Deep 1.1 mm-wavelength imaging of the GOODS-S field by AzTEC/ASTE - I. Source catalogue and number counts

We present the first results from a 1.1mm confusion-limited map of the Great Observatories Origins Deep Survey-South (GOODS-S) taken with the AzTEC camera on the Atacama Submillimeter Telescope Experiment. We imaged a 270 arcmin(2) field to a 1 sigma depth of 0.48-0.73 mJy beam(-1), making this one of the deepest blank-field surveys at mm-wavelengths ever achieved. Although by traditional standards our GOODS-S map is extremely confused due to a sea of faint underlying sources, we demonstrate through simulations that our source identification and number counts analyses are robust, and the techniques discussed in this paper are relevant for other deeply confused surveys. We find a total of 41 dusty starburst galaxies with signal-to-noise ratios S/N >= 3.5 within this uniformly covered region, where only two are expected to be false detections, and an additional seven robust source candidates located in the noisier (1 sigma approximate to 1 mJy beam(-1)) outer region of the map. We derive the 1.1mm number counts from this field using two different methods: a fluctuation or P(d) analysis and a semi-Bayesian technique and find that both methods give consistent results. Our data are well fit by a Schechter function model with (S', N3 mJy, alpha) = (1.30(-0.25)(+0.19) mJy, 160(-28)(+27) mJy(-1) deg(-2), -2.0). Given the depth of this survey, we put the first tight constraints on the 1.1mm number counts at S-1.1mm = 0.5 mJy, and we find evidence that the faint end of the number counts at S-850 mu m less than or similar to 2.0mJy from various SCUBA surveys towards lensing clusters are biased high. In contrast to the 870 mu m survey of this field with the LABOCA camera, we find no apparent underdensity of sources compared to previous surveys at 1.1 mm; the estimates of the number counts of SMGs at flux densities >1mJy determined here are consistent with those measured from the AzTEC/SHADES survey. Additionally, we find a significant number of SMGs not identified in the LABOCA catalogue. We find that in contrast to observations at lambda = 500 mu m, MIPS 24 mu m sources do not resolve the total energy density in the cosmic infrared background at 1.1mm, demonstrating that a population of z greater than or similar to 3 dust-obscured galaxies that are unaccounted for at these shorter wavelengths potentially contribute to a large fraction (similar to 2/3) of the infrared background at 1.1mm.