Project: The first luminous objects and reionisation with SPHINX

Prace Call: 17th
ID: 2018184362, Leader: Joakim Rosdahl
Affiliation: Centre de Rercherche Astrophysique de Lyon, FR
Research Field: Universe Sciences
Collaborators: Jeremy Blaizot Centre de Recherche Astrophysique de Lyon FR , Thibault Garel Centre de Recherche Astrophysique de Lyon FR , Leo Michel-Dansac Centre de Recherche Astrophysique de Lyon FR , Taysun Kimm Yonsei University KR , Martin Haehnelt University of Cambridge UK , Harley Katz University of Oxford UK , Sergio Martin Alvarez University of Oxford UK , Marius Ramsoy University of Oxford UK , Jonathan Chardin Universite de Strasbourg FR , Romain Teyssier University of Zürich CH , Lewis Weinberger University of Cambridge UK , Laura Keating University of Toronto CA , Pierre Ocvirk Universite de Strasbourg FR
Resource Awarded: 54 Mil. core hours on JUWELS


The Epoch of reionization (EoR) is a fascinating chapter in the history of the Universe. It began when the first stars formed, bringing an end to the so-called Dark Ages. As their hosting dark matter (DM) haloes grew more massive, intergalactic gas rushed in and these first stars became the first galaxies. They emitted phenomenal amounts of ultraviolet radiation into intergalactic space, which ionised and heated the atoms that make up intergalactic gas, enhancing the pressure of the intergalactic medium to the point where it may have resisted the gravitational pull of the smaller DM haloes, stunting their growth. During the EoR, the large-scale properties of the Universe were thus strongly tied to the small-scale physics of star and galaxy formation. From current observations, we can indirectly infer only limited information about this epoch, when ionised regions grew and percolated to fill the Universe about one billion years after the Big Bang. We don’t know when the EoR started, how long it lasted, what types of galaxies were mainly responsible for making it happen (such as high- versus low-mass), and how this major shift affected the subsequent evolution of galaxies in a now much hotter environment. Soon our view of the EoR will change dramatically, as in 2018 the James Webb Space Telescope (JWST) is deployed into orbit around the Sun, and in 2020 the Square Kilometre Array (SKA) comes online. Both telescopes will perform unprecedented observations of the young and far-away Universe, SKA revealing the large-scale process of reionization and JWST allowing the first robust measurements of the physical properties (stellar masses, star formation rates, abundances, clustering, ...) of a large population of galaxies during the EoR. Yet, while those telescopes will be extremely powerful, most details surrounding the interplaying physics constituting early galaxy evolution and reionization are still far out of reach observationally. To understand the physics, we need to back the limited information from observations with theory, using cosmological simulations, which combine, in three dimensions, the gravitational forces that led to the formation of galaxies, hydrodynamics and thermochemistry of the collapsing gas, star formation, supernova explosions, emission of radiation from stars, radiation-gas interactions, and gas-magnetic field interactions.  In a previous PRACE allocation in 2017, we received computing time to start the SPHINX suite of simulations, running cosmological volumes with almost two thousand resolved galaxies and their contributions to reionisation (Rosdahl+2018). We now wish to expand the SPHINX simulations to an eight times larger cosmological volume, resolving up to 15 thousand galaxies and capturing almost an order of magnitude larger galaxy masses. This unprecedented range of resolved galaxies performed with full radiation-hydrodynamics finally enables us to find out whether reionization of the Universe was powered by a plethora of low-mass dwarf galaxies, a few massive galaxies, intermediate ones, or all of the above. The simulations will aid to clear the picture and understand the underlying physics producing the wealth of data from observations in the coming years.