Galaxy Formation & Evolution PhD Projects

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

Co-evolution of the first galaxies and the intergalactic medium

Laura Keating

To study the first galaxies, we can observe them directly using telescopes such as JWST. We can also learn about these galaxies by studying them indirectly, by observing how they interact with their environment. Most of the baryons in the Universe exist in the intergalactic medium, a cosmic web of gas existing in between galaxies. As galaxies grow and evolve, they interact with the intergalactic gas surrounding them in different ways. For example, early on in the history of the Universe, the stars formed in the galaxies can emit photons that ionize and heat the gas in a process known as the epoch of reionization. Supernovae in the galaxies can also drive outflows that enrich the gas with heavier elements, such as carbon and oxygen. Measuring the ionization state and chemical enrichment of this intergalactic gas will therefore further our understanding of how the first galaxies formed. The goal of this PhD project will be to use cosmological simulations run on supercomputers to understand how the intergalactic medium and galaxies evolve together during the epoch of reionization. Existing simulations are available for analysis, but there will also be the opportunity to run your own new simulations. In particular, the project will quantify the relationship between the properties of the intergalactic medium on large scales, and the galaxies themselves on smaller scales. The simulations will be closely compared with observational data to gain new insights into the nature of the first galaxies, as well as making predictions for what will be observed with future surveys.

Exploring early galaxy evolution with JWST and ALMA

Jim Dunlop and Ross McLure

The James Webb Space Telescope (JWST) is now up and running, and in fact, performing better than anticipated. Even from the relatively small amount of public data released to date, it is clear that JWST is going to revolutionize our understanding of star/galaxy formation and evolution in the young Universe. Indeed, already our group here in Edinburgh has analysed the early-release JWST data to uncover the most distant known galaxy (at redshift z = 17), consistent with other indications that galaxy formation commenced at even earlier times than previously anticipated. The stage is thus now set for a series of major new imaging/spectroscopic studies of early galaxy evolution over the next ~5 years, using the potent combination of JWST and the Atacama Large Millimeter Array (ALMA) in Chile, bringing together near-infrared and millimetre wavelength probes of early galaxies.

 We in Edinburgh are leading the largest “Galaxies” observing programme in JWST Cycle-1 (PRIMER: PI Dunlop). This ~200-hour NIRSpec+MIRI imaging programme should complete data taking by August 2023, and so the timing will be ideal for a new PhD student, starting in September 2023, to commence analysis of the complete imaging dataset, and design JWST NIRSpec follow-up programmes in JWST Cycles 3 and 4. We also plan a major complementary programme of ALMA spectroscopic/continuum follow-up of PRIMER, to chart the rise of metals and dust in the emerging galaxy population with the first Gyr of cosmic time. This PhD project will be primarily observational in nature, but comparison with the predictions of galaxy-formation theorists/simulators (both here in Edinburgh or elsewhere) will also be of crucial importance.

The High-Redshift Galaxy Population in Galaxy Formation Simulations

Romeel Davé and Britton Smith

The James Webb Space Telescope is giving us a stunning new view of the high-redshift Universe, not only identifying the highest redshift galaxies but also revolutionising our knowledge of the galaxy and AGN population at Cosmic Noon.  These data provide new constraints on galaxy formation models, and in turn, the models can help situate these data within a cosmological galaxy evolution context as well as connect these data to multi-wavelength observations from the X-rays (New Athena) to the far-infrared (ALMA) and radio (SKA).  I am a Co-I on numerous Cycle0 and Cycle1 JWST spanning a range of science cases on high redshift galaxies, with my group's contribution primarily relating to providing comparisons and interpretations for observations using my group's latest state-of-the-art galaxy formation simulations.

The PhD student will lead some or all of these aspects of JWST work using our group's cosmological hydrodynamic simulations of galaxy formation, interfacing with international observational teams doing the PRIMER, NGST, and AURORA surveys with JWST, along with ancillary multi-wavelength data. Our main current simulation is called Simba, a highly successful state-of-the-art suite of models with unique input physics.  We are currently developing Simba's successor, Kiara, which will provide key new physical modules geared towards high-z galaxies and circumgalactic gas, as well as a large boost in speed using the new SWIFT code; Kiara is scheduled to be ready around the time this project would begin.

The student will help run and analyse Kiara simulations by adding new functionality to our existing yt/Caesar python-based analysis toolkit, and examine the properties of high-redshift galaxies tailored towards JWST and associated multi-wavelength surveys.  The student could also run additional tailored zoom simulations to examine particular classes of galaxies, or new simulations that explore the input physics.  The goal will be to not only test and refine galaxy formation models, but also to understand the nature and origin of these high-redshift galaxies and their gas and black hole constituents within a hierarchical structure formation context.  This open-ended project is ideal for an ambitious and highly motivated student with mature computing skills, who is keen to be part of the JWST galaxy evolution revolution.

Growing Pains: How do the first galaxies grow?

Sadegh Khochfar

Shortly after their birth proto-galaxies go through a growth spurt doubling their mass on very short time scales. During this violent phase of their evolution it is likely that their morphological shape and physical properties continuously change. How this change takes place, what the physical drivers are and how these first galaxies look are open questions in modern astrophysical research. These questions are very timely given the upcoming launch of the James-Webb-Space-Telescope, which will b able to probe any theoretical predictions.

This project will aim at using state-of-the-art high-resolution cosmological simulation of the formation of the first galaxies and stars to study the formation and growth of the first galaxies. The simulated data will be used to make predictions and comparisons to available observational data. The student will have access to the simulation data produced by the First Billion Years Simulation, one of the largest simulation of its kind to date. The student will also have access to a dedicated computing cluster to run additional simulations exploring different physical models.

Machine Learning Galaxy Formation

Sadegh Khochfar

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.

The spatially-resolved star formation properties of galaxies across cosmic time

Philip Best

Current studies of star formation at high redshifts are almost ubiquitously based on the ultraviolet continuum emission. However, this is heavily affected by dust extinction, giving us a biased view of star formation activity at early cosmic epochs. While alternative indicators of star formation exist, until now these have been limited in both sensitivity and angular resolution, restricting resolved studies at higher redshifts to only the most extreme systems. This Ph.D. project will use kpc-scale observations from two transformational new surveys to map out the star formation in a dust-independent manner within large samples of star-forming galaxies out to the highest redshifts. The primary goal is to trace the physical processes which drive star formation in galaxies across cosmic time, and those which cause it to cease.

'JELS' (the JWST Emission Line Survey) uses narrow-band imaging to observe (and resolve) samples of typical star-forming galaxies back to the highest redshifts (z>6), using their H-alpha emission line. This is an approved JWST Cycle 1 programme, with data due in May 2023 (and extension proposals planned for Cycle 2). The 'LoTSS Deep Fields' is a uniquely deep radio survey with LOFAR over the best-studied extragalactic fields for which observations will be completed in 2023; this will be enhanced over 2025-2026 by the 'LOFAR Ultra-Deep Observation' (LUDO); these radio observations offer the volume and sensitivity to trace the rarer starbursting galaxies across cosmic time, along with the angular resolution to resolve them. The radio and H-alpha surveys (both led from Edinburgh) are therefore highly complementary.

The Ph.D. project will build on these two observational datasets and follow-up observations. There is a wide scope of possible work, and the precise path to be followed can depend on the interests of the student.