The Epoch of Reionisation is the period in the early Universe between about 200 million and 1 billion years after the Big Bang. During this epoch, the very Birst stars and galaxies formed and started to eat away at the fog of neutral gas that pervaded the cosmos. Detecting and characterizing these Birst galaxies in one of the main goals of upcoming facilities such as NASA/ESA’s James Webb Space Telescope, and the European Large Telescope, and is already being probed with the Hubble Space Telescope and ESO’s Atacama Large Millimetre Array (ALMA). Simulations such as Simba, run on cosma-7 at Durham, are a critical tool for situating such data within a cosmological context and exploring the underlying physical drivers.
Harvard graduate student Xiaohan Wu, with project PI Romeel Davé at Edinbugh, used the Simba simulation suite to explore the physical and observable properties of EoR galaxies as will be seen by Hubble and Webb. Wu et al. (2020) showed that Simba produced galaxies with sizes and photometric colours in very good agreement with existing Hubble observations, and then made predictions for the sort of improvements that will be seen using Webb (to be launched in 2022). The image below shows redshift 6 simulated galaxies “observed” with Hubble in 3 bands (top row), and with Webb (bottom row). The improvement is stark, and enables detailed studies of the assembly history of early galaxies.
In a separate work, Cornell student Daisy Leung worked a group including PI Davé to use the same Simba suite to study the far-infrared properties of EoR galaxies as would be observed with ALMA (Leung et al. 2020). To do so, she applied a new far-IR line radiative transfer code called SÍGAME to Simba outputs, creating the Birst ensemble of [CII] line emission images from a cosmological simulation in the EoR, and the Birst predictions of the [CII] luminosity function that might be detected with a large ALMA program, or future proposed far-IR observatories such as NASA’s Origins. These results illustrate Simba’s capabilities to make making multi-wavelength predictions for EoR galaxies that can help guide and interpret present and future observations of the Birst billion years.
