Modelling the most extreme high redshift galaxies: from star formation rates to supermassive black hole growth

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Extremely luminous InfraRed and SubMm galaxies ((U)LIRGS and SMGs) are routinely detected with star formation rates in excess of 100 - 1000 solar masses per year at intermediate and high redshift (z>1). Morphological studies have shown that these galaxies appear to be a mix of merging/interacting systems and disk galaxies. Continuous gas accretion via cold streams has also been invoked as a means to sustain their elevated star formation rates over significantly long periods of time. Furthermore these galaxies are thought to host some of the most massive supermassive blackholes (SMBH) in the Universe, at a time when their energy input into the circum-galactic medium (so called Active Galactic Nuclei (AGN) feedback) is the largest. However, these objects have proven notoriously challenging to model, as they are very rare in the local Universe and hence necessitate running very large volume cosmological simulations whilst still resolving the interstellar medium (ISM) of the galaxy and the central region surrounding their SMBH. Making the modelling even more challenging is increasing evidence that cosmic rays and magnetic fields are strong players in galaxies with extreme star formation rates. To overcome these difficulties, this DPhil project proposes to extract a sample of rare objects from a gigaparsec cube dark matter only simulation and re-simulate them with spatial resolution fine enough to resolve the giant molecular clouds that form in their ISM, including cosmic rays and magnetic fields. Armed with this series of simulations the student will explore (i) how the environmental history of high redshift extreme star forming galaxies and the interaction between the different feedback mechanisms (stellar winds, supernovae, AGN, galactic winds possibly powered by cosmic rays) impact their star formation rates, (ii) whether ISM properties of simulated extreme galaxies match observed ones, and especially (iii) how energy is apportioned between thermal/turbulent/magnetic/cosmic ray energies and whether this regulates star formation. For this purpose, special attention will be given to outflows, in particular we will seek to determine their powering source (stellar or AGN feedback) and chemical composition (hot ionised or cold molecular gas). Comparison to spatially resolved kinematic observations will be carried out through emission line diagnostics.This research falls within STFC's science programme challenge A: "How did the Universe begin and how it is evolving?", and more specifically sub-challenges A.4: "When and how were the first stars, black holes and galaxies born?" and A.5: "How do stars and galaxies evolve?".