Galaxies, Active Galactic Nuclei and Cosmology

Chiaki Kobayashi, Christopher Lovell, Jim Geach

Just after the Big Bang, the First Stars form, and cause the First Enrichment in the Universe when they die. What is the nature of the First Stars? How massive are they? Which elements were produced? When do we have enough elements to form a life? The student will answer these questions by using computational simulations to follow the chemical and dynamical evolution of galaxies across Cosmic Time. Our simulation code already includes relevant physics of atomic matter - hydrodynamics, star formation, chemical enrichment from Type II and Ia supernovae, and feedback from supernovae and supermassive black holes - and therefore, the predictions are comparable with observations from nearby to distant galaxies. The student will update the code to include additional stellar physics of the First Stars (such as pair-instability supernovae or black-hole-forming faint supernovae) and study the First Enrichment in a fully cosmological context, for the first time in the world. The simulation predictions will be compared with brand new observational data from the James Webb Space Telescope.

Kristen Coppin, Jim Geach, Maximilien Franco

Over half of the star formation energy generation in the Universe is extincted at optical wavelengths and enshrouded by dust which absorbs and re-radiates the starlight in the far-infrared/submm; and the sub-mm and mm atmospheric windows allow us to access the redshifted far-infrared emission from this obscured or ``hidden’’ side of galaxy formation and evolution.  The James Clerk Maxwell Telescope (JCMT) Cosmology Legacy Survey (S2CLS; Geach et al. 2017) and its extension via the SCUBA-2 COSMOS survey (S2COSMOS; Simpson et al. 2017) and now S2XLS (PI Geach) and STUDIES (Wang et al. 2017) are the largest and most sensitive and ambitious single-dish surveys at 850 and 450 micron (in the submm wavebands) ever conducted.  In addition, the 50-m Large Millimeter Telescope in Mexico will be conducting unique and transformative imaging of the sky at millimeter wavelengths through a series of public Legacy Surveys (Ultra-Deep and Large Scale Structure surveys in particular) during 2020 using the new TolTEC camera.  These unprecedented legacy surveys have been yielding thousands of high-redshift galaxies selected in the sub-mm/mm wavebands - providing an order-of-magnitude improvement in the sample sizes of previous surveys at these wavelengths!

With so much data now in-hand there are several possible projects that could be carved out using a combination of these legacy (sub)mm surveys with existing ancillary multi-wavelength data to make progress on a key outstanding question in galaxy evolution: How are dust and metals built up in massive galaxies over cosmic time? Some key science that could be explored with these data sets by a keen student include (for example): 1) constraining the (sub)mm source counts beyond the confusion limit (using a statistical P(D) fluctuation analysis); 2) locating and probing the high-redshift tail of the distribution of (sub)mm galaxies (via new mm observations); and 3) exploring new parameter space on the dust content, obscuration fraction, and gas content in galaxies (via (sub)mm observations) as a function of mass out to much higher-redshift than has previously been explored.  The project can be tailored to some degree to match the student’s interests and skill set.

We are also involved in ongoing efforts to perform detailed follow-up of these high-z submm-detected sources at higher resolution with the Atacama Large Millimetre Array (ALMA) situated at 5000m on the Chajnantor plateau in Chile.  It is envisaged that the findings of this work will feed naturally into new ALMA and other telescope proposals, such as the James Webb Space Telescope (JWST).

Martin Krause, Martin Hardcastle

The evolution of galaxies and their central supermassive black holes is closely linked and evidence is accumulating that the mutual interaction is different for different galaxies and in different epochs of the Universe. The black holes produce powerful radio jets that may affect star formation in galaxies, in particular, via preventing cooling gas around the galaxies from arriving in the galaxy in the first place and also by triggering star formation by compressing dense gas already inside the galaxies. Our group has contributed to this progress with simulations in the past. This PhD project would use existing simulation software to study jets in galaxies with a star-forming disc, similar to the Milky Way. The jets are expected to form radio lobes, affect outflow properties of the gas and the rate of star formation. Such results will then be compared to observations available within the group and from the literature. This will result in a better understanding which observations may be explained by jets and how important this jet feedback really is in star-forming galaxies.

Daniel Smith

Starting in 2021, the WEAVE-LOFAR survey will use the new WEAVE multi-object spectroscopic facility on the William Herschel Telescope to obtain spectroscopy of radio sources identified in the new LOFAR Surveys. The LOFAR surveys have the best combination of huge sensitivity, resolution and sky coverage, and they are already revolutionising our understanding of the Universe. However, WEAVE-LOFAR is the key for taking this to the next level, by providing the most accurate redshifts, source classifications and the most inclusive sampling of the active sources in the Universe. Over the coming five years WEAVE-LOFAR will generate a huge library of optical spectra, and this is the first time that spectroscopy of radio sources has been done on this scale - giving WEAVE-LOFAR access to a huge discovery space. This PhD position is ideally-timed to get your hands on the first data from WEAVE-LOFAR, and join the team writing the first publications. Lots of different directions are possible, including studying star formation evolution in galaxies over the last half of cosmic history, searching out and characterising the most star-forming galaxies in the Universe, or making new measurements of the influence of accretion by black holes on galaxy evolution. The possibilities are virtually endless. If this sounds like something that would interest you - please do get in touch.