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The Cosmic Deep And Wide Narrowband (Cosmic DAWN) Survey


The Cosmic DAWN Survey is a definitive test for the neutral gas fraction near the epoch of reionization using a survey of Lyman-alpha emitters at z = 7.7. The redshift of reionization, its speed, and its homogeneity are unknowns, with the Gunn-Peterson tests probing the end of reionization at z > 6, while WMAP suggests that this occurred at z ~ 11. Ly-α galaxies provide a powerful tool to probe the central phase of reionization with neutral fractions of gas ≈ 50% because the Ly-α photons scatter resonantly. The observed Ly-α luminosity function (LF) should then show a substantial decline. The Cosmic DAWN investigators pioneered the use of Ly-α emitters to show that the IGM is more than 50% ionized at z = 6.5 (Malhotra & Rhoads 2004). The present survey uses 40 nights of deep narrowband imaging in 4 fields to find Ly-α line emitters. Ly-α are found by differencing NEWFIRM images taken in a 3.5nm wide filter at 1066nm with broad J-band images. The expected yield 40 Ly-α emitters, or 10 in each field, if the IGM is ionized at z = 7.7. The four fields guard against cosmic variance and inhomogenieties in reionization.

Cosmic DAWN at a Glance

PI(s) James E. Rhoads
Proposal ID 2013B-0528
Years of Observation 2013-2015
Area covered: 3 Deep NEWFIRM fields
Bands J, 1066nm band center – 3.5nm wide (NB)
Median Depth (5σ) 19.9 (J), 19.3 (NB)
Median Seeing 1.3 (J), 1.2 (NB) arcsec
Number of images 6