Mean UV slope as a function of redshifts for L ≳ L^* galaxies from this work and from the literature. Estimates from Finkelstein et al. (2012) are for the L >  0.75L^* range (Table 4 in their paper), while points from Bouwens et al. (2012b) are for objects with average M_UV = −20.5 up to z = 6, and M_UV = −20.25 at z = 7 (Table 4 in their paper). Filled and open symbols for this work and Castellano et al. (2012) indicate the Gaussian and the log-normal best-fit values, respectively. The median β values from Hathi et al. (2013) based on UV slope fits in the rest-frame 1300–1900 Å and 1300–3400 Å wavelength ranges are indicated as filled and open squares, respectively. Error bars for all the points indicate the 1σ uncertainty on the mean, except for the Bouwens et al. (2009, 2012b)z = 4 − 5 values, for which they are representative of the 1σ scatter.