2024/10/30 by Benjamin J. Gibson, Gibson, Benjamin J., Gail Zasowski +15
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Stellar, planetary, and galactic studies
paper · pdf · doi:10.48550/arxiv.2410.23340
openalex publication_date 2024/10/30 · openalex created_date 2024/11/14 · openalex updated_date 2026/07/28
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 (R∼4-7 kpc). We use a custom M31 photometric decomposition and A-LIST spectral templates to derive the radial velocity, velocity dispersion, metallicity, and α abundance for both components in each spectrum. In the bulge, one component exhibits little net rotation, high velocity dispersion (∼170 km s-1), near-solar metallicity, and high α abundance ([α/M] = 0.28), while the second component shows structured rotation, lower velocity dispersion (∼121 km s-1), and slightly higher abundances ([M/H] = 0.09, [α/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 α abundance than the second ([M/H] = 0.1 and 0.39, [α/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.