Oral Presentation

ALMA detections of [O III] and [C II] emission lines from A1689-zD1 at z = 7.13

Author(s): Po-Ya Wang (National Tsing Hua University), Yi Hang Wong (National Tsing Hua University), Tetsuya Hashimoto (National Chung Hsing University), Toshinobu Takagi (Japan Space Forum), Tomotsugu Goto (National Tsing Hua University) and NTHU cosmology group

Presenter: Po-Ya Wang (National Tsing Hua University)

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 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. (2021). The observed L[O III]/L[C II] ratio is 2.09 ± 0.09, higher than 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 AGN, shock heating from merging, and starburst. Our moderate-spatial resolution data also reveals that in addition to the observed two clumps shown in previous HST images, there is a redshifted segment to the west of the northern optical clump. Such a structure is consistent with previous claims that A1689-zD1 is a merging galaxy, but with the northern redshifted part being some ejected materials, or that the northern redshifted materials being from a third more highly obscured region of the galaxy.