Seminarium: Constraining Cosmic Reionization

We cannot yet see “Cosmic Dawn”, when the very first stars and galaxies lit up the Universe. These objects are too faint and rare, and their light is redshifted beyond the reach of current telescopes. However, these first galaxies fundamentally altered their surroundings - transforming cool, atomic, intergalactic hydrogen to a hot plasma. This “Reionization” process depends on the interplay between poorly understood astrophysics of galaxy formation and the unknown nature of dark matter on small scales, and thus constraining how Reionization happened is key to understanding the underlying physics. I will describe how we can constrain the Reionization process from current observations, using the transmission of Lyman alpha photons in the intergalactic medium, by comparing spectroscopic samples of galaxies to simulations using statistical inference methods. I will present measurements which favour a late and relatively rapid reionization, and place these in the context of high redshift galaxy formation, and discuss the prospects of future facilities, such as the James Webb Space Telescope and upcoming 21 cm experiments, to fill in our cosmic origin story.

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We shall take the speaker to lunch at 12:25. There will be fika after the seminar.