Total F140W magnitude vs. μ. Each galaxy is plotted by a tiny black dot, altogether forming the “galaxy cloud”. The vertical dashed line marks the surface brightness completeness limit at μ_cl ∼ 23.5. Because the galaxy cloud does not exhibit a sharp boundary at this completeness limit, we proceed as follows: The thick red and blue dots mark the average and standard deviation of μ in the total F140W bins (e.g., 18 < F140W < 19 plotted at F140W = 18.5). The solid blue line is a linear fit through the thick blue dots, which are brighter than μ_cl. The intersection of the solid blue line with μ_cl yields a total F140W value ∼24 (horizontal dotted line). At F140W ∼ 24, a large fraction of the galaxy cloud lies right of μ_cl and therefore suffers from surface brightness incompleteness. The total F140W completeness limit (100%) is likely about 1 mag brighter at 23 mag, where the galaxy cloud is brighter than μ_cl.