Institute for Astronomy

Galaxy Formation & Evolution PhD Projects

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

Exploring the formation of the first galaxies with VISTA and JWST

James Dunlop and Ross McLure

Video: Exploring the formation of the first galaxies with VISTA and JWST
Exploring the formation of the first galaxies with VISTA and JWST

Understanding “first light”, the very early formation and evolution of galaxies of stars, is one of the key goals of modern astrophysical cosmology. Although current studies have pushed back in cosmic time to less than 1 billion years after the Big Bang, the first galaxies have yet to be seen. This is in part because observational facilities such as the Hubble Space Telescope cannot observe at sufficiently long infrared wavelengths to detect objects that have been redshifted beyond z = 10. Over the next few years this situation is set to change dramatically, first with completion of UltraVISTA (the deepest ground-based near-infrared survey) in Spring 2022, and then with the advent of deep near/mid-infrared observations with the James Webb Space Telescope (JWST) (first data expected mid 2022 following launch in late 2021). This project will focus on the use of the deepest infrared survey imaging data from UltraVISTA and then from JWST to reveal the very early formation and growth of galaxies, potentially reaching out to z ~ 20, into the epoch when the first stars are predicted to have formed. Given the above timescales, Sept 2021 is the ideal time for a postgraduate student to commence work in this area, with access to UltraVISTA data guaranteed (J. Dunlop is PI) and early JWST NIRCam imaging data anticipated both from Edinburgh-led surveys and from public Early Release Science programmes ~6 months after launch. The project is primarily data driven, but will also involve detailed comparison with the predictions of galaxy formation simulations being produced here in Edinburgh and elsewhere.

Galaxy Transformation in Simba Zoom Simulations

Romeel Davé

Video: Dave video
Dave video

Understanding how galaxies transform from star-forming spirals to quenched ellipticals is one of the key questions in modern galaxy formation theory.  The answer likely lies in some combination of environment, merging, gas consumption, and feedback from active galactic nuclei.  Cosmological galaxy formation simulations that include all these processes are crucial for understanding how galaxies transform.  Our Simba simulations produce unsurpassed agreement with observations of the quenched galaxy and AGN population, making it an ideal platform for exploring the physics that drives galaxy transformation.

A student is invited to lead our group's next stage of simulations to explore the critical galaxy group scale where transformation occurs.  This will involve running a suite of group-scale zoom simulations using the latest Simba input physics, and using this to understand the relationship between morphological transformation, color transformation, and quenching.  The student will employ our extensive python analysis suite to make comparisons to a range of present and upcoming observations over cosmic time, including making predictions for upcoming X-ray and Sunyaev-Zeldovich telescopes.  Then they will investigate the key physical drivers by conducting numerical experiments turning on and off individual physical processes, as well as investigating how energy input from AGN relates to quenching.  The goal is to produce a coherent theoretical scenario for how galaxies quench as a function of mass, epoch, and environment, and highlight the most pressing questions to be pursued with upcoming multi-wavelength facilities. 

Cross-listed with Simulations.  Familiarity with C and Python is highly recommended.

Galaxy Formation and Cosmology Using the Equilibrium Model

Romeel Davé

Though the physics of galaxy formation is incredibly complex, a heuristic description of galaxy formation turns out to be remarkably simple.  This is encapsulated in our "equilibrium model" (Dave et al. 2012; Mitra et al. 2015), based on a mass balance equation with free parameters that quantify baryon cycling.  Using only 10 free parameters (far fewer than traditional semi-analytic models) constrained via Bayesian MCMC, it fits the observed scaling relations of stellar, metal, and satellite growth within galaxies and halos across much of cosmic time, including the scatter around these relations.  Current work is extending this framework to operate within N-body merger trees, and populate halos using machine learning.

A student is invited take the lead on this project to utilise and/or extend the equilibrium model: (i) Improve constraints on dark energy from upcoming large-area surveys such as DES, LSST, and Euclid by using the robust Bayesian posteriors provided by the equilibrium model; (ii) Understanding the physical implications for feedback processes in galaxy formation by comparing equilibrium model baryon cycle constraints with that from hydro simulations; (iii) Extending the equilibrium model to include black holes, neutral gas, molecular gas, and galaxy shapes. 

Cross-listed with Cosmology.  Familiarity with C, Python, and machine learning techniques is useful.

