Progress with PAPER: Precision Array to Probe the Epoch of Reionization

D. Backer
UC Berkeley, Astronomy Department



The first stars in the Universe ionize bubbles in the intergalactic medium and heat the surrounding hydrogen that then glows in the 21cm line. We seek to observe the spatial and frequency structure of this emission in the redshift range 7-11, which is frequencies around 150 MHz, via a power spectrum analysis a la COBE. This detection would stimulate more powerful instruments that could chart the early growth of complexity as the Universe emerges out of the Dark Ages through the Epoch of Reionization and into the Galaxy era. Our experiment is taking a step-by-step approach to the many technical challenges in making this measurement. Our instrument, PAPER, has been deployed at a test site in Green Bank, West Virginia (PGB) and, this past July in the outback of Western Australia (PWA), where terrestrial interference is minimal. Early analysis of the Australia data has led to a confusion-limited "all" sky map that has ~1 K level noise in quiet parts of the sky. This is 3 orders of magnitude above the 1 mK we need to achieve to detect the level of signals predicted by Zahn and others. Our early deployments have been with 2-8 dipoles. A 16-dipole array is now being deployed in GB; a 32-dipole array is planned for 2008 in WA. An NSF proposal for a 128-dipole array is pending.