PI: Romeel Davé
The Epoch of Reionization (EoR) is the period of cosmic time over which the first stars and galaxies appeared, whose heat and energy caused hydrogen gas in the cosmos to become ionized. It is regarded as the final frontier of galaxy evolution studies, where galaxies like our Milky Way were first seeded. Thanks to the James Webb Space Telescope, the EoR is now able to be observed with unprecedented detail, prompting great interest in the simulation community to model all the complex processes involving both galaxy growth and radiative transfer self-consistently within a cosmological context.
We are working on a new suite of galaxy evolution simulations called Kiara, which is a successor to the Simba suite run on cosma7 in 2018 that has been highly utilized in the community. Kiara is a totally new model with many improvements to Simba, now embedded in the SWIFT code. While developing Kiara, we are simultaneously developing Kiara-RT, the fully radiative hydrodynamic version of Kiara. This DiRAC allocation has been instrumental in developing, testing, and calibrating Kiara and Kiara-RT.
As a sneak preview, we present below snapshots of the neutral fraction within a cosmological volume approximately 18 comoving Mpc on a side, at various redshifts. One can see how the ionizing photons are escaping from the galaxy in order to re-ionize the universe, the growth of the associated ionizing bubbles, ending with a mostly ionized universe by redshift 6. This arises from UV photons emitted by massive stars whose formation is self-consistently modeled within the simulation. Understanding how reionization proceeds and impacts both galaxies and intergalactic gas is a central goal of EoR studies, and simulations like Kiara-RT are vital in assembling various multi-wavelength observations into a consistent story for how this critical cosmic epoch proceeded.
The growth of ionized bubbles in a cosmological Kiara-RT simulation from early stages of the EoR to near-final reionization (z=8-6), driven by photons from young stars propagated through an expanding inhomogeneous neutral intergalactic medium.