High resolution spectral imaging of CO(7–6), [CI](2–1), and continuum of three high-z lensed dusty star-forming galaxies using ALMA

¹ Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
e-mail: gayathri.gururajan@lam.fr
² NHFP Hubble Fellow, University of Texas at Austin, 2515 Speedway Stop C1400, Austin, TX, 78712 USA
³ Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
⁴ Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green St., Urbana, IL, 61801 USA
⁵ Center for AstroPhysical Surveys, National Center for Supercomputing Applications, Urbana, IL, 61801 USA
⁶ Department of Physics and Astronomy, University of British Columbia, 6225 Agricultural Road, Vancouver, V6T 1Z1 Canada
⁷ National Research Council, Herzberg Astronomy and Astrophysics, 5071 West Saanich Road, Victoria, V9E 2E7 Canada
⁸ Department of Physics and Atmospheric Science, Dalhousie University, 6310 Coburg Road, B3H 4R2 Halifax, Canada
⁹ European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany
¹⁰ Department of Astronomy, University of Florida, 211 Bryant Space Sciences Center, Gainesville, FL, 32611 USA
¹¹ Center for Computational Astrophysics, Flatiron Institute, 162 Fifth Avenue, New York, NY, 10010 USA
¹² Département de Physique, Université de Montréal, Montreal, Quebec, H3T 1J4 Canada
¹³ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ, 85721 USA
¹⁴ Department of Physics and Astronomy, University of California, Los Angeles, CA, 90095-1547 USA
¹⁵ University of Florida Informatics Institute, 432 Newell Drive, CISE Bldg E251, Gainesville, FL, 32611 USA
¹⁶ Cosmic Dawn Center (DAWN), DTU-Space, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
¹⁷ Department of Physics, University of Illinois Urbana-Champaign, 1110 West Green Street, Urbana, IL, 61801 USA
¹⁸ Max-Planck-Institut für Radioastronomie, Auf dem Hugel 69, 53121 Bonn, Germany

Received: 8 September 2021
Accepted: 15 March 2022

Abstract

High-redshift dusty star-forming galaxies with very high star formation rates (500−3000 M_⊙ yr⁻¹) are key to understanding the formation of the most extreme galaxies in the early Universe. Characterising the gas reservoir of these systems can reveal the driving factor behind the high star formation. Using molecular gas tracers such as, high-J CO lines, neutral carbon lines, and the dust continuum, we can estimate the gas density and radiation field intensity in their interstellar media. In this paper, we present high resolution (∼0.4″) observations of CO(7−6), [CI](2−1), and dust continuum of three lensed galaxies from the South pole telescope – sub-millimetre galaxies (SPT-SMG) sample at z ∼ 3 with the Atacama Large Millimetre/submillimetre Array. Our sources have high intrinsic star formation rates (> 850 M_⊙ yr⁻¹) and rather short depletion timescales (< 100 Myr). Based on the L_[CI](2−1)/L_{CO(7 − 6)} and L_[CI](2−1)/L_IR ratios, our galaxy sample has similar radiation field intensities and gas densities compared to other submillimetre galaxies. We performed visibility-based lens modelling on these objects to reconstruct the kinematics in the source plane. We find that the cold gas masses of the sources are compatible with simple dynamical mass estimates using ULIRG-like values of the CO-H₂ conversion factor α_CO, but not Milky Way-like values. We find diverse source kinematics in our sample: SPT0103−45 and SPT2147−50 are likely rotating disks, while SPT2357−51 is possibly a major merger. The analysis presented in the paper could be extended to a larger sample to determine better statistics of morphologies and interstellar medium properties of high-z dusty star-forming galaxies.