paper

A solar metallicity galaxy at 7? Possible detection of the [N II] 122 m and [O III] 52 m lines

arXiv:2211.01424 · doi:10.1093/mnras/stad687

Abstract

We present the first detection of the [N II] 122 m and [O III] 52 m lines for a reionisation-epoch galaxy. Based on these lines and previous [C II] 158 m and [O III] 88 m measurements, using two different radiative transfer models of the interstellar medium, we estimate an upper limit on electron density of 500 cm and a gas-phase metallicity for A1689-zD1, a gravitationally-lensed, dusty galaxy at = 7.133. Other measurements or indicators of metallicity so far in galaxy interstellar media at 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 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 10.

10 pages, 7 figures; Published MNRAS: 06 March 2023

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