PI: Harley Katz
The first billion years of cosmic history witnessed the birth of the first galaxies, the enrichment of the interstellar medium with heavy elements, and the reionization of the Universe. While JWST is now revealing glimpses of this era via deep imaging and spectra, interpreting this data requires sophisticated theoretical models that self-consistently track the interplay between radiation, gas chemistry, and star formation.
PRISM-XL (codename MEGATRON) is a new suite of high-resolution cosmological radiation hydrodynamics simulations of Milky Way mass galaxies designed to bridge this gap. The simulations are the first to self consistently couple on-the-fly radiation transport to a large chemical network of primordial species, metals, and molecules, allowing us to directly predict the observable properties of galaxies in the high-redshift Universe. Moreover, these simulations vary key physical processes—such as star formation efficiency, feedback strength, and the stellar initial mass function—to predict the observable consequences of different galaxy formation scenarios. PRISM-XL explores four interconnected science cases: (1) the onset of star formation at Cosmic Dawn, (2) the assembly of early galaxies and their interstellar medium during the Epoch of Reionization, (3) the properties of the circumgalactic medium towards Cosmic Noon, and (4) the fossil record of reionization imprinted in nearby dwarf galaxies.
By leveraging >50 million CPU hours on DiAL 3 and Cosma8, PRISM-XL provides synthetic spectra for >200,000 galaxies that can be directly compared with JWST data. Figure 1 showcases the four scientific themes of the project using real images from the simulation. We show the first oxygen emission after the transition from metal-free to metal-enriched star formation (top left), a disk-like galaxy and its emission lines 400 Myr after the Big Bang, highlighting galaxy formation in the reionization epoch (top right), emission from the diffuse gas at z = 4 demonstrating the ability of the simulations to resolve the circumgalactic medium (bottom left), and a dark matter map of the galaxy at z = 0, representing the connections that can be made from high-to-low redshift with regards to near-field cosmology.