The AURORA Survey: An Extraordinarily Mature, Star-forming Galaxy at z ∼ 7

We present the properties of a massive, large, dusty, metal-rich, star-forming galaxy at z_spec = 6.73. GOODSN-100182 was observed with JWST/NIRSpec as part of the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) survey, and is also covered by public multiwavelength Hubble Space Telescope and JWST imaging. While the large stellar mass of GOODSN-100182 (∼10¹⁰ M_⊙) was indicated prior to JWST, NIRCam rest-frame optical imaging now reveals the presence of an extended disk (r_eff ∼ 1.5 kpc). In addition, the NIRSpec R ∼ 1000 spectrum of GOODSN-100182 includes the detection of a large suite of rest-frame optical nebular emission lines ranging in wavelength from [O ii] λ3727 up to [N ii] λ6583. The ratios of Balmer lines suggest significant dust attenuation ( E ( B − V ) gas = 0.4 0 − 0.09 + 0.10 ), consistent with the red rest-frame UV slope inferred for GOODSN-100182 (β = −0.50 ± 0.09). The star formation rate based on dust-corrected Hα emission is log ( SFR(H α ) / M ⊙ yr − 1 ) = 2.0 2 − 0.14 + 0.13 , well above the z ∼ 7 star-forming main sequence in terms of specific star formation rate. Strikingly, the ratio of [N ii] λ6583/Hα emission suggests almost solar metallicity, as does the ratio ([O iii] λ5007/Hβ)/([N ii] λ6583/Hα) and the detection of the faint [Fe ii] λ4360 emission feature. Overall, the excitation and ionization properties of GOODSN-100182 more closely resemble those of typical star-forming galaxies at z ∼ 2-3 rather than z ∼ 7. Based on public spectroscopy of the GOODS-N field, we find that GOODSN-100182 resides within a significant galaxy overdensity, and is accompanied by a spectroscopically confirmed neighbor galaxy. GOODSN-100182 demonstrates the existence of mature, chemically enriched galaxies within the first billion years of cosmic time, whose properties must be explained by galaxy formation models.