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Galaxy Formation & Evolution PhD Projects

Research projects on offer in our Galaxy Formation & Evolution group:

The life cycle of gas in galaxies

Dr Kenneth Duncan and Dr Bradley Frank (UK ATC)

Galaxy evolution is regulated by the continuous cycle of gas accretion, consumption and feedback. Crucial in this cycle is the availability of the underlying fuel for star-formation; the reservoir of neutral atomic hydrogen (HI). Although measurable through radio observations, the HI 21-cm emission line is extremely faint and until recently our observations have been mostly limited to the local Universe (z < 0.2).

In this project, you will work with a new generation of surveys on the MeerKAT radio telescope (a pre-cursor to the SKA) and optical spectroscopy from the forthcoming 4MOST spectroscopic survey facility (ORCHIDSS, led by Dr. Duncan) to extend studies of the evolution of HI in galaxies to previously unexplored redshift regimes and galaxy populations. The combination of these two novel datasets will probe a huge range of critical processes in galaxy formation, so this project can follow a number of directions depending on your interests and expertise. These goals can range from making the most reliable measurement of the evolution of the cosmic HI density, mass function and fundamental scaling relations (from 0 < z < 1.4) to directly measuring the effects of AGN and star-formation driven feedback on regulating the neutral gas reservoirs of galaxies across cosmic time.

You will have the opportunity to work within a number of large international collaborations, with the potential to contribute to a range of other projects both within these teams and to follow-up observations with e.g. VLT, JWST.

Charting the growth of supermassive black holes in the young Universe

Prof James Dunlop, Prof Ross McLure, and Dr Derek McLeod

It has been known for several years now that the existence of bright quasars at redshifts as high as z~7 means that billion-solar-mass black holes were in place less than 1 Gyr after the Big Bang. The route by which such supermassive black holes came to be has been much debated by theoreticians, but such extreme objects are very rare, and until now the prevalence of more modest mass black holes at early times (potentially including the ancestors of those that power quasars) was essentially unknown.

In the last two years however, early data from the James Webb Space Telescope (JWST) has indicated that supermassive black holes may be much more common in the young Universe than previously supposed. The evidence comes from the spectroscopic discovery of broad emission lines in early galaxies (indicative of active galactic nuclei: AGN) and from the discovery of an apparently new population of very compact, red objects (termed "little red dots") which may be dust obscured AGN.

However, at present the situation is very confused. Many early galaxies are known to be compact, and broad emission lines can result from the outflows produced by intense star-formation activity. At high redshifts it is also a major challenge to reliably separate the unresolved light from an active black hole from the starlight in its host galaxy, even with the exquisite resolution of JWST.

This observational project aims to sort out this situation through a multi-pronged approach. Existing and imminent JWST NIRCam, MIRI and NIRSpec data will be used to clarify which early galaxies host AGN, and to properly determine their black-hole and host-galaxy masses. This will be achieved by using MIRI to search for warm (AGN-heated) dust, using NIRSpec to obtain spectroscopic estimates of black-hole mass, and by carefully analysing the highest resolution NIRCam data to better constrain the relative contributions of nuclear and extended light in high-redshift galaxies. Deep stacking of X-ray data and of the growing wealth of new radio data may also be explored, to provide a more complete multi-frequency perspective.

Machine Learning Galaxy Formation

Prof Sadegh Khochfar

Video: Machine Learning Galaxy Formation
IfA PhD Projects

In this project, we want to develop new machine-learning algorithms to investigate galaxy formation in the Universe. The algorithms will be applied to numerical simulations of galaxy formation in a first step and then used on observations. The idea is to break degeneracies between simulations and models used in the community and to identify the most important astrophysical drivers of galaxy formation. The student would work with data sets available in the group and from international collaborations.

Establishing the growth of early UV-emitting galaxies, and their role in reionizing the Universe

Dr Derek McLeod, Prof James Dunlop, and Prof Ross McLure

With the advent of the James Webb Space Telescope (JWST) and its mid-infrared capabilities, we have made remarkable progress in the study of cosmic star formation history at z>9, with evidence of significant star formation taking place even ~400 million years after the Big Bang, beyond the observational horizon of the Hubble Space Telescope (HST). However, there has been limited recent progress in our understanding of the demographics of the UV-brightest galaxies in the epoch of reionization (i.e. z~6-10) beyond what has been achieved through wide-area (but lower resolution) ground-based works combining the VISTA and Subaru telescopes, or HST+JWST legacy fields covering modest search areas of ~400 sq. arcmin. Moreover, there has been limited progress in investigating the very faintest galaxies in the epoch of reionization, with the current state-of-the-art z=6-7 UV luminosity function (UV LF) determinations still being from the pre-JWST era.

This observational PhD project presents an excellent opportunity to address these gaps. Firstly, the upcoming HST CLUTCH survey will provide ~0.5 sq. degrees of HST imaging at optical wavelengths - when combined with the JWST surveys COSMOS-Web and COSMOS-3D, this will provide an unprecedented area of space-based imaging with which to investigate UV-bright, reionization-era galaxies. This project will involve leveraging this exquisite dataset, along with other key legacy HST+JWST data sets, in order to determine the evolution of the bright-end of the UV LF from Cosmic Dawn to the end of reionization. The brightest objects uncovered will provide excellent targets for follow-up spectroscopy with JWST NIRSpec and with ALMA. There will also be an opportunity to investigate their morphologies, and the prevalence and impact of merging systems on our understanding of the bright-end of the LF.

Secondly, there is an incredible opportunity to utilise numerous existing ultra-deep imaging surveys to investigate the UV-faintest galaxies in the epoch of reionization. This PhD project will look to leverage the remarkable gravitational lensing power of numerous galaxy clusters, including from surveys such as GLIMPSE, UNCOVER and CANUCS, to probe intrinsically UV-faint z=6-10 galaxies at M_UV >= -16. These observations will provide crucial constraints on the extreme faint-end of the UV LF from Cosmic Dawn to the end of reionization. This project will not only allow us to understand the nature of extremely UV-faint galaxies, but also their overall contribution to cosmic reionization.

Exploring galaxy evolution from reionization to cosmic noon with JWST

Prof Ross McLure, Prof James Dunlop, and Dr Derek McLeod

Over the last three years, the unprecedented sensitivity of JWST has transformed our understanding of galaxy evolution at high redshifts. We now know that galaxy formation was already well established by z = 14 (only 300 Myr post Big Bang), chemically mature galaxies existed by z = 7 and full-scale quenching of star formation was underway by z = 5. Moreover, JWST has also revealed the obscured progenitors of the local population of supermassive black holes, many of which reside in so-called 'little red dots' at z > 4.

This PhD project will initially focus on exploiting the latest JWST imaging data to derive a state-of-the-art measurement of the galaxy stellar-mass function (GSMF), from cosmic noon through to the epoch of reionization and beyond. A key constraint of galaxy evolution models, in combination with the dark matter halo mass function, the GSMF will reveal how star-formation efficiency evolves with redshift and the impact of high-mass/AGN feedback processes. In addition, the sensitivity and spatial resolution of JWST will enable a detailed study of how the morphologies of galaxies evolve with redshift. In combination with star-formation history constraints from SED modelling, this morphological information will help to differentiate between different quenching models and quantify the impact of dust attenuation and merger activity.

By comparing state-of-the-art observational constraints with the latest generation of hydrodynamical simulations, the overall goal of the project is to enhance our understanding of the evolutionary pathways linking local galaxy populations with their high-redshift progenitors.

Under the Active Galactic Nuclei projects, see also:

Under the Computational Astrophysics projects, see also:

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