the similar (but opposite) systematic effects on luminosities and stellar mass-to-light ratios caused by random photometric redshift errors.

Figure \[fig-stamps\] shows the images of the mass-selected sample at $3.0 \leq z < 4.0$ in the different filters, from the $u$-band to the $24$ $\mu$m [*Spitzer*]{}-MIPS channel.

In order to exclude contamination of the mass-selected sample due to blending, we have also inspected the higher-spatial resolution images available over COSMOS and AEGIS. For COSMOS, we have used the CFHT-WIRCAM $K_{\rm S}$-band image (FWHM$\sim$0.8$^{\prime \prime}$) and the HST-ACS $I_{\rm F814W}$-band images.[^5] For AEGIS, we have used the HST-ACS $I_{\rm F814W}$-band images.[^6] In the HST images, only C1-19536, C1-23152, and A2-15753 are detected, whereas the other sources do not show any obvious detection. All three detected sources appear to be resolved in the ACS images, indicating that the $I$-band fluxes are not dominated by a point-like component. Specifically, C1-19536 and A2-15753 are extended and quite elongated. All the sources but C1-23152 appear very isolated in the ACS images, consistent with the ground-based images. The HST-ACS $I_{\rm F814W}$-band image of C1-23152 reveals two fainter knots at a distance of $\sim1.1^{\prime \prime}$. The two knots contribute about 11% to its total flux in the ACS 