(Sub)millimetre interferometric imaging of a sample of COSMOS/AzTEC submillimetre galaxies

I. Multiwavelength identifications and redshift distribution^⋆,⋆⋆

¹ Department of PhysicsUniversity of Zagreb, Bijenička cesta 32, 10000 Zagreb, Croatia
e-mail: oskari@phy.hr
² Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
³ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁴ Spitzer Science Center, 314-6 Caltech, Pasadena, CA 91125, USA
⁵ Astronomy Department, Cornell University, 220 Space Sciences Building, Ithaca, NY 14853, USA
⁶ Institut d’Astrophysique de Paris, UMR7095 CNRS, Université Pierre et Marie Curie, 98 bis Boulevard Arago, 75014 Paris, France
⁷ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
⁸ Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, Domaine Universitaire, 38406, Saint Martin d’Hères, France
⁹ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
¹⁰ 23 rue d’Yerres, 91230 Montgeron, France
¹¹ National Optical Astronomy Observatory, 950 North Cherry Avenue, Tucson, AZ 85719, USA
¹² Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching bei München, Germany
¹³ Institute for Astronomy, University of Hawaii, 2680 Woddlawn Drive, Honolulu, HI 96822, USA
¹⁴ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁵ National Radio Astronomy Observatory/NAASC, 520 Edgemont Road, Charlottesville, VA 22903, USA

Received: 19 September 2014
Accepted: 13 February 2015

Abstract

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/N_{1.1 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/N_{1.3 mm}> 4.5 regardless of multiwavelength counterpart association, and 4 <S/N_{1.3 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/N_{1.3 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 $\begin{array}{c}{\mathrm{˜}}_{}\\ \mathit{z}\end{array}$= 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, flux- and S/N-limited 1.1-mm selected sample. We find that the median redshift for the 15 brightest JCMT/AzTEC SMGs ($\begin{array}{c}{\mathrm{˜}}_{}\\ \mathit{z}\end{array}$= 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 $\begin{array}{c}{\mathrm{˜}}_{}\\ \mathit{z}\end{array}$= 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 components.