From Crisis to the Solution of Cosmic Reionization

by Koki Kakiichi (Cosmic Dawn Center, University of Copenhagen)

Wednesday 28 Oct 2026, 13:30 → 14:30 Europe/Stockholm

FC 61 (AlbaNova Main Building)

JWST has revealed many challenges to our understanding of the early Universe. In this talk, I will present my view on where we stand and explore how we can move toward solving the problem of cosmic reionization. I will begin by highlighting the importance of reionization as a central challenge in early-Universe astrophysics and cosmology, and argue that JWST, together with wide-area observatories, now provides a full spectrum of tools required to make progress. I will showcase a reionization tomographic mapping experiment using a wide-area JWST+Subaru survey to observationally visualise the 3D structure of reionization—a map we have long simulated but never imaged directly. I will also discuss lessons learned from spectroscopic galaxy surveys in z > 6 quasar fields about what reionized the Universe. In addition, I will discuss the physical processes regulating the escape of ionizing radiation from galaxies and their implications for the onset of reionization at z > 10. Finally, I will argue that cosmic reionization has now become a well-defined solvable problem, providing a crucial foundation for realizing the full potential of 21-cm cosmology in the 2030s and beyond.