(Sub)millimetre interferometric imaging of a sample of COSMOS/AzTEC submillimetre galaxies – I. Multiwavelength identifications and redshift distribution

We used the Plateau de Bure Interferometer (PdBI) to map a sample of 15 submillimetre galaxies (SMGs) in the COSMOS field at the wavelength of 1.3 mm. The target SMGs were originally discovered in the James Clerk Maxwell Telescope (JCMT)/AzTEC 1.1 mm continuum survey at S/N1.1 mm = 4 − 4.5. This paper presents, for the first time, interferometric millimetre-wavelength observations of these sources. The angular resolution of our observations, ∼ 1′′ .8, allowed us to accurately determine the positions of the target SMGs. Using a detection threshold of S/N1.3 mm > 4.5 regardless of multiwavelength counterpart association, and 4 < S/N1.3 mm ≤ 4.5 if a multiwavelength counterpart within 1′′ .5 is also present, the total number of detections in our survey is 22. The most significant PdBI detection of S/N1.3 mm = 10.3 is towards AzTEC19. Three of our detected SMGs (AzTEC21, 27, and 28; which corresponds to 20%) are marginally resolved at our angular resolution, and these sources are found to have elongated or clumpy morphologies and/or multiple components. Using optical to near-infrared photometric redshifts, available spectroscopic redshifts, and redshifts estimated from the radio-to-submm spectral index we infer a median redshift of z̃ = 3.20± 0.25 for our sample. To study the overall multiplicity and redshift distribution of flux-limited samples of SMGs we combined these sources with the 15 brightest JCMT/AzTEC SMGs detected at 1.1 mm, AzTEC1–15, and studied previously. This constitutes a complete, fluxand S/N-limited 1.1-mm selected sample. We find that the median redshift for the 15 brightest JCMT/AzTEC SMGs (z̃ = 3.05 ± 0.44) is consistent with that for AzTEC16–30. This conforms to recent observational findings that SMGs do not exhibit any significant trend between the redshift and (sub)mm flux density. For the combined AzTEC1–30 sample we derive a median redshift of z̃ = 3.17 ± 0.27, consistent with previous results based on mm-selected samples. We further infer that within the combined AzTEC1–30 sample ∼ 25 ± 9% of sources separate into multiple