First JWST Results Find No Alpha-Bimodality in M31

Nidever, David; Gilbert, Karoline; Tollerud, Erik; Siders, Charles; Escala, Ivanna; Allende Prieto, Carlos; Smith, Verne; Cunha, Katia; Debattista, Victor; Ting, Yuan-Sen; Kirby, Evan; Guhathakurta, Puragra
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American Astronomical Society Meeting Abstracts

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The recent era of large, ground-based abundance surveys has unraveled the chemical structures of our Milky Way galaxy. The most striking abundance feature is the alpha-abundance bimodality. The low-alpha stars are younger (1-8 Gyr) while the high-alpha stars are older (8-12 Gyr) and have a thicker distribution. While there are a number of models that can reproduce the Milky Way alpha-bimodality, none are strongly favored by the data. However, they do make different predictions about the prevalence of the alpha-bimodality in Milky Way-mass galaxies. Our Cycle 1 JWST NIRspec program has obtained high-S/N, medium-resolution spectra of over 100 stars in one M31 disk field. We have measured stellar parameters, radial velocities, and alpha-abundances using a set of synthetic spectra. No alpha-bimodality exists in the M31 JWST abundances and the data can be explainedy by a single, high star formation efficiency evolutionary track similar to what is seen in the MW bulge. While this result is somewhat surprising, the larger accretion and merger rate of M31 is likely responsible for the different chemical pattern.