Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006iaujd..12e..11c&link_type=abstract
Long Wavelength Astrophysics, 26th meeting of the IAU, Joint Discussion 12, 21 August 2006, Prague, Czech Republic, JD12, #11
Astronomy and Astrophysics
Astrophysics
Scientific paper
The epoch of reionization (EoR) sets a fundamental benchmark in cosmic structure formation, corresponding to the formation of the first luminous objects that act to ionize the neutral intergalactic medium (IGM). Recent observations of Gunn-Peterson absorption toward the highest redshift QSOs, plus studies of large scale CMB polarization, and of z > 6 galaxy populations, among others, imply that we are finally probing into this key epoch of galaxy formation at z ≥ 6. However, each of these techniques is limited in its diagnostic capabilities. Observing the HI 21cm line from the neutral IGM prior to, and during, cosmic reionization is the most direct probe of this key, and as yet barely explored, phase of cosmic evolution. The HI 21cm signal depends on a number of physical parameters, including the excitation temperature, large scale structure (density fluctuations), and the ionization fraction (the `bubble machine'), and HI 21cm studies have been called the `richest of all cosmological data sets.' Potential observations include: (i) studies of small to intermediate scale structures in the IGM through HI 21cm absorption toward the first radio loud AGN and GRBs, (ii) studies of the power spectrum of fluctuations in the HI due to density and ionization structure, and (iii) ultimately, direct `tomography' of the large scale structure of the neutral IGM using the SKA. I summarize predictions for the HI 21cm signals, then consider capabilities of facilities being built, or planned, to detect these signals. I also discuss the significant observational challenges when observing at these low frequencies (< 200 MHz).
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