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arXiv · 2211.01424

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

Meghana Killi·Darach Watson·Seiji Fujimoto·Hollis Akins·Kirsten Knudsen·Johan Richard·Yuichi Harikane·Dimitra Rigopoulou·Francesca Rizzo·Michele Ginolfi·Gergö Popping·Vasily Kokorev
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Abstract

We present the first detection of the [N II] 122 $μ$m and [O III] 52 $μ$m lines for a reionisation-epoch galaxy. Based on these lines and previous [C II] 158 $μ$m and [O III] 88 $μ$m measurements, using two different radiative transfer models of the interstellar medium, we estimate an upper limit on electron density of $\lesssim$ 500 cm$^{-3}$ and a gas-phase metallicity $Z/Z_\odot \sim 1.1 \pm 0.2$ 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 $z \gtrsim$ 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 $z \sim$ 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.

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Meghana Killi, Darach Watson, Seiji Fujimoto, Hollis Akins, Kirsten Knudsen, Johan Richard, Yuichi Harikane, Dimitra Rigopoulou, Francesca Rizzo, Michele Ginolfi, Gergö Popping, Vasily Kokorev. 2023-03-08. A solar metallicity galaxy at $z >$ 7? Possible detection of the [N II] 122 $μ$m and [O III] 52 $μ$m lines. https://doi.org/10.1093/mnras%2Fstad687

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