The first blind H-alpha narrow-band survey of star-formation at z>6

We propose to use NIRCam's narrow-band filters to observe a 65 sq. arcmin mosaic in the well-studied COSMOS-CANDELS field, to identify and study ~1000 emission-line selected galaxies across cosmic time. Our primary science driver is the detection of ~40 H-alpha emitters at redshift z>6, using difference imaging between the closely-spaced F466N and F470N filters. The H-alpha emission line is the best-calibrated star-formation indicator in the nearby Universe, and narrow-band surveys have mapped the evolution of H-alpha emitters out to the peak star-formation epoch at z~2. At higher redshift, samples of star-forming galaxies and estimates of the cosmic star-formation rate density are almost ubiquitously based on rest-frame UV observations; this single approach carries a high risk of systematic effects, both in the populations of galaxies selected and in their derived properties. Our proposal will provide the first critical test of this, producing a clean, emission-line selected sample of galaxies in to the Epoch of Reionisation, whose properties will be characterised and compared against UV-selected samples. Simultaneous imaging with the F212N and F200W filters will detect ~200 faint H-alpha emitters at cosmic noon, z~2, probing a factor 5 deeper than any previous study. Using NIRCam's remarkable angular resolution we will measure the ionised gas structures of these galaxies (and hundreds of other line-emitters at z>1.5, including ~10 [OIII] emitters at z=8.3) at sub-kpc resolution and determine how the relationship between UV and ionised gas structures varies with host galaxy properties, in order to delineate the physical processes driving star formation at these reshifts.