Upper: rest-frame UV LF at z ~ 8 (see Section 5.3). The red circles show the stepwise LF for the WFC3/IR HUDF09+ERS z ~ 8 sample. The red downward arrow shows the 1σ upper limit on the bright end of the LF from our WFC3/IR z ~ 8 search. The black points show the stepwise LF at z ~ 8 derived from the z ~ 8 ERS search. The dashed black line shows the best-fit power-law representation while the red line is for the Schechter fit. The faint-end slope α for the z ~ 7 LF (α = −2.01) is indicated on this figure with the dotted red line. The dotted blue line shows the approximate cutoff observed at the bright end of z ⩽ 7 LFs. The green upper limit (at −22.25 mag) is based upon a recent wide-area z ~ 8 Y-dropout HAWK-I search (Castellano et al. 2010b). See also the caption to Figure 8. Note that the brightest points in our z ~ 8 LF are significantly affected by the three bright sources in the HUDF09-2 field (compare the brightest red point with the black square: based upon the ERS search). Lower: 68% and 95% maximum likelihood contours on the characteristic luminosity M* and the faint-end slope α inferred for the LF at z ~ 8.