The Chemodynamics of the Stellar Populations in M31 from APOGEE Integrated-light Spectroscopy

Abstract We present an analysis of nearly 1000 near-infrared, integrated-light spectra from APOGEE in the inner ∼7 kpc of M31. We utilize full-spectrum fitting with A-LIST simple stellar population spectral templates that represent a population of stars with the same age, [M/H], and [ α /M]. With th...

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Published in:	The Astrophysical journal 2023-07, Vol.952 (1), p.23
Main Authors:	Gibson, Benjamin J., Zasowski, Gail, Seth, Anil, Ashok, Aishwarya, Goold, Kameron, Wainer, Tobin, Hasselquist, Sten, Holtzman, Jon, Imig, Julie, Bizyaev, Dmitry, Majewski, Steven R.
Format:	Article
Language:	eng
Subjects:	Abundance Andromeda Galaxy Apogees Astrophysics Galaxies Galaxy abundances Galaxy ages Galaxy bars Galaxy bulges Galaxy disks Galaxy dynamics Galaxy kinematics Galaxy rotation curves Galaxy spectroscopy Galaxy structure Infrared analysis Infrared spectra Kinematics Metallicity Milky Way Near infrared radiation Spectroscopy Spectrum analysis Star & galaxy formation Star formation Stellar populations Velocity distribution
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Summary:	Abstract We present an analysis of nearly 1000 near-infrared, integrated-light spectra from APOGEE in the inner ∼7 kpc of M31. We utilize full-spectrum fitting with A-LIST simple stellar population spectral templates that represent a population of stars with the same age, [M/H], and [ α /M]. With this, we determine the mean kinematics, metallicities, α abundances, and ages of the stellar populations of M31's bar, bulge, and inner disk (∼4–7 kpc). We find a nonaxisymmetric velocity field in M31 resulting from the presence of a bar. The bulge of M31 is less metal-rich (mean [M/H] = − 0.149 − 0.081 + 0.067 dex) than the disk, features minima in metallicity on either side of the bar ([M/H] ∼ −0.2), and is enhanced in α abundance (mean [ α /M] = 0.281 − 0.038 + 0.035 ). The disk of M31 within ∼7 kpc is enhanced in both metallicity ([M/H] = − 0.023 − 0.052 + 0.050 ) and α abundance ([ α /M] = 0.274 − 0.025 + 0.020 ). Both of these structural components are uniformly old at ≃12 Gyr. We find the mean metallicity increases with distance from the center of M31, with the steepest gradient along the disk major axis (0.043 ± 0.021 dex kpc −1 ). This gradient is the result of changing light contributions from the bulge and disk. The chemodynamics of stellar populations encodes information about a galaxy’s chemical enrichment, star formation history, and merger history, allowing us to discuss new constraints on M31's formation. Our results provide a stepping stone between our understanding of the Milky Way and other external galaxies.
ISSN:	0004-637X 1538-4357