The Physical Conditions of Emission-Line Galaxies at Cosmic Dawn from JWST/NIRSpec Spectroscopy in the SMACS 0723 Early Release Observations
Creators: name: Trump, Jonathan R.
name: Haro, Pablo Arrabal
name: Simons, Raymond C.
name: Backhaus, Bren E.
name: Amorín, Ricardo O.
name: Dickinson, Mark
name: Fernández, Vital
name: Papovich, Casey
name: Nicholls, David C.
name: Kewley, Lisa J.
name: Brunker, Samantha W.
name: Salzer, John J.
name: Wilkins, Stephen M.
name: Almaini, Omar
name: Bagley, Micaela B.
name: Berg, Danielle A.
name: Bhatawdekar, Rachana
name: Bisigello, Laura
name: Buat, Véronique
name: Burgarella, Denis
name: Calabrò, Antonello
name: Casey, Caitlin M.
name: Ciesla, Laure
name: Cleri, Nikko J.
name: Cole, Justin W.
name: Cooper, M. C.
name: Cooray, Asantha R.
name: Costantin, Luca
name: Ferguson, Henry C.
name: Finkelstein, Steven L.
name: Fujimoto, Seiji
name: Gardner, Jonathan P.
name: Gawiser, Eric
name: Giavalisco, Mauro
name: Grazian, Andrea
name: Grogin, Norman A.
name: Hathi, Nimish P.
name: Hirschmann, Michaela
name: Holwerda, Benne W.
name: Huertas-Company, Marc
name: Hutchison, Taylor A.
name: Jogee, Shardha
name: Juneau, Stéphanie
name: Jung, Intae
name: Kartaltepe, Jeyhan S.
name: Kirkpatrick, Allison
name: Koekemoer, Anton M.
name: Lotz, Jennifer M.
name: Lucas, Ray A.
name: Magnelli, Benjamin
name: Matharu, Jasleen
name: Pérez-González, Pablo G.
name: Pirzkal, Nor
name: Rafelski, Marc
name: Rose, Caitlin
name: Seillé, Lise-Marie
name: Somerville, Rachel S.
name: Straughn, Amber N.
name: Tacchella, Sandro
name: Vanderhoof, Brittany N.
name: Weiner, Benjamin J.
name: Wuyts, Stijn
name: Yung, L. Y. Aaron
name: Zavala, Jorge A.
Publisher: name: arXiv
Year: 2022
Subjects: subject: Astrophysics of Galaxies (astro-ph.GA)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: We present rest-frame optical emission-line flux ratio measurements for five $z&gt;5$ galaxies observed by the JWST Near-Infared Spectrograph (NIRSpec) in the SMACS 0723 Early Release Observations. We add several quality-control and post-processing steps to the NIRSpec pipeline reduction products in order to ensure reliable relative flux calibration of emission lines that are closely separated in wavelength, despite the uncertain \textit{absolute} spectrophotometry of the current version of the reductions. Compared to $z\sim3$ galaxies in the literature, the $z&gt;5$ galaxies have similar [OIII]$λ$5008/H$β$ ratios, similar [OIII]$λ$4364/H$γ$ ratios, and higher ($\sim$0.5 dex) [NeIII]$λ$3870/[OII]$λ$3728 ratios. We compare the observations to MAPPINGS V photoionization models and find that the measured [NeIII]$λ$3870/[OII]$λ$3728, [OIII]$λ$4364/H$γ$, and [OIII]$λ$5008/H$β$ emission-line ratios are consistent with an interstellar medium that has very high ionization ($\log(Q) \simeq 8-9$, units of cm~s$^{-1}$), low metallicity ($Z/Z_\odot \lesssim 0.2$), and very high pressure ($\log(P/k) \simeq 8-9$, units of cm$^{-3}$). The combination of [OIII]$λ$4364/H$γ$ and [OIII]$λ$(4960+5008)/H$β$ line ratios indicate very high electron temperatures of $4.1&lt;\log(T_e/{\rm K})&lt;4.4$, further implying metallicities of $Z/Z_\odot \lesssim 0.2$ with the application of low-redshift calibrations for ``$T_e$-based'' metallicities. These observations represent a tantalizing new view of the physical conditions of the interstellar medium in galaxies at cosmic dawn.
description: Accepted for publication in AAS Journals. 14 pages, 6 figures, 3 tables