The Physical Conditions of Emission-line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations

We present rest-frame optical emission-line flux ratio measurements for five $z>5$ galaxies observed by the JWST Near-Infared Spectrograph (NIRSpec) in SMACS 0723 Early Release Observations. add several quality-control and post-processing steps to NIRSpec pipeline reduction products order ensure reliable relative calibration of emission lines that are closely separated wavelength, despite uncertain \textit{absolute} spectrophotometry current version reductions. Compared $z\sim3$ literature, have similar [OIII]$\lambda$5008/H$\beta$ ratios, [OIII]$\lambda$4364/H$\gamma$ higher ($\sim$0.5 dex) [NeIII]$\lambda$3870/[OII]$\lambda$3728 ratios. compare observations MAPPINGS V photoionization models find measured [NeIII]$\lambda$3870/[OII]$\lambda$3728, [OIII]$\lambda$4364/H$\gamma$, ratios consistent with an interstellar medium has very high ionization ($\log(Q) \simeq 8-9$, units cm~s$^{-1}$), low metallicity ($Z/Z_\odot \lesssim 0.2$), pressure ($\log(P/k) cm$^{-3}$). The combination [OIII]$\lambda$(4960+5008)/H$\beta$ line indicate electron temperatures $4.1<\log(T_e/{\rm K})<4.4$, further implying metallicities $Z/Z_\odot 0.2$ application low-redshift calibrations ``$T_e$-based'' metallicities. These represent a tantalizing new view physical conditions at cosmic dawn.