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

Abstract 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 (∼10 10 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 ] λ 3727 up to [N ii ] λ 6583. The ratios of Balmer lines suggest significant dust attenuation ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>E</mml:mi> <mml:msub> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:mi>B</mml:mi> <mml:mo>−</mml:mo> <mml:mi>V</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">gas</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>0.4</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.09</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.10</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> ), 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 H α emission is <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi>SFR(H</mml:mi> <mml:mi>α</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>/</mml:mo> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mspace width="0.25em"/> <mml:msup> <mml:mi>yr</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> <mml:mo>=</mml:mo> <mml:mn>2.0</mml:mn> <mml:msubsup> <mml:mn>2</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.14</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.13</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> , well above the z ∼ 7 star-forming main sequence in terms of specific star formation rate. Strikingly, the ratio of [N ii ] λ 6583/H α emission suggests almost solar metallicity, as does the ratio ([O iii ] λ 5007/H β )/([N ii ] λ 6583/H α ) and the detection of the faint [Fe ii ] λ 4360 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.