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The Australia Telescope National Facility Colloquium
15:30-16:30 Wed 13 Oct 2004

ATNF Marsfield Lecture Theatre

Dr Stuart Wyithe

(University of Melbourne)

Cosmic HII Regions and the Reionisation of the Universe - Dr Stuart Wyithe Colloquium

Recent discoveries of sources with redshifts greater than z~6 have
taken astronomy to the edge of the reionisation epoch. The Ly-alpha
absorption spectra of the three known z>6.1 quasars suggest an end of
the reionisation era at z~6, and reveal the presence of giant HII
regions surrounding the quasar hosts. I will show how the size of
these HII regions implies that the quasars are embedded in a
substantially neutral IGM. In future years, with the introduction of
low frequency arrays, the observational focus on the reionisation
epoch is expected to shift from Ly-alpha absorption to 21cm
emission. A substantially neutral IGM at z~6 should provide a
detectable signal for these arrays, allowing direct observation of the
boundaries of individual HII regions, as well the statistics of
fluctuations in the neutral IGM. I will show how the combined
constraints of cosmic variance and causality constrain the
characteristic angular and frequency scales on which fluctuations in
the redshifted 21cm emission will be observed at the end of

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