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27th of April 2022
ATNF Colloquium
The photons that ionized the Universe
Emma Ryan-Weber (Swinburne)
Abstract: Less than 1 billion years after the Big Bang the hydrogen in the Universe transitioned from a neutral to ionized state. The details surrounding the Epoch of Reionization are among the biggest unknowns in modern astrophysics. Significant progress has been made in the last 5 years on when the reionization of cosmic hydrogen concluded, however we are yet to discover exactly how much ionizing radiation escapes from galaxies through to the intergalactic medium. Determining the escape fraction (fesc) of ionizing radiation is key to modelling and understanding this era. I will summarise our team’s effort on three different fronts. 1) The direct detection and characterisation of Lyman-continuum emission from galaxies just after the reionization era; 2) The lack of correlation between oxygen emission lines and Lyman continuum escape fraction; 3) IGM transmission bias and methodology for recovering the posterior probability distribution of fesc. Our observations shows that a small fraction (or during a small fraction of time or viewing angle) of Lyman continuum emitters tend to be high fesc (“on”), whereas most galaxies have fesc close to zero (“off”). The complementary theoretical work highlights the limitations of the common practice of assuming average, smooth IGM transmission functions. To finish, in a look to the future, I will introduce our plans to use a new instrument MAVIS (co-led by Australia) to measure the escape fraction of ionizing radiation from redshift 6 galaxies at the conclusion of the Epoch of Reionization.

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