A solar metallicity galaxy at z > 7? Possible detection of the [N II] 122 μm and [O III] 52 μm lines
Abstract
We present the first detection of the [N II] 122 μm and [O III] 52 μm lines for a reionisation-epoch galaxy. Based on these lines and previous [C II] 158 μm and [O III] 88 μm measurements, using two different radiative transfer models of the interstellar medium, we estimate an upper limit on electron density of 500 cm-3 and a gas-phase metallicity Z/Z 1.1 0.2 for A1689-zD1, a gravitationally-lensed, dusty galaxy at z = 7.133. Other measurements or indicators of metallicity so far in galaxy interstellar media at z 6 are typically an order of magnitude lower than this. The unusually high metallicity makes A1689-zD1 inconsistent with the fundamental metallicity relation, although there is likely significant dust obscuration of the stellar mass, which may partly resolve the inconsistency. Given a solar metallicity, the dust-to-metals ratio is a factor of several lower than expected, hinting that galaxies beyond z 7 may have lower dust formation efficiency. Finally, the inferred nitrogen enrichment compared to oxygen, on which the metallicity measurement depends, indicates that star-formation in the system is older than about 250 Myr, pushing the beginnings of this galaxy to z > 10.
Turn this paper into a full lesson
ArcXiv compiles a staged curriculum from this paper: 8-12 lessons across beginner → advanced, synthesised section guides, visuals, flashcards, a quiz, exercises, and on-demand deep dives per section. Grounded in the abstract, never invented.