The AURORA Survey: A New Era of Emission-line Diagrams with JWST/NIRSpec
Alice E. Shapley, Ryan L. Sanders, Michael W. Topping, Naveen A. Reddy, Danielle A. Berg, R. J. Bouwens, Gabriel Brammer, Adam C. Carnall, Fergus Cullen, Romeel Davé, J. S. Dunlop, Richard S. Ellis, N. M. Förster Schreiber, Steven R. Furlanetto, Karl Glazebrook, G. D. Illingworth, Tucker Jones, Mariska Kriek, D J McLeod, R. J. McLure, Desika Narayanan, Pascal A. Oesch, Anthony J. Pahl, Max Pettini, D. Schaerer, Daniel P. Stark, Charles C. Steidel, Mengtao Tang, L. Clarke, Callum T. Donnan, Emily Kehoe
Abstract
Abstract We present results on the emission-line properties of z = 1.4–7.5 star-forming galaxies in the Assembly of Ultradeep Rest-optical Observations Revealing Astrophysics (AURORA) Cycle 1 JWST/NIRSpec program. Based on its depth, continuous wavelength coverage from 1 to 5 μ m, and medium spectral resolution ( R ∼ 1000), AURORA includes detections of a large suite of nebular emission lines spanning a broad range in rest-frame wavelength. We investigate the locations of AURORA galaxies in multiple different emission-line diagrams, including traditional BPT diagrams of [O iii ] λ 5007/H β versus [N ii ] λ 6583/H α , [S ii ] λλ 6717, 6731/H α , and [O i ] λ 6300/H α , and the ionization–metallicity diagram of [O iii ] λ 5007/[O ii ] λ 3727 (O 32 ) versus ([O iii ] λ 5007+[O ii ] λ 3727)/H β ( R 23 ). We also consider a bluer rest-frame ionization–metallicity diagram introduced recently to characterize z > 10 galaxies, [Ne iii ] λ 3869/[O ii ] λ 3727 versus ([Ne iii ] λ 3869+[O ii ] λ 3727)/H δ , as well as longer-wavelength diagnostic diagrams extending into the rest-frame near-IR: [O iii ] λ 5007/H β versus [S iii ] λλ 9069, 9532/[S ii ] λλ 6717, 6731 (S 32 ), and He i λ 1.083 μ m/Pa γ and [S iii ] λ 9532/Pa γ versus [Fe ii ] λ 1.257 μ m/Pa β . With a significant boost in signal-to-noise ratio and large, representative samples of individual galaxy detections, the AURORA emission-line diagrams presented here definitively confirm a physical picture in which chemically young, α -enhanced, massive stars photoionize the interstellar medium (ISM) in distant galaxies with a harder ionizing spectrum at fixed nebular metallicity than in their z ∼ 0 counterparts. We also uncover previously unseen evolution prior to z ∼ 2 in the [O iii ] λ 5007/H β versus [N ii ] λ 6583/H α diagram, which motivates deep NIRSpec observations at even higher redshift. Finally, we present the first statistical sample of rest-frame near-IR emission-line diagnostics in star-forming galaxies at high redshift. In order to truly interpret rest-frame near-IR line ratios including [Fe ii ] λ 1.257 μ m, we must obtain better constraints on dust depletion in the high-redshift ISM.