An extended Herschel drop-out source in the center of AS1063: a normal dusty galaxy at z = 6.1 or SZ substructures?

¹ Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse, France
e-mail: frederic.boone@irap.omp.eu
² CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
³ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁴ Centre de Recherche Astrophysique de Lyon, Université Lyon 1, 9 avenue Charles André, 69561 Saint-Genis-Laval, France
⁵ Geneva Observatory, Université de Genève, 51 chemin des Maillettes, 1290 Versoix, Switzerland
⁶ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
⁷ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁸ Department of Physics, Mathematics, and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA
⁹ European Space Astronomy Centre (ESAC)/ESA, Villanueva de la Cañada, 28691 Madrid, Spain
¹⁰ Laboratoire d’astrophysique, École Polytechnique Fédérale de Lausanne, Observatoire de Sauverny, 1290 Versoix, Switzerland
¹¹ Aix-Marseille Université, CNRS, LAM, UMR 7326, 13388 Marseille, France
¹² LERMA, Observatoire de Paris, 61 avenue de l’Observatoire, 75014 Paris, France
¹³ Institute for Computational Cosmology, Department of Physics, Durham University, Durham DH1 3LE, UK
¹⁴ Physics & Astronomy, University of Leicester, Leicester, LE1 7RH, UK
¹⁵ Department of Physics and Atmospheric Science, Dalhousie University Halifax, NS, B3H 3J5, Canada
¹⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁷ Department of Earth and Space Science, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
¹⁸ UPMC Univ Paris 6, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
¹⁹ Departamento de Astrofísica, Facultad de CC. Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
²⁰ Leiden Observatory, Leiden University, PO box 9513, 2300 RA Leiden, The Netherlands

Received: 27 August 2013
Accepted: 2 October 2013

Abstract

In the course of our 870 μm APEX/LABOCA follow-up of the Herschel Lensing Survey we have detected a source in AS1063 (RXC J2248.7-4431) that has no counterparts in any of the Herschel PACS/SPIRE bands, it is a Herschel “drop-out” with S₈₇₀/S₅₀₀ ≥ 0.5. The 870 μm emission is extended and centered on the brightest cluster galaxy, suggesting either a multiply imaged background source or substructure in the Sunyaev-Zel’dovich increment due to inhomogeneities in the hot cluster gas of this merging cluster. We discuss both interpretations with emphasis on the putative lensed source. Based on the observed properties and on our lens model we find that this source may be the first submillimeter galaxy (SMG) with a moderate far-infrared (FIR) luminosity (L_FIR < 10¹²  L_⊙) detected so far at z > 4. In deep HST observations we identified a multiply imaged z ~ 6 source and measured its spectroscopic redshift to be z = 6.107 with VLT/FORS. This source may be associated with the putative SMG, but it is most likely offset spatially by 10−30 kpc and they may be interacting galaxies. With a FIR luminosity in the range [5−15]  × 10¹¹  L_⊙ corresponding to a star formation rate in the range [80−260] M_⊙ yr^-1, this SMG would be more representative of the z > 4 dusty galaxies than the extreme starbursts detected so far. With a total magnification of ~25 it would open a unique window to the normal dusty galaxies at the end of the epoch of reionization.