Imaging the molecular interstellar medium in a gravitationally lensed star-forming galaxy at z = 5.7^⋆

¹ Departamento de Ciencias Fisicas, Universidad Andres Bello, Fernandez Concha 700, Las Condes, Santiago, Chile
e-mail: yordanka.apostolovski@gmail.com
² Millennium Institute of Astrophysics (MAS), Nuncio Monseñor Sotero Sanz 100, Providencia, Santiago, Chile
³ Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejercito 441, Santiago, Chile
⁴ Department of Astronomy, University of Texas at Austin, 2515 Speedway Stop C1400, Austin, TX 78712, USA
⁵ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
⁶ Aix Marseille Univ., Centre National de la Recherche Scientifique, Laboratoire d’Astrophysique de Marseille, Marseille, France
⁷ Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS B3H 4R2, Canada
⁸ European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching bei München, Germany
⁹ Department of Astronomy and Physics, Saint Mary’s University, Halifax, NS B3H 3C3, Canada
¹⁰ Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
¹¹ Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY 10010, USA
¹² Department of Astronomy, University of Illinois, 1002 West Green St., Urbana, IL 61801, USA
¹³ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
¹⁴ Department of Physics & Astronomy, University of California, Irvine, CA 92697, USA
¹⁵ University of Florida Informatics Institute, 432 Newell Drive, CISE Bldg E251, Gainesville, FL 32611, USA
¹⁶ Cosmic Dawn Center at the Niels Bohr Institute, University of Copenhagen and DTU-Space, Technical University of Denmark, Denmark
¹⁷ Department of Physics, University of Montreal, Pavillon Roger-Gaudry (D-428) 2900 boul. Édouard-Montpetit, Quebec, Canada

Received: 19 February 2019
Accepted: 29 May 2019

Abstract

Aims. We present and study spatially resolved imaging obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) of multiple ¹²CO(J = 6 − 5, 8−7, and 9−8) and two H₂O(2₀₂−1₁₁ and 2₁₁−2₀₂) emission lines and cold dust continuum toward the gravitationally lensed dusty star-forming galaxy SPT 0346-52 at z = 5.656.

Methods. Using a visibility-domain source-plane reconstruction we probe the structure and dynamics of the different components of the interstellar medium (ISM) in this galaxy down to scales of 1 kpc in the source plane.

Results. Measurements of the intrinsic sizes of the different CO emission lines indicate that the higher J transitions trace more compact regions in the galaxy. Similarly, we find smaller dust continuum intrinsic sizes with decreasing wavelength, based on observations at rest frame 130, 300, and 450 μm. The source shows significant velocity structure, and clear asymmetry where an elongated structure is observed in the source plane with significant variations in their reconstructed sizes. This could be attributed to a compact merger or turbulent disk rotation. The differences in velocity structure through the different line tracers, however, hint at the former scenario in agreement with previous [CII] line imaging results. Measurements of the CO line ratios and magnifications yield significant variations as a function of velocity, suggesting that modeling of the ISM using integrated values could be misinterpreted. Modeling of the ISM in SPT 0346-52 based on delensed fluxes indicates a highly dense and warm medium, qualitatively similar to that observed in high-redshift quasar hosts.