The chemical abundances of spiral galaxies, as probed by H II regions across their disks, are key to understanding the evolution of galaxies over a wide range of environments. We present LBT/MODS spectra of 52 H II regions in NGC3184 as part of the CHemical Abundances Of Spirals (CHAOS) project. We explore the direct-method gas-phase abundance trends for the first four CHAOS galaxies, using temperature measurements from one or more auroral line detections in 190 individual H II regions. We find the dispersion in T e − T e relationships is dependent on ionization, as characterized by F λ5007 /F λ3727 , and so recommend ionization-based temperature priorities for abundance calculations. We confirm our previous results that [N II] and [S III] provide the most robust measures of electron temperature in low-ionization zones, while [O III] provides reliable electron temperatures in highionization nebula. We measure relative and absolute abundances for O, N, S, Ar, and Ne. The four CHAOS galaxies marginally conform with a universal O/H gradient, as found by empirical IFU studies when plotted relative to effective radius. However, after adjusting for vertical offsets, we find a tight universal N/O gradient of α N/O = −0.33 dex/R e with σ tot. = 0.08 for R g /R e < 2.0, where N is dominated by secondary production. Despite this tight universal N/O gradient, the scatter in the N/O-O/H relationship is significant. Interestingly, the scatter is similar when N/O is plotted relative to O/H or S/H. The observable ionic states of S probe lower ionization and excitation energies than O, which might be more appropriate for characterizing abundances in metal-rich H II regions. Spectral ReductionsFor a detailed description of the data reduction procedures we refer the reader to (B15). Here, we only note the primary points of our data processing. Spectra were reduced and analyzed using the beta-version of the MODS reduction pipeline 1 which runs within the XIDL 2 reduction package. Given that the bright disks of CHAOS galaxies can complicate local sky subtraction, 1

We report the direct abundances for the galaxy NGC 2403 as observed by the CHemical Abundances Of Spirals (CHAOS) project. Using the Multi-Object Double Spectrograph on the Large Binocular Telescope, we observe two fields with H ii regions that cover an R g /R e range of 0.18–2.31. Thirty-two H ii regions contain at least one auroral line detection, and we detect a total of 122 temperature-sensitive auroral lines. Here, for the first time, we use the intrinsic scatter in the T e –T e diagrams, added in quadrature to the uncertainty on the measured temperature, to determine the uncertainty on an electron temperature inferred for one ionization zone from a measurement in a different ionization zone. We then use all available temperature data within a H ii region to obtain a weighted-average temperature within each ionization zone. We rederive the oxygen abundances of all CHAOS galaxies using this new temperature prioritization method, and we find that the gradients are consistent with the results of a recent study of Berg et al. For NGC 2403, we measure a direct oxygen abundance gradient of −0.09(±0.03) dex/R e , with an intrinsic dispersion of 0.037(±0.017) dex and a N/O abundance gradient of −0.17(±0.03) dex/R e with an intrinsic dispersion of 0.060(±0.018) dex. For direct comparison, we use the line intensities from an earlier study of NGC 2403 by Berg et al. and find their recomputed values for the O/H and N/O gradients are consistent with ours.

We analyze the rest-frame near-UV and optical nebular spectra of three z > 7 galaxies from the Early Release Observations taken with the Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope (JWST). These three high-z galaxies show the detection of several strong emission nebular lines, including the temperature-sensitive [O iii] λ4363 line, allowing us to directly determine the nebular conditions and abundances for O/H, C/O, and Ne/O. We derive O/H abundances and ionization parameters that are generally consistent with other recent analyses. We analyze the mass–metallicity relationship (i.e., slope) and its redshift evolution by comparing between the three z > 7 galaxies and local star-forming galaxies. We also detect the C iii] λλ1907, 1909 emission in a z > 8 galaxy from which we determine the most distant C/O abundance to date. This valuable detection of log(C/O) = −0.83 ± 0.38 provides the first test of C/O redshift evolution out to high redshift. For neon, we use the high-ionization [Ne iii] λ3869 line to measure the first Ne/O abundances at z > 7, finding no evolution in this α-element ratio. We explore the tentative detection of [Fe ii] and [Fe iii] lines in a z > 8 galaxy, which would indicate a rapid buildup of metals. Importantly, we demonstrate that properly flux-calibrated and higher-S/N spectra are crucial to robustly determine the abundance pattern in z > 7 galaxies with NIRSpec/JWST.

Ultraviolet light from early galaxies is thought to have ionized gas in the intergalactic medium. However, there are few observational constraints on this epoch, due to the faintness of those galaxies and the redshift of their optical light into the infrared. We report the observation, in James Webb Space Telescope (JWST) imaging, of a distant galaxy that is magnified by gravitational lensing. JWST spectroscopy of the galaxy, at rest-frame optical wavelengths, detects strong nebular emission lines due to oxygen and hydrogen. The measured redshift is z = 9.51 ± 0.01, corresponding to 510 million years after the Big Bang. The galaxy has a radius of 16.2 − 7.2 + 4.6 parsecs, substantially more compact than galaxies with equivalent luminosity at z ~ 6 to 8, leading to a high star formation rate surface density.

Given their extremely faint apparent brightness, the nature of the first galaxies and how they reionized the Universe's gas are not yet understood. Here we report the discovery, in James Webb Space Telescope (JWST) imaging, of a highly magnified, low-mass (log(M * /M ) = 7.70 +0.11 −0.09 ) galaxy visible when the Universe was only 510 Myr old, and follow-up prism spectroscopy of the galaxy extending from Lyman α to [O III] λ5007 in its rest frame. Our JWST spectrum provides [O III] λ5007 and Hβ detections with a respective signalto-noise ratio (S/N) of 33 and 7, as well as four additional lines with S/N > 2. These emission lines yield a redshift of z = 9.51 and star-formation rate of 0.26 +0.07 −0.05 M yr −1 . The galaxy's large inferred value of [O III]/[O II] = 16 ± 6 suggests that this galaxy has an escape fraction of ionizing radiation larger than 10%, indicating that a population of similar objects could contribute substantially to the reionization budget. Using multiple techniques, we infer a gas oxygen abundance of 12 + log(O/H) = 7.47 ± 0.10 dex, consistent within 2σ of the mass-metallicity relation observed for dwarf galaxies in the local Universe.With the advent of JWST, we can now see deeper into the early Universe than ever before.JWST's 6.5 m mirror and highly sensitive near-infrared instruments extending to 5 µm theoretically allow for the detection of rest-frame optical emission from galaxies at redshifts as high as z ≈ 20 (1), far surpassing the capabilities of its predecessor the Hubble Space Telescope (HST).The ability to detect and analyze galaxies at unprecedented redshifts opens the door for a new understanding of the physical processes which govern galaxy formation and evolution.