxies at that epoch, using deep pencil beam Hubble Space Telescope observations. These low mass, common high-redshift sources have been well studied however there is a lack of knowledge about the high mass end of the population. This project focuses on exploiting the current best datasets for understanding these bright, high mass galaxies. It is these rare and bright sources that are expected to be the sites of the earliest chemical enrichment and dust production in the early Universe. Furthermore, they are predicted to pinpoint the highest density environments. At z = 7, within the Epoch of Reionization, it is thought that the highest density regions will also be the most ionized, as both the central and associated/satellite galaxies produce ionizing photons that generate bubbles in the otherwise neutral Inter-galactic medium. Finally, simply the number density of the most massive sources provides key constraints on galaxy evolution, as it is these sources that are the hardest to produce in simulations. The role of AGN feedback, mergers and the star-formation efficiency in low-metallicity environments could all have a large impact on whether high SFR or mass galaxies can exist in the first billion years.

Aims and objectives

This project aims to exploit the current best wide-area datasets to find and study galaxies at high-redshift. At the end of the project the student will use the first data from the Vera Rubin Observatory (VRO) and Euclid space-mission to extend this research, putting them in an excellent position for future research if they choose this. The goal of the project is to understand when and how the most star-forming galaxies formed in the Universe. The student will become an expert in the selection of high-redshift galaxies from multi-band photometry. They will then use the resulting samples to constrain the evolution of the number density of these sources (via the luminosity function). To understand the astrophysics, these derived luminosity functions will be compared with a range of cosmological galaxy evolution models.

The PhD can be split into 3-4 projects, all of which should lead to publications. In the first project the student will analyse the best available ground-based wide area surveys to search for z = 7 galaxies. This has not been done before using the VIDEO survey. Specificially they will pixel match the Subaru Hyper-Suprime Cam optical imaging to the VIDEO data in the XMM-LSS and CDFS fields. They will produce catalogues from these images, and do a robust Spectral-Energy Distribution fitting analysis to search for z = 7 candidates. The candidates will then be carefully inspected to remove any artefacts or contaminants (e.g. brown dwarfs). Once a final sample has been defined the student will compute the rest-frame UV luminosity function at these redshifts, extending this to very bright absolute magnitudes. The research method will build upon previous experience in the field. The luminosity functions will be analysed with a novel method that does not use binning (kernel density estimator). This will result in a strong first author publication.

For the next 2-3 projects there are several options depending on the state of the field at this point, guided by the student's preference. I outline briefly the different projects below.

1) Clustering analysis of high-redshift samples, to determine the likely halo masses and to study the star-formation efficiency as a function