LYMAN BREAK GALAXIES AT z ≈ 1.8-2.8: GALEX/NUV IMAGING OF THE SUBARU DEEP FIELD

A photometric sample of similar to 8000 V < 25.3 candidate Lyman break galaxies (LBGs) has been selected by combining Subaru/Suprime-Cam BVR(C)i'z' optical data with deep GALEX/NUV imaging of the Subaru Deep Field. Follow-up spectroscopy confirmed 24 LBGs at 1.5 less than or similar to z less than or similar to 2.7. Among the optical spectra, 12 have Lya emission with rest-frame equivalent widths of approximate to 5-60 angstrom. The success rate for identifying LBGs as NUV-dropouts at 1.5 < z < 2.7 is 86%. The rest-frame UV (1700 angstrom) luminosity function (LF) is constructed from the photometric sample with corrections for stellar contamination and z < 1.5 interlopers (lower limits). The LF is 1.7 +/- 0.1 (1.4 +/- 0.1 with a hard upper limit on stellar contamination) times higher than those of z similar to 2 BXs and z similar to 3 LBGs. Three explanations were considered, and it is argued that significantly underestimating low-z contamination or effective comoving volume is unlikely: the former would be inconsistent with the spectroscopic sample at 93% confidence, and the second explanation would not resolve the discrepancy. The third scenario is that different photometric selection of the samples yields nonidentical galaxy populations, such that some BX galaxies are LBGs and vice versa. This argument is supported by a higher surface density of LBGs at all magnitudes while the redshift distribution of the two populations is nearly identical. This study, when combined with other star formation rate (SFR) density UV measurements from LBG surveys, indicates that there is a rise in the SFR density: a factor of 3-6 (3-10) increase from z similar to 5 (z similar to 6) to z similar to 2, followed by a decrease to z similar to 0. This result, along with past sub-mm studies that find a peak at z similar to 2 in their redshift distribution, suggests that z similar to 2 is the epoch of peak star formation.