2022ApJ...929..161W

A1689-zD1 is one of the most distant galaxies, discovered with the aid of gravitational lensing, providing us with an important opportunity to study galaxy formation in the very early universe. In this study, we report the detection of [C II]158 µm and [O III]88 µm emission lines of A1689-zD1 in the Atacama Large Millimeter/submillimeter Array (ALMA) Bands 6 and 8. We measure the redshift of this galaxy as z_sys = 7.133 ± 0.005 based on the [C II] and [O III] emission lines, consistent with that adopted by Bakx et al. The observed L_[O III]_/L[C II]_ ratio is 2.09 ± 0.09, higher than that of most of the local galaxies, but consistent with other z ∼ 7 galaxies. The moderate spatial resolution of ALMA data provided us with a precious opportunity to investigate spatial variation of L_[O III]_/L[C II]_. In contrast to the average value of 2.09, we find a much higher L_[O III]_/L[C II]_ of ∼7 at the center of the galaxy. This spatial variation of L_[O III]_/L[C II]_ was seldom reported for other high-z galaxies. It is also interesting that the peak of the ratio does not overlap with optical peaks. Possible physical reasons include a central active galactic nucleus, shock heating from merging, and a starburst. Our moderate spatial resolution data also reveal that in addition to the observed two clumps shown in previous Hubble Space Telescope images, there is a redshifted segment to the west of the northern optical clump. This structure is consistent with previous claims that A1689-zD1 is a merging galaxy, but with the northern redshifted part being some ejected material, or that the northern redshifted material stems from a third more highly obscured region of the galaxy.