We investigate the properties of 1088 Lyman Break Galaxies ( LBGs ) at z \sim 3 selected from a \sim 2.63 deg ^ { 2 } sub-region of the First Look Survey field using the ground-based multi-color data and the Spitzer Space Telescope mid-infrared data at 3–8 and 24 \mu m. With the wide area and the broad wavelength coverage , we sample a large number of ‘ ‘ rare ’ ’ u -band dropouts which are massive ( M _ { * } > 10 ^ { 11 } M _ { \odot } ) , allowing us to perform a statistical analysis of these subsets of LBGs that have not been studied in detail .
Optically bright ( R _ { AB } \leq 24.5 mag ) LBGs detected in mid-infrared ( S _ { 3.6 \mu m } \geq 6 \mu Jy ) reside at the most massive and dusty end of the LBG population , with relatively high and tight M / L in rest-frame near-infrared .
Most infrared-luminous LBGs ( S _ { 24 \mu m } \geq 100 \mu Jy ) are dusty star-forming galaxies with star formation rates of 100–1000 M _ { \odot } /yr , total infrared luminosity of > 10 ^ { 12 } L _ { \odot } .
By constructing the UV luminosity function of massive LBGs , we estimate that the lower limit for the star formation rate density from LBGs more massive than 10 ^ { 11 } M _ { \odot } at z \sim 3 is \geq 3.3 \times 10 ^ { -3 } M _ { \odot } / yr / Mpc ^ { 3 } , showing for the first time that the UV-bright population of massive galaxies alone contributes significantly to the global star formation rate density at z \sim 3 .
When combined with the star formation rate densities at z < 2 , our result reveals a steady increase in the contribution of massive galaxies to the global star formation from z = 0 to z \sim 3 , providing strong support to the downsizing of galaxy formation .