 

An unbiased view of the drivers of cosmic star formation

Philip Best & Ken Duncan

Video: An unbiased view of the drivers of cosmic star formation
An unbiased view of the drivers of cosmic star formation

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, requiring large and uncertain corrections, and potentially giving us a biased view of galaxy formation and evolution at early cosmic epochs. This Ph.D. project will use alternative, dust independent, techniques to construct and study large samples of star-forming galaxies out to the highest redshifts in an unbiased manner, with the goal of revealing the physical processes which drive star formation in galaxies, and those which cause it to cease. The project will begin with detailed analyses of a sample of around 100,000 star-forming galaxies identified in the 'LoTSS Deep Fields': a uniquely deep radio survey with LOFAR over the best-studied extragalactic fields, being led in Edinburgh. Together with new optical spectroscopy of these sources from the WEAVE-LOFAR survey (in which Edinburgh plays a key role), this will enable the dependence of star formation activity on galaxy mass and environment to be studied in a dust-independent manner out to beyond the peak epoch of star formation activity at z~2, as well as providing samples of starbursting galaxies out to the highest redshifts. In later years we aim to exploit JWST narrow-band imaging to derive samples of H-alpha-selected star-forming galaxies back to the highest redshifts (z>6), forming an ideal complement to the radio samples. We also plan to exploit a new spectroscopic survey of moderate-redshift radio sources with 4MOST to study the manner in which neutral (HI) gas drives star formation activity.

This project can be funded either as a normal UK PhD, or through the new Edinburgh-Leiden joint studentship scheme, where the student would spend 1-2 years of their PhD in Leiden, working under the joint supervision of Huub Rottgering. Leiden is the lead institute in LOFAR Surveys, and a major partner in WEAVE-LOFAR.

The Origin of Super-Massive Black Holes in the Universe

Sadegh Khochfar & Joop Schaye

Video: Origin of super-massive Black Holes
Origin of super-massive Black Holes

The 2020 Nobel Prize in physics was awarded for the discovery of the super-massive black hole at the centre of our galaxy and the confirmation that black hole formation is the necessary outcome of gravitational collapse in general relativity. While there is very little observational doubt that black holes as massive as 1 billion solar masses already exist some hundred million years after the Big Bang, we still do not know how they are seeded in the first place. Several different physical mechanisms have been proposed, and the aim of this PhD project is to investigate these using state-of-the-art numerical cosmological hydrodynamics simulations.

The project will in a first step focus on the formation of massive black hole seeds in dense star clusters. Such environments promote the collision of stars and the subsequent formation of massive black holes and their feeding via tidal disruption events. Question we would like to answer include, can such seeds form and grow fast enough, what gravitational wave signals do they emit and what other observational signatures do we predict in the early Universe. The latter is very topical given the imminent launch of the James-Webb Space telescope in 2021 and a unique opportunity to provide testable predictions.     

As part of the project the student will join an international collaboration working on the next generation of numerical simulation code SWIFT and can spend 1-2 years of their time in the group of Prof. Joop Schaye in Leiden

Growing Pains: How do the first galaxies grow?

Sadegh Khochfar

Video: Growing Pains: How do the first galaxies grow?
Growing Pains: How do the first galaxies grow?

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.

Dust in the universe

Sadegh Khochfar & Ross McLure

Video: Dust in the Universe
Dust in the Universe

Observations of galaxies rely on the information carried by photons to us. Dust in galaxies absorbs and scatters photons from our line-of-sight reducing the amount of photons reaching us and thus obscures the intrinsic properties of galaxies. While we know how to produce dust in galaxies, we still do not know how dust evolves in the habitat of a galaxy. Several physical mechanisms have been proposed that destroy dust. In this project we the student will use high resolution numerical simulations including state-of-the-art models for the production and destruction of dust and make predictions for its evolution. These predictions will be very timely and used to make comparisons to observations of the first galaxies in the Universe with  the James-Webb-Space-Telescope  and the ALMA observatory. Besides running state-of-the-art numerical simulations on super-computers the student will also work closely with observers to make testable predictions. 

Under Computational Astrophysics projects, see also:

  • A new cosmological residual distribution hydrodynamical solver Sadegh Khochfar

Under Milky Way & Local Group projects, see also: