Dissecting galaxies at the cosmic dawn

Contemplating our origins is a key part of what makes us human, and has provoked ideas and stories in every civilisation. My research is similarly motivated by this curiosity. I am driven by questions such as: How were stars and galaxies first formed after the creation of the Universe in the Big Bang? How did they differ from those we see around us in the local Universe? When were the elements necessary for life, such as oxygen, carbon and nitrogen, first created? The formation of the first stars and their assembly into the first galaxies is now a frontier focus of modern physics, and the subject of intensifying research activity.

Owing to the finite speed of light, we see galaxies farther back in time by observing more distant examples. The scrutiny and refinement of models of structure formation in the early Universe therefore requires direct observation of the most-distant galaxies. The installation in 2009 of new instrumentation aboard the Hubble Space Telescope (HST) enabled it to detect starlight that travelled across the cosmos for 13.4 billion years, emitted from galaxies seen only 400 million years after the Big Bang. These remarkable observations proved that galaxies, and the elements needed for life, were present mere moments into cosmic history.

Hubble's forthcoming successor, the James Webb Space Telescope (JWST), aims to discover the forebears of these systems and characterise the physical processes governing the growth of the very first generation of galaxies. Due to launch in 2021, JWST's instruments will reveal galaxies seen 100 million years after the Big Bang. Over the next five years I will exploit the world's premier ground-based telescopes, and JWST, to answer fundamental questions such as: When did the first stars and galaxies form? How rapidly did the first galaxies evolve, and which physical processes regulated their growth? Which galaxies were responsible for ionising the intergalactic neutral hydrogen that pervaded the early Universe? Did the stars within galaxies dominate this process, or was it driven by the first population of black holes?

My analyses will deliver measurements of the fundamental diagnostic quantities that describe the formation and evolution of the first galaxies. They will thus enable refinement of galaxy evolution models in a regime that is at present wholly unconstrained by observations. Such measurements are the crucial ingredient needed to foster the next major development in our understanding of the structures that first illuminated the cosmos.