2016ApJ...829...25H

We present deep number counts at 450 and 850 µm using the SCUBA-2 camera on the James Clerk Maxwell Telescope. We combine data for six lensing cluster fields and three blank fields to measure the counts over a wide flux range at each wavelength. Thanks to the lensing magnification, our measurements extend to fluxes fainter than 1 mJy and 0.2 mJy at 450 µm and 850 µm, respectively. Our combined data highly constrain the faint end of the number counts. Integrating our counts shows that the majority of the extragalactic background light (EBL) at each wavelength is contributed by faint sources with L_IR < 10^12 L_☉, corresponding to luminous infrared galaxies (LIRGs) or normal galaxies. By comparing our result with the 500 µm stacking of K-selected sources from the literature, we conclude that the K-selected LIRGs and normal galaxies still cannot fully account for the EBL that originates from sources with L_IR < 10^12 L_☉. This suggests that many faint submillimeter galaxies may not be included in the UV star formation history. We also explore the submillimeter flux ratio between the two bands for our 450 µm and 850 µm selected sources. At 850 µm, we find a clear relation between the flux ratio and the observed flux. This relation can be explained by a redshift evolution, where galaxies at higher redshifts have higher luminosities and star formation rates. In contrast, at 450 µm, we do not see a clear relation between the flux ratio and the observed flux.