2025A&A...701A..85K

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.