Discovery of an exceptionally bright giant arc at z = 2.369, gravitationally lensed by the Planck cluster PSZ1 G311.65−18.48 ^⋆⋆

¹ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern, 0315 Oslo, Norway
e-mail: hdahle@astro.uio.no
² Institut d’Astrophysique Spatiale, CNRS, Université Paris-Sud, Université Paris-Saclay, Bât. 121, UMR 8617, 91405 Orsay Cedex, France
³ Sorbonne Universités, UPMC Univ. Paris 06, UMR d’Astrophysique de Paris, 75014 Paris, France
⁴ European Southern Observatory, ESO Vitacura, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile
⁵ Atacama Large Millimeter/submillimeter Array, ALMA Santiago Central Offices, Alonso de Cordova 3107, Vitacura, Casilla 763- 0355, Santiago, Chile
⁶ Université de Toulouse, UPS-Observatoire Midi-Pyrénées, IRAP, 31000 Toulouse, France
⁷ CNRS, Institut de Recherche en Astrophysique et Planétologie (IRAP), 9 avenue Colonel Roche, 31028 Toulouse Cedex 4, France
⁸ Colby College, 5800 Mayflower Hill, Waterville, 04901 Maine, USA
⁹ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA, 02138, USA
¹⁰ Department of Physics, Harvard University, 17 Oxford Street, Cambridge, MA 02138, USA
¹¹ Departemento de Ciencias Fisicas, Universidad Andres Bello, Campus Casona de Las Condes, Fernández Concha 700, Santiago, Chile
¹² Space Research Institute (IKI), Russian Academy of Sciences, Profsoyuznaya Str, 84/32, 117997 Moscow, Russia
¹³ Moscow Institute of Physics and Technology, Dolgoprudny, Institutsky per., 9, 141700 Dolgoprudry, Russia
¹⁴ Kavli Institute for Cosmology Cambridge, Madingley Road, Cambridge, CB3 0HA, UK Institute of Astronomy, Madingley Road, Cambridge, CB3 0HA, UK
¹⁵ Dipartimento di Fisica, Università degli Studi di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy
¹⁶ Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85741 Garching, Germany

Received: 11 February 2016
Accepted: 21 March 2016

Abstract

As part of an all-sky follow-up of the Planck catalogue of Sunyaev-Zeldovich (SZ) cluster candidates detected in the first 14 months of data, we are observing cluster candidates in the southern sky in the optical imaging and spectroscopy through an ESO Large Programme. Inspection of ESO New Technology Telescope (NTT) R-and z-band imaging data from our programme has revealed an unusually large and bright arc in the field of PSZ1 G311.65−18.48. We establish the basic photometric and morphological properties of the arc and provide conclusive evidence for the gravitational lensing nature of this object. Guided by the NTT images, we have obtained a long-slit spectrum with IMACS on the Magellan-I Baade Telescope, covering a part of the arc and the brightest cluster galaxy of PSZ1 G311.65−18.48. Our imaging data confirm the presence of a galaxy cluster coinciding (within 0.́6) with the position of the Planck SZ source. The arc is separated by ~30″ from the brightest cluster galaxy, which closely coincides with the center of curvature of the arc. A photometric analysis yields integrated (Vega) magnitudes of (R,z,J,K_s) = (17.82,17.38,16.75,15.43) for the arc, more than one magnitude brighter than any previously known lensed arc at z ~ 2–3. The arc is a vigorously star-forming galaxy at z = 2.369, while the Planck SZ cluster lens is at z = 0.443.Even when allowing for lensing magnifications as high as μ = 100 still leads to the conclusion that the source galaxy is among the intrinsically most luminous normal (i.e., non-AGN) galaxies known at z ~ 2–3.