The stellar mass density at z ~6 from Spitzer imaging of i'-drop galaxies

We measure the ages, stellar masses, and star formation histories of z ~6 galaxies, observed within 1 Gyr of the big bang. We use imaging from the Hubble Space Telescope (HST) and the Spitzer Space Telescope from the public 'Great Observatories Origins Deep Survey' (GOODS), coupled with ground-based near-infrared imaging, to measure their spectral energy distributions (SEDs) from 0.8–5 μm, spanning the rest-frame ultraviolet (UV) and optical. From our sample of ≈50 'i'-drop' Lyman-break star-forming galaxies in GOODS-South with z'AB 7 could have played a major role in reionizing the Universe