ALMA Detections of [O iii] and [C ii] Emission Lines From A1689-zD1 at z=7.13

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 mu m and [O iii]88 mu m 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 similar to 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 similar to 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.

Automated summary

The distant galaxy A1689-zD1, discovered through gravitational lensing, offers an important opportunity to study galaxy formation in the early universe. This study detected emission lines and measured redshift, providing insights into the spatial variation and potential physical reasons behind it. The findings shed light on the merging nature of A1689-zD1 and the possibility of obscured regions in the galaxy.