We combined deep U -band imaging from the KPNO-4m/MOSAIC camera with very deep multi-waveband imaging data from optical to near-infrared wavelengths , to select Lyman Break Galaxies ( LBGs ) at z \sim 3 using U - V and V - R _ { c } colors in the Subaru Deep Field . With the resulting sample of 5161 LBGs , we construct the UV luminosity function down to M _ { \mathrm { UV } } = -18 and find a steep faint-end slope of \alpha = -1.78 \pm 0.05 . We analyze rest-frame UV-to-NIR spectral energy distributions ( SEDs ) generated from the median optical photometry and photometry on median-composite IR images ( formed from stacks around the optical positions of LBGs ) . In the stacks of faint LBGs , we find a systematic background depression centered on the position of the galaxy . A series of experiments confirmed our view that this deficit results from the systematic difficulty of SExtractor ( or any other object-finding routine ) in finding faint galaxies in regions with higher-than-average surface densities of foreground galaxies . We corrected our stacked magnitudes for this effect and suggest that other stacking studies should also make such corrections . Best-fit stellar population templates for the stacked LBG SEDs indicate stellar masses and star-formation rates ( SFRs ) of \log _ { 10 } ( M _ { * } / { M } _ { \odot } ) \simeq 10 and \simeq 50 M _ { \odot } yr ^ { -1 } at \langle i ^ { \prime } _ { \mathrm { AB } } \rangle = 24 , down to \log _ { 10 } ( M _ { * } / { M } _ { \odot } ) \simeq 8 and \simeq 3 M _ { \odot } yr ^ { -1 } at \langle i ^ { \prime } _ { \mathrm { AB } } \rangle = 27 . For the faint stacked LBGs there is a \sim 1 magnitude excess over the expected stellar continuum in the K -band . We interpret this excess flux as emission from the redshifted gaseous [ OIII ] \lambda \lambda 4959 , 5007 and H \beta lines . The observed excesses imply equivalent widths that increase with decreasing mass , reaching { EW _ { 0 } ( [ OIII ] 4959 , 5007 + H \beta ) } \gtrsim 1500 Å ( rest-frame ) in the faintest bin . Such strong [ OIII ] emission is seen only in a miniscule fraction of the most extreme local emission-line galaxies , but it probably universal in the faint galaxies that reionized the universe . This finding has strong implications for finding and studying the most common galaxies at high redshifts with upcoming surveys . Finally , we analyze clustering by computing the angular correlation function and performing halo occupation distribution ( HOD ) analysis . We find a mean dark halo mass of \log _ { 10 } ( \langle M _ { { h } } \rangle / h ^ { -1 } M _ { \odot } ) = 11.29 \pm 0.12 for the full sample of LBGs , and \log _ { 10 } ( \langle M _ { { h } } \rangle / h ^ { -1 } M _ { \odot } ) = 11.49 \pm 0.1 for the brightest half of the sample . The results support the notion that more massive dark matter halos host more luminous LBGs .