The Origins of Massive Galaxies

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The majority of stars in the present-day Universe reside in massive galaxies, primarily formed during the first six billion years prior to z = 1. Detailed studies of the processes that shaped these galaxies are critical for our overall understanding of galaxy evolution. However, observing their formation at z > 1 presents huge challenges. The OMG project will revolutionise our understanding by precisely measuring the physical properties of massive galaxies, from z = 1 back to the first billion years. This will be achieved via my leading roles in three key observing programmes using two transformative new instruments. Firstly, the James Webb Space Telescope, for which I am PI of a Cycle 1 spectroscopic programme, and a core team member of the PRIMER large imaging programme. Secondly, the Multi-Object Optical and Near-infrared Spectrograph (MOONS), for which I am a working group leader in the 200-night GTO programme. The project will also exploit my leading expertise in galaxy spectral fitting, established via my development of the widely used Bagpipes code. The OMG team will pursue three key research themes: (i) The emergence of the first massive galaxies: what are the number densities and star-formation histories of massive galaxies in the first two billion years (z > 3); do these suggest fundamental differences in star-formation physics at this epoch? (ii) The rise of massive galaxies at cosmic noon: what are the stellar ages and metallicities of massive galaxies at z = 1 - 2; do simulations accurately reproduce these properties? (iii) Morphological transformations in massive galaxies: what are the morphologies and resolved ages of z > 1 massive galaxies; how do these constrain quenching physics? In summary, the OMG team will use the latest data and analysis techniques to characterise z > 1 massive galaxies. By combining our results with state-of-the-art simulations, we will build a detailed understanding of the physics driving the formation of this key population.