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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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