(Sub)millimetre interferometric imaging of a sample of COSMOS/AzTEC
  submillimetre galaxies - I. Multiwavelength identifications and redshift
  distribution
  We used the PdBI to map a sample of 15 SMGs in the COSMOS field at the
wavelength of 1.3 mm. The target SMGs were originally discovered in the
JCMT/AzTEC 1.1 mm continuum survey at S/N=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/N>4.5 regardless of multiwavelength counterpart association, and
4<S/N<=4.5 if a multiwavelength counterpart within 1.5" is also present, the
total number of detections in our survey is 22. 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 NIR photometric
redshifts, available spectroscopic redshifts, and redshifts estimated from the
radio-to-submm spectral index we infer a median redshift of
$\tilde{z}=3.20\pm0.25$ 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 AzTEC SMGs detected at 1.1 mm, AzTEC1-15, and studied
previously. This constitutes a complete, flux- and S/N-limited 1.1-mm selected
sample. We find that the median redshift for the 15 brightest AzTEC SMGs
($\tilde{z}=3.05\pm0.44$) 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 $\tilde{z}=3.17\pm0.27$, consistent with
previous results based on mm-selected samples. We further infer that within the
combined AzTEC1-30 sample $\sim25\pm9\%$ of sources separate into multiple
components.
