The AURORA Survey: An Extraordinarily Mature, Star-forming Galaxy at $z\sim 7

• Main Authors: Shapley, Alice E, Sanders, Ryan L, Topping, Michael W, Reddy, Naveen A, Pahl, Anthony J, Oesch, Pascal A, Berg, Danielle A, Bouwens, Rychard J, Brammer, Gabriel, Carnall, Adam C, Cullen, Fergus, Davé, Romeel, Dunlop, James S, Ellis, Richard S, Schreiber, N. M. Förster, Furlanetto, Steven R, Glazebrook, Karl, Illingworth, Garth D, Jones, Tucker, Kriek, Mariska, McLeod, Derek J, McLure, Ross J, Narayanan, Desika, Pettini, Max, Schaerer, Daniel, Stark, Daniel P, Steidel, Charles C, Tang, Mengtao, Clarke, Leonardo, Donnan, Callum T, Kehoe, Emily
• Format: Journal Article
• Language: English
• Published: 30.09.2024
• Subjects: Physics - Astrophysics of Galaxies
• DOI: 10.48550/arxiv.2410.00110

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 AURORA survey, and is also covered by public multi-wavelength HST and JWST imaging. While the large mass of GOODSN-100182 (~10^10 M_sun) was indicated prior to JWST, NIRCam rest-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-optical nebular emission lines ranging in wavelength from [OII]3727 up to [NII]6583. The ratios of Balmer lines suggest significant dust attenuation (E(B-V)_gas=0.40+0.10/-0.09), consistent with the red rest-UV slope inferred for GOODSN-100182 (beta=-0.50+/-0.09). The star-formation rate based on dust-corrected H-alpha emission is log(SFR(H-alpha)/ M_sun/yr)=2.02+0.13/-0.14, well above the z~7 star-forming main sequence in terms of specific SFR. Strikingly, the ratio of [NII]6583/H-alpha emission suggests almost solar metallicity, as does the ratio ([OIII]5007/H-beta)/([NII]6583/H-alpha) and the detection of the faint [FeII]4360 emission feature, whereas the [OIII]5007/[OII]3727 ratio suggests roughly 50% solar metallicity. 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.