paper

Towards Understanding the Milky Way's Typicality: Assessing the Chemodynamics of M31's Bulge & Bar, Thick & Thin Discs

arXiv:2410.23340 · doi:10.1093/mnras/staf1115

Abstract

We describe a novel framework to model galaxy spectra with two cospatial stellar populations, such as may represent a bulge & bar or thick & thin disc, and apply it to APOGEE spectra in the inner 2 kpc of M31, as well as to stacked spectra representative of the northern and southern parts of M31's disc ( kpc). We use a custom M31 photometric decomposition and A-LIST spectral templates to derive the radial velocity, velocity dispersion, metallicity, and abundance for both components in each spectrum. In the bulge, one component exhibits little net rotation, high velocity dispersion (170 km s), near-solar metallicity, and high abundance ([/M] = 0.28), while the second component shows structured rotation, lower velocity dispersion (121 km s), and slightly higher abundances ([M/H] = 0.09, [/M] = 0.3). We tentatively associate the first component with the classical bulge and the second with the bar. In the north disc we identify two distinct components: the first with hotter kinematics, lower metallicity, and higher abundance than the second ([M/H] = 0.1 and 0.39, [/M] = 0.29 and 0.07). These discs appear comparable to the Milky Way's ''thick'' and ''thin'' discs, providing the first evidence that M31's inner disc has a similar chemodynamical structure. We do not identify two distinct components in the south, potentially due to effects from recent interactions. Such multi-population analysis is crucial to constrain galaxy evolution models that strive to recreate the complex stellar populations found in the Milky Way.

16 pages, 9 figures

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