Department Colloquium: Exploring the Dawn of the First Galaxies with PAPER and HERA

Wed, 09/10/2014 - 16:00 - 18:00
James Aguirre, UPenn

Between the surface of last scattering of the cosmic microwave background (CMB) and and the first detected galaxies at around 500 million years later lies a vast swath of unexplored history.  We know that the hydrogen in the universe was nearly completely neutral at 400,000 years after the Bang, and by a billion years later, the combined effects of the first stars, black holes, and the agglomeration of these objects into galaxies had effectively ionized all of the hydrogen in the universe, the bulk of which lies between galaxies.  Thus the history of the heating of hydrogen - via X-rays from black hole accretion or exotic physics (warm dark matter or cold dark matter annihilation) - and its eventual complete reionization by UV radiation from stars in galaxies (the Epoch of Reionization) provides an key record of the process of galaxy formation,  This history of hydrogen is traceable via emission from the 21 cm hyperfine line of hydrogen, redshifted to FM radio frequencies at the present day.  The Precision Array for Probing the Epoch of Reionization (PAPER) is a pathfinder experiment which has successfully shown how it may be possible to statistically measure the extremely faint signal from this high redshift hydrogen emission beneath the overwhelming din of emission from galaxies (including our own) between us and the Epoch of Reionization.  I will discuss my work on PAPER, and show our current best limits on the strength of this signal and discuss how this is beginning to constrain our understanding of this epoch.  I will also discuss how the approaches we have pioneered with PAPER have led to the recently-funded HERA, a next generation experiment to move beyond statistical detection and begin produce three-dimensional tomography of the universe at the dawn of galaxies. 

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