  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--5 microns, and medium spectral
resolution (R~1000), AURORA includes detections of a large suite of nebular
emission lines spanning a broad range in rest wavelength. We investigate the
locations of AURORA galaxies in multiple different emission-line diagrams,
including traditional "BPT" diagrams of [OIII]/Hbeta vs. [NII]/Halpha,
[SII]/Halpha, and [OI]/Halpha, and the "ionization-metallicity" diagram of
[OIII]/[OII] (O32) vs. ([OIII]+[OII])/Hbeta (R23). We also consider a bluer
rest-frame "ionization-metallicity" diagram introduced recently to characterize
z>10 galaxies: [NeIII]/[OII] vs. ([NeIII]+[OII])/Hdelta; as well as
longer-wavelength diagnostic diagrams extending into the rest-frame near-IR:
[OIII]/Hbeta vs. [SIII]/[SII] (S32); and HeI/Pagamma and [SIII]/Pagamma vs.
[FeII]/Pabeta. With a significant boost in signal-to-noise and large,
representative samples of individual galaxy detections, the AURORA
emission-line diagrams presented here definitively confirm a physical picture
in which chemically-young, alpha-enhanced, massive stars photoionize the 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 [OIII]/Hbeta vs. [NII]/Halpha 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 [FeII], we must obtain better constraints on dust
depletion in the high-redshift ISM.
