Planck’s dusty GEMS: The brightest gravitationally lensed galaxies discovered with the Planck all-sky survey^⋆

¹ Institut d’Astrophysique Spatiale, UMR 8617, Université Paris-Sud, Bât. 121, 91405 Orsay, France
² CNRS, 91405 Orsay, France
³ Institut Universitaire de France, Paris, France
⁴ Department of Physics & Astronomy, University of British 66 Columbia, 6224 Agricultural Road, Vancouver, British Columbia, 58 Canada
⁵ Institut de Radio Astronomie Millimétrique (IRAM), 300 rue de la Piscine, Domaine Universitaire, 38406 Saint-Martin d’Hères, France
⁶ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
⁷ Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
⁸ Université de Toulouse, UMS-OMP, IRAP, 31028 Toulouse Cedex 4, France
⁹ CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028 Toulouse Cedex 4, France
¹⁰ INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
¹¹ CEA-Saclay, 91191 Gif-sur-Yvette, France
¹² Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
¹³ ESAC, ESA, PO Box 78, Villanueva de la Cañada, 28691 Madrid, Spain
¹⁴ Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125, USA
¹⁵ European Southern Observatory, Karl-Schwarzschild Str. 2, 85748 Garching, Germany
¹⁶ European Southern Observatory, ESO Vitacura, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile
¹⁷ Atacama Large Millimeter/submillimeter Array, ALMA Santiago Central Offices, Alonso de Cordova 3107, Vitacura, Casilla 763-0355, Santiago, Chile
¹⁸ School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
¹⁹ UPMC Univ. Paris 06, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
²⁰ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK

Received: 8 October 2014
Accepted: 5 June 2015

Abstract

We present an analysis of CO spectroscopy and infrared-to-millimetre dust photometry of 11 exceptionally bright far-infrared (FIR) and sub-mm sources discovered through a combination of the Planck all-sky survey and follow-up Herschel-SPIRE imaging – “Planck’s Dusty Gravitationally Enhanced subMillimetre Sources”. Each source has a secure spectroscopic redshift z = 2.2–3.6 from multiple lines obtained through a blind redshift search with EMIR at the IRAM 30-m telescope. Interferometry was obtained at IRAM and the SMA, and along with optical/near-infrared imaging obtained at the CFHT and the VLT reveal morphologies consistent with strongly gravitationally lensed sources, including several giant arcs. Additional photometry was obtained with JCMT/SCUBA-2 and IRAM/GISMO at 850 μm and 2 mm, respectively. The SEDs of our sources peak near either the 350 μm or 500 μm bands of SPIRE with peak flux densities between 0.35 and 1.14 Jy. All objects are extremely bright isolated point sources in the 18′′ beam of SPIREat 250 μm, with apparent FIR luminosities of up to 3 × 10¹⁴ L_⊙ (not correcting for the lensing effect). Their morphologies, sizes, CO line widths, CO luminosities, dust temperatures, and FIR luminosities provide additional empirical evidence that these are amongst the brightest strongly gravitationally lensed high-redshift galaxies on the sub-mm sky. Our programme extends the successful wide-area searches for strongly gravitationally lensed high-redshift galaxies (carried out with the South Pole Telescope and Herschel) towards even brighter sources, which are so rare that their systematic identification requires a genuine all-sky survey like Planck. Six sources are above the ≃600 mJy 90% completeness limit of the Planck catalogue of compact sources (PCCS) at 545 and 857 GHz, which implies that these must literally be amongst the brightest high-redshift FIR and sub-mm sources on the extragalactic sky. We discuss their dust masses and temperatures, and use additional WISE 22-μm photometry and template fitting to rule out a significant contribution of AGN heating to the total infrared luminosity. Six sources are detected in FIRST at 1.4 GHz, and the others have sensitive upper limits. Four have flux densities brighter than expected from the local FIR-radio correlation, but in the range previously found for high-z sub-mm galaxies, one has a deficit of FIR emission, and 6 are consistent with the local correlation, although this includes 3 galaxies with upper limits. We attribute this to the turbulent interstellar medium of these galaxies, rather than the presence of radio AGN. The global dust-to-gas ratios and star-formation efficiencies of our sources are predominantly in the range expected from massive, metal-rich, intense, high-redshift starbursts. An extensive multi-wavelength follow-up programme is being carried out to further characterize these sources and the intense star formation within them.