2013ApJ...762...81C

We present the results of SCUBA-2 observations at 450 µm and 850 µm of the field lensed by the massive cluster A370. With a total survey area >100 arcmin² and 1σ sensitivities of 3.92 and 0.82 mJy/beam at 450 and 850 µm, respectively, we find a secure sample of 20 sources at 450 µm and 26 sources at 850 µm with a signal-to-noise ratio (S/N) > 4. Using the latest lensing model of A370 and Monte Carlo simulations, we derive the number counts at both wavelengths. The 450 µm number counts probe a factor of four deeper than the counts recently obtained from the Herschel Space Telescope at similar wavelengths, and we estimate that ∼47%-61% of the 450 µm extragalactic background light resolved into individual sources with 450 µm fluxes greater than 4.5 mJy. The faint 450 µm sources in the 4σ sample have positional accuracies of 3 arcsec, while brighter sources (S/N >6σ) are good to 1.4 arcsec. Using a deep radio map (1σ ∼ 6 µJy) we find that the percentage of submillimeter sources having secure radio counterparts is 85% for 450 µm sources with intrinsic fluxes >6 mJy and 67% for 850 µm sources with intrinsic fluxes >4 mJy. We also find that 67% of the >4σ 450 µm sources are detected at 850 µm, while the recovery rate at 450 µm of >4σ 850 µm sources is 54%. Combined with the source redshifts estimated using millimetric flux ratios, the recovered rate is consistent with the scenario where both 450 µm and 20 cm emission preferentially select lower redshift dusty sources, while 850 µm emission traces a higher fraction of dusty sources at higher redshifts. We identify potential counterparts in various wavelengths from X-ray to mid-infrared and measure the multiwavelength photometry, which we then use to analyze the characteristics of the sources. We find three X-ray counterparts to our robust submillimeter sample (S/N > 5), giving an active galactic nucleus fraction for our 450 (850) µm sample of 3/8 (3/9) or 38% (33%). We also find a correlation between the K_s band and the 850 µm/20 cm flux ratio.