CO, H₂O, H₂O⁺ line and dust emission in a z = 3.63 strongly lensed starburst merger at sub-kiloparsec scales^⋆

¹ European Southern Observatory, Alonso de Córdova 3107, Casilla, 19001 Vitacura, Santiago, Chile
e-mail: cyang@eso.org
² Institut d’Astrophysique de Paris, Sorbonne Université, CNRS, UMR 7095, 98 bis bd Arago, 75014 Paris, France
³ Institut d’Astrophysique Spatiale, CNRS UMR 8617, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay, France
⁴ Purple Mountain Observatory/Key Lab of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210034, PR China
⁵ European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany
⁶ Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK
⁷ Centre for Extragalactic Astronomy, Durham University, Department of Physics, South Road, Durham, DH1 3LE, UK
⁸ National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
⁹ Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
¹⁰ Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, 38406 Saint-Martin-d’Hères, France
¹¹ Department of Physics and Astronomy, University of California, Irvine, CA 92697, USA
¹² School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
¹³ School of Physics and Astronomy, Cardiff University, The Parade, Cardiff CF24 3AA, UK
¹⁴ Department of Physics & Astronomy, University of Iowa, Iowa City, IA 52245, USA
¹⁵ Universidad de Alcalá, Departamento de Física y Matemáticas, Campus Universitario, 28871 Alcalá de Henares, Madrid, Spain
¹⁶ Instituto de Física y Astronomía, Universidad de Valparaíso, Avda. Gran Bretaña 1111, Valparaíso, Chile
¹⁷ Astronomical Observatory Institute, Faculty of Physics, Adam Mickiewicz University, ul. Słoneczna 36, 60-286 Poznań, Poland
¹⁸ Instituto de Astrofísica de Canarias, C/Vía Láctea, s/n, 38205 San Cristóbal de La Laguna, Tenerife, Spain
¹⁹ Universidad de La Laguna, Dpto. Astrofísica, 38206 San Cristóbal de La Laguna, Tenerife, Spain
²⁰ Department of Astronomy, Cornell University, 220 Space Sciences Building, Ithaca, NY 14853, USA
²¹ Leiden Observatory, Leiden University, Post Office Box 9513, 2300 RA Leiden, The Netherlands

Received: 16 July 2018
Accepted: 28 February 2019

Abstract

Using the Atacama Large Millimeter/submillimeter Array (ALMA), we report high angular-resolution observations of the redshift z  = 3.63 galaxy H-ATLAS J083051.0+013224 (G09v1.97), one of the most luminous strongly lensed galaxies discovered by the Herschel-Astrophysical Terahertz Large Area Survey (H-ATLAS). We present 0.″2−0.″4 resolution images of the rest-frame 188 and 419 μm dust continuum and the CO(6–5), H₂O(2₁₁−2₀₂), and J_up = 2 H₂O⁺ line emission. We also report the detection of H₂O(2₁₁−2₀₂) in this source. The dust continuum and molecular gas emission are resolved into a nearly complete ∼1.^″5 diameter Einstein ring plus a weaker image in the center, which is caused by a special dual deflector lensing configuration. The observed line profiles of the CO(6–5), H₂O(2₁₁−2₀₂), and J_up = 2 H₂O⁺ lines are strikingly similar. In the source plane, we reconstruct the dust continuum images and the spectral cubes of the CO, H₂O, and H₂O⁺ line emission at sub-kiloparsec scales. The reconstructed dust emission in the source plane is dominated by a compact disk with an effective radius of 0.7 ± 0.1 kpc plus an overlapping extended disk with a radius twice as large. While the average magnification for the dust continuum is μ ∼ 10−11, the magnification of the line emission varies from 5 to 22 across different velocity components. The line emission of CO(6–5), H₂O(2₁₁−2₀₂), and H₂O⁺ have similar spatial and kinematic distributions. The molecular gas and dust content reveal that G09v1.97 is a gas-rich major merger in its pre-coalescence phase, with a total molecular gas mass of ∼10¹¹ M_⊙. Both of the merging companions are intrinsically ultra-luminous infrared galaxies (ULIRGs) with infrared luminosities L_IR reaching ≳4 × 10¹² L_⊙, and the total L_IR of G09v1.97 is (1.4 ± 0.7)×10¹³ L_⊙. The approaching southern galaxy (dominating from V = −400 to −150 km s⁻¹ relative to the systemic velocity) shows no obvious kinematic structure with a semi-major half-light radius of a_s = 0.4 kpc, while the receding galaxy (0 to 350 km s⁻¹) resembles an a_s = 1.2 kpc rotating disk. The two galaxies are separated by a projected distance of 1.3 kpc, bridged by weak line emission (−150 to 0 km s⁻¹) that is co-spatially located with the cold dust emission peak, suggesting a large amount of cold interstellar medium (ISM) in the interacting region. As one of the most luminous star-forming dusty high-redshift galaxies, G09v1.97 is an exceptional source for understanding the ISM in gas-rich starbursting major merging systems at high redshift.