A spectroscopic measure of the star formation rate density in dwarf galaxies at z ~ 1

We use a K-selected (22.5 < K-AB < 24.0) sample of dwarf galaxies (8.4 < log(M-*/M-circle dot) < 10) at 0.89 < z < 1.15 in the Chandra Deep Field-South to measure their contribution to the global star formation rate density (SFRD), as inferred from their [O II] flux. By comparing with [O II]-based studies of higher stellar mass galaxies, we robustly measure a turnover in the [O II] luminosity density at a stellar mass of M similar to 10(10) M-circle dot. By comparison with the [O II]-based SFRD measured from the Sloan Digital Sky Survey we confirm that, while the SFRD of the lowest mass galaxies changes very little with time, the SFRD of more massive galaxies evolves strongly, such that they dominate the SFRD at z = 1.