Herschel-ATLAS and ALMA

HATLAS J142935.3-002836, a lensed major merger at redshift 1.027

¹ Universidad de Concepción, Barrio Universitario, Concepción, Chile
² Centro de Astronomia e Astrofísica da Universidade de Lisboa, Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisbon, Portugal
e-mail: hmessias@oal.ul.pt
³ School of Physics and Astronomy, University of Nottingham, NG7 2RD, UK
⁴ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
⁵ Department of Physics & Astronomy, University of California, Irvine, CA 92697, USA
⁶ Universitä Wien, Institut für Astrophysik, Türkenschanzstraß e 17, 1180 Wien, Austria
⁷ Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
⁸ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
⁹ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
¹⁰ European Southern Observatory, Karl Schwarzchild Strasse 2, Garching, Germany
¹¹ INAF, Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, 35122 Padova, Italy
¹² Astronomy Department, California Institute of Technology, MC 249-17, 1200 East California Boulevard, Pasadena, CA 91125, USA
¹³ Department of Astronomy, Cornell University, Ithaca, NY 14853, USA
¹⁴ Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA 19104, USA
¹⁵ The Open University, PO Box 197, Milton Keynes, MK7 6BJ, UK
¹⁶ HH Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK
¹⁷ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹⁸ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹⁹ Astrophysics Group, Imperial College London, Blackett Laboratory, Prince Consort Road, London SW7 2AZ, UK
²⁰ Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, 8140 Christchurch, New Zealand
²¹ School of Physics and Astronomy, Cardiff University, QueensBuildings, The Parade, Cardiff CF24 3AA, UK
²² School of Mathematical Sciences, Queen Mary, University of London, Mile End Road, London, E1 4NS, UK
²³ University of Colorado at Boulder, Center for Astrophysics and Space Astronomy, 389-UCB, Boulder, CO, USA
²⁴ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
²⁵ Infrared Processing and Analysis Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125, USA
²⁶ Institut d’Astrophysique de Paris, UMR 7095, CNRS, UPMC Univ. Paris 06, 98bis boulevard Arago, 75014 Paris, France
²⁷ (SUPA) School of Physics & Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
²⁸ Centre for Astrophysics Research, Science & Technology Research Institute, University of Hertfordshire, Herts AL10 9AB, UK
²⁹ Department of Astronomy and Department of Physics, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA

Received: 16 June 2014
Accepted: 8 July 2014

Abstract

Context. The submillimetre-bright galaxy population is believed to comprise, aside from local galaxies and radio-loud sources, intrinsically active star-forming galaxies, the brightest of which are lensed gravitationally. The latter enable studies at a level of detail beyond what is usually possible by the observation facility.

Aims. This work focuses on one of these lensed systems, HATLAS J142935.3−002836 (H1429−0028), selected in the Herschel-ATLAS field. Gathering a rich, multi-wavelength dataset, we aim to confirm the lensing hypothesis and model the background source’s morphology and dynamics, as well as to provide a full physical characterisation.

Methods. Multi-wavelength high-resolution data is utilised to assess the nature of the system. A lensing-analysis algorithm that simultaneously fits different wavebands is adopted to characterise the lens. The background galaxy dynamical information is studied by reconstructing the 3D source plane of the ALMA CO (J:4 → 3) transition. Near-IR imaging from HST and Keck-AO allows to constrain rest-frame optical photometry independently for the foreground and background systems. Physical parameters (such as stellar and dust masses) are estimated via modelling of the spectral energy distribution taking source blending, foreground obscuration, and differential magnification into account.

Results. The system comprises a foreground edge-on disk galaxy (at z_sp = 0.218) with an almost complete Einstein ring around it. The background source (at z_sp = 1.027) is magnified by a factor of μ ~ 8−10 depending on wavelength. It is comprised of two components and a tens-of-kpc-long tidal tail resembling the Antennæ merger. As a whole, the background source is a massive stellar system (1.32_-0.41^{+ 0.63} × 10¹¹ M_⊙) forming stars at a rate of 394 ± 90  M_⊙ yr^-1, and it has a significant gas reservoir M_ISM = 4.6 ± 1.7 × 10¹⁰ M_⊙. Its depletion time due to star formation alone is thus expected to be τ_SF = M_ISM/ SFR = 117 ± 51 Myr. The dynamical mass of one of the components is estimated to be 5.8 ± 1.7 × 10¹⁰ M_⊙, and, together with the photometric total mass estimate, it implies that H1429−0028 is a major merger system (1:2.8_-1.5^+1.8).