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Optical and near-infrared properties of submillimetre galaxies Pope, Alexandra

Abstract

We present a new sub-mm 'Super-map' in the HDF-North region, containing 40 statistically robust sources at 850 μm. This map contains new data, and several new sources (including one of the brightest extragalactic sub-mm sources ever detected). We have used ACS HST images and ground-based near-IR observations to study these sources. With the depth achieved by this survey, optical counterparts have been found for all the radio-detected sub-mm sources. We have used the colours, morphologies and photometric redshifts of these secure identifications to help identify counterparts to the radioundetected sub-mm sources, finding that certain combinations of optical properties can be used to successfully identify the counterpart. 74% of our sources have a unique optical counterpart using our new techniques for counterpart identification, and an additional 18% have more than one possibility that meet our criteria in the ACS images. Thus only ~ 8% of our sources lack a plausible optical/near-IR counterpart, meaning that we have the first sample of SCUBA sources which is nearly completely identified in the optical. We have found a much higher ERO rate than other sub-mm surveys, due to the increased depth in the optical images. The median photometric redshift (and quartile range), from optical and near-infrared data, is 1.7 (1.3-2.3) for the radio-detected sub-mm sources, and rises to 2.3 (1.3-2.9) for the radio-undetected sub-sample. We find interesting correlations between the 850 μm flux and both the i775 magnitude, and the photometric redshift. While the quantitative morphologies span a range of values, in general the sub-mm galaxies show larger sizes and a higher degree of asymmetry than other galaxy populations at the same redshifts. We also discuss several improvements in our data analysis procedure, including methods of testing for source reliability.

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