Completeness of Lyα detection as a function of Lyα flux in the udf-10 (upper panel) and mosaic (lower panel) fields. The simulated data points and their best-fit completeness functions are indicated by circles and lines, respectively. Black, purple, violet, orange and yellow colors represent redshifts z ≈ 3.3, 4.1, 4.7, 5.3, and 5.9, respectively. Error bars are calculated from the Poisson errors of the numbers of the detected fake emission lines.