Early galaxy evolution: The complex interstellar medium distribution of the z ∼ 7 galaxy A1689-zD1

¹ Department of Space, Earth and Environment, Chalmers University of Technology, SE-412 96 Gothenburg, Sweden
² Cosmic Dawn Center (DAWN), University of Copenhagen, 2200 Copenhagen N, Denmark
³ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, DK-2200 Copenhagen N, Denmark
⁴ Univ Lyon, Univ Lyon 1, Ens de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, F-69230 Saint-Genis-Laval, France
⁵ Green Bank Observatory, P.O. Box 2 Green Bank, WV, 24944 USA
⁶ Department of Astronomy, The University of Texas at Austin, Austin, TX, 78712 USA
⁷ Tomonaga Center for the History of the Universe (TCHoU), Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, 305-8571 Japan
⁸ Department of Physics, School of Advanced Science and Engineering, Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo, 169-8555 Japan
⁹ Waseda Research Institute for Science and Engineering, Faculty of Science and Engineering, Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo, 169-8555 Japan
¹⁰ National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 Japan
¹¹ Graduate University for Advanced Studies (SOKENDAI), 2-21-1 Osawa, Mitaka, Tokyo, 181-8588 Japan
¹² Astronomical Observatory Institute, Faculty of Physics and Astronomy, Adam Mickiewicz University, Poznań, Poland

^⋆ Corresponding author: kirsten.knudsen@chalmers.se

Received: 29 November 2024
Accepted: 30 June 2025

Abstract

We observed the gravitationally lensed (μ = 9.6 ± 0.19) galaxy A1689-zD1 at z = 7.1 in bands 3, 6, and 8 of the Atacama Large Millimeter/submillimeter Array. These high-resolution observations (≈200 pc) enabled us to separate the source into five components in the [C II] 158 μm and [O III] 88 μm emission lines within a projected distance of 2 kpc. Even though these components appear to vary strongly from one another in both their line, continuum, and optical characteristics, the assembly of components do not show ordered rotation and appear consistent with simulations of a galaxy system undergoing the process of assembly. The total dynamical mass of the galaxy (2 × 10¹⁰ M_⊙) is an order of magnitude larger than the spectrally estimated stellar mass, suggesting a near-complete optical obscuration of the bulk of the stellar component. Comparing the line ratios as well as the line properties to other properties such as the star formation rate, we find that A1689-zD1 is consistent with the relations derived from local star-forming galaxies. Even though A1689-zD1 lies on local star formation scaling relations and has a high dust and stellar mass estimate, the kinematics suggest it is in an early assembly stage, which could lead to it becoming a disk galaxy at a later stage.