The AURORA Survey: Constraining Chemical Enrichment Pathways at Cosmic Noon with Argon Abundances

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Abstract We present argon abundances from a sample of 46 star-forming galaxies at z = 2−3.5 from the Assembly of Ultradeep Rest-Optical Observations Revealing Astrophysics (AURORA) program. Although argon is an α –element produced by core collapse supernovae (CCSNe), the latest supernova yield models suggest additional argon production and enrichment by Type Ia supernovae (SNe Ia), unlike other α –elements such as oxygen. To study the relationship between argon and oxygen abundances, we construct two median-stacked composite spectra for separate z = 2.0−2.6 and z = 2.8−3.5 redshift bins, presenting more representative measurements than previous samples that require individual detection of faint lines. Abundance ratios were determined using an empirical calibration based on the strength of the [ArIII] λ 7137 emission line relative to the [O III ] λ 5008 emission line. With this calibration, we estimate argon abundances (Ar/O) of 0.4 2 − 0.10 + 0.12 (Ar/O) ⊙ for the 〈 z 〉 = 2.26 bin and 0.4 2 − 0.11 + 0.12 (Ar/O) ⊙ for the 〈 z 〉 = 3.15 bin, suggesting minimal SNe Ia and dominant CCSNe enrichment in this sample. Comparison of our abundance measurements of z ∼ 2−3 AURORA galaxies with chemical evolution modeling of Milky Way stars shows consistency with the Milky Way bulge component, suggesting a rapid star formation timescale. However, even larger samples of actively star-forming galaxies with available argon abundances, as well as comparisons between argon abundance and other critical galaxy properties (e.g., specific star formation rate, sSFR) and models (e.g., one tuned specifically to this redshift range) are needed to draw stronger conclusions on the role of argon in galactic chemical enrichment at cosmic noon.

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