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The heavy element content ("metallicity") of the Universe is a record of the total star formation history. Gas-phase metallicity in galaxies, as well as its evolution with time, is of particular interest as a tracer of accretion and outflow processes. However, metallicities from the widely-used electron temperature (Te) method are typically ~2 times lower than the values based on the recombination line method. This "abundance discrepancy factor" (ADF) is well known and is commonly ascribed to bias due to temperature fluctuations. We present a measurement of oxygen abundance in the nearby (3.4 Mpc) system, Mrk 71, using a combination of optical and far-IR emission lines to measure and correct for temperature fluctuation effects. Our far-IR result is inconsistent (~2.5σ significance) with the metallicity from recombination lines and instead indicates little to no bias in the standard Te method, ruling out the long-standing hypothesis that the ADF is explained by temperature fluctuations for this object. Our results provide a framework to accurately measure metallicity across cosmic history, including with recent data reaching within the first billion years with JWST and the Atacama Large Millimeter Array (ALMA).

Galaxies have formed from the repeated mergers of small star-forming clumps over cosmic time, with some small galaxies left over even today, such as the Magellanic clouds. JWST has now discovered two such small galaxies within the first 430 billion years, that are seen close to the very start of this process. MACS0647--JD is a triply-lensed $z \sim 11$ galaxy originally discovered with the \emph{Hubble Space Telescope}. Here we report new JWST imaging, which clearly resolves MACS0647--JD as having two components that are either merging galaxies or stellar complexes within a single galaxy. The brighter larger component ``A'' is intrinsically very blue ($\beta \sim -2.6$), likely due to very recent star formation and no dust, and is spatially extended with an effective radius $\sim70\,{\rm pc}$. The smaller component ``B'' appears redder ($\beta \sim -2$), likely because it is older (100--200\,Myr) with mild dust extinction ($A_V \sim 0.1$\,mag), and a smaller radius $\sim20\,{\rm pc}$. We identify galaxies with similar colors in a high-redshift simulation, finding their star formation histories to be out of phase. JWST NIRSpec observations planned for January 2023 will deliver a spectroscopic redshift and a more detailed study of the physical properties of MACS0647--JD.