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arXiv · 2202.09945

Detection of nitrogen and oxygen in a galaxy at the end of reionization

Ken-ichi Tadaki·Akiyoshi Tsujita·Yoichi Tamura·Kotaro Kohno·Bunyo Hatsukade·Daisuke Iono·Minju M. Lee·Yuichi Matsuda·Tomonari Michiyama·Tohru Nagao·Kouichiro Nakanishi·Yuri Nishimura·Toshiki Saito·Hideki Umehata·Jorge Zavala
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Abstract

We present observations of [NII] 205 $μ$m, [OIII] 88 $μ$m and dust emission in a strongly-lensed, submillimeter galaxy (SMG) at $z=6.0$, G09.83808, with the Atacama Large Millimeter/submillimeter Array (ALMA). Both [NII] and [OIII] line emissions are detected at $>12σ$ in the 0.8$"$-resolution maps. Lens modeling indicates that the spatial distribution of the dust continuum emission is well characterized by a compact disk with an effective radius of 0.64$\pm$0.02 kpc and a high infrared surface brightness of $Σ_\mathrm{IR}=(1.8\pm0.3)\times10^{12}~L_\odot$ kpc$^{-2}$. This result supports that G09.83808 is the progenitors of compact quiescent galaxies at $z\sim4$, where the majority of its stars are expected to be formed through a strong and short burst of star formation. G09.83808 and other lensed SMGs show a decreasing trend of the [NII] line to infrared luminosity ratio with increasing continuum flux density ratio between 63 $μ$m and 158 $μ$m, as seen in local luminous infrared galaxies (LIRGs). The decreasing trend can be reproduced by photoionization models with increasing ionization parameters. Furthermore, by combining the [NII]/[OIII] luminosity ratio with far-infrared continuum flux density ratio in G09.83808, we infer that the gas phase metallicity is already $Z\approx 0.5-0.7~Z_\odot$. G09.83808 is likely one of the earliest galaxies that has been chemically enriched at the end of reionization.

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Ken-ichi Tadaki, Akiyoshi Tsujita, Yoichi Tamura, Kotaro Kohno, Bunyo Hatsukade, Daisuke Iono, Minju M. Lee, Yuichi Matsuda, Tomonari Michiyama, Tohru Nagao, Kouichiro Nakanishi, Yuri Nishimura, Toshiki Saito, Hideki Umehata, Jorge Zavala. 2022-02-21. Detection of nitrogen and oxygen in a galaxy at the end of reionization. https://doi.org/10.1093/pasj%2Fpsac018

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