Stellar mass vs. UV absolute magnitude M₁₄₀₀ for galaxies at 3.5 <z< 4.5 in the GOODS-South field. The blue solid line is the relation (at 1700 Å rest frame) found by Lee et al. (2012) for LBGs selected with the B − V vs. V − z colour criterion and a S/N in the z₈₅₀ band greater than 6. The red solid line represents the relation as derived by González et al. (2011) at z = 4, for a similar rest-frame wavelength of 1500 Å. The grey triangles show the M/L relation derived by Stark et al. (2013). The dark-green line is the best fit to our own results assuming a constant mass-to-light ratio, or equivalently a slope −0.4 between stellar mass and absolute magnitude. The orange line is the best fit of Duncan et al. (2014). All the relations have been converted to a Salpeter IMF for comparison. Magenta points show galaxies undetected in the deep K-band Hawk-I imaging, while green dots represent objects not detected in 3.6 and 4.5 μm in the Spitzer SEDS imaging.