An ALMA survey of submillimeter galaxies in the COSMOS field: Multiwavelength counterparts and redshift distribution

¹ Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, 1058 Santiago, Chile
e-mail: drew.brisbin@mail.udp.cl
² Department of Physics, Faculty of Science, University of Zagreb, Bijenička cesta 32, 10000 Zagreb, Croatia
³ CAS Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Nandan Road 80, 200030 Shanghai, PR China
⁴ Chinese Academy of Sciences South America Center for Astronomy, 7591245 Santiago, Chile
⁵ Argelander-Institut für Astronomie, Universität of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁶ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretana 1111, Valparaíso, Chile
⁷ Laboratoire AIM, IRFU/Service d’Astrophysique – CEA/DSM – CNRS – Université Paris Diderot, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
⁸ Aix Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille), UMR 7326, 13388 Marseille, France
⁹ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
¹⁰ Department of Astronomy, California Institute of Technology, MC 249-17, 1200 East California Blvd, Pasadena, CA 91125, USA
¹¹ Department of Astronomy, The University of Texas at Austin, 2515 Speedway Blvd Stop C1400, Austin, TX 78712, USA
¹² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹³ Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
¹⁴ Department of Physics and Astronomy, Clemson University, Kinard Lab of Physics, Clemson, SC 29634-0978, USA
¹⁵ Sorbonne Universités, UPMC Univ Paris 06, UMR 7095, Institut d’Astrophysique de Paris, 75005 Paris, France
¹⁶ Astronomy Department, Cornell University, 220 Space Sciences Building, Ithaca, NY 14853, USA
¹⁷ Instituto de Astrofísica, Universidad Católica de Chile, Av. Vicuna Mackenna 4860, 782-0436 Macul, Santiago, Chile
¹⁸ Centro de Astro-Ingeniería, Universidad Católica de Chile, Av. Vicuna Mackenna 4860, 782-0436 Macul, Santiago, Chile
¹⁹ Max-Planck-Institut für Extraterrestrische Physik (MPE), Postfach 1312, 85741 Garching, Germany
²⁰ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
²¹ Max-Planck-Institut für Astronomie, Königstuhl, 17, 69117 Heidelberg, Germany
²² NASA Headquarters, 300 E. St SW, Washington, DC 20546, USA

Received: 3 February 2017
Accepted: 21 August 2017

Abstract

We carried out targeted ALMA observations of 129 fields in the COSMOS region at 1.25 mm, detecting 152 galaxies at S/N ≥ 5 with an average continuum RMS of 150 μJy. These fields represent a S/N-limited sample of AzTEC/ASTE sources with 1.1 mm S/N ≥ 4 over an area of 0.72 square degrees. Given ALMA’s fine resolution and the exceptional spectroscopic and multiwavelength photometric data available in COSMOS, this survey allows us unprecedented power in identifying submillimeter galaxy counterparts and determining their redshifts through spectroscopic or photometric means. In addition to 30 sources with prior spectroscopic redshifts, we identified redshifts for 113 galaxies through photometric methods and an additional nine sources with lower limits, which allowed a statistically robust determination of the redshift distribution. We have resolved 33 AzTEC sources into multi-component systems and our redshifts suggest that nine are likely to be physically associated. Our overall redshift distribution peaks at z ~ 2.0 with a high-redshift tail skewing the median redshift to .48 ± 0.05. We find that brighter millimeter sources are preferentially found at higher redshifts. Our faintestsources, with S_{1.25 mm} < 1.25 mJy, have a median redshift of .18 ± 0.09, while the brightest sources, S_{1.25 mm} > 1.8 mJy, have a median redshift of .08 ± 0.17. After accounting for spectral energy distribution shape and selection effects, these results are consistent with several previous submillimeter galaxy surveys, and moreover, support the conclusion that the submillimeter galaxy redshift distribution is sensitive to survey depth.