Towards understanding the Milky Way’s typicality: assessing the chemodynamics of M31’s bulge and bar, thick and thin discs

ABSTRACT We describe a novel framework to model galaxy spectra with two cospatial stellar populations, such as may represent a bulge and bar or thick and thin disc, and apply it to APOGEE spectra in the inner $\sim$2 kpc of M31, as well as to stacked spectra representative of the northern and southern parts of M31’s disc ($R\sim 4\!-\!7$ kpc). We use a new unWISE-based photometric decomposition of M31 that includes a Sérsic bulge, bar, and exponential disc. This informs our full-spectrum fitting with A-LIST spectral templates to derive the radial velocity, velocity dispersion, metallicity, and $\alpha$ abundance for both components in each spectrum. In the bulge, one component exhibits little net rotation, high velocity dispersion ($\sim$170 km s$^{-1}$), an average [M/H] = 0.07, and average [$\alpha$/M] = 0.29, while the second component shows structured rotation, lower velocity dispersion ($\sim$121 km s$^{-1}$), and similar average abundances. We also constrain the abundance gradients for each of these components. 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 $\alpha$ abundance than the second ([M/H] = 0.1 and 0.39, [$\alpha$/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. Such multipopulation analysis is crucial to constrain galaxy evolution models that strive to recreate the complex stellar populations found in the Milky Way.

Authors

Institutions

Publication Details

Journal
Monthly Notices of the Royal Astronomical Society
Published
2025-08-14
DOI
https://doi.org/10.1093/mnras/staf1115
Citations
1
Primary Topic
Stellar, planetary, and galactic studies
Type
article
Field-Weighted Citation Impact
1.15

Funders

Controls
|||
ALL TIME
JAN
FEB
MAR
APR
MAY
JUN
JUL
AUG
SEP
OCT
article

Towards understanding the Milky Way’s typicality: assessing the chemodynamics of M31’s bulge and bar, thick and thin discs

Jon A. Holtzman, Sanjib Sharma, Z. Wang, Dmitry Bizyaev et al.
1 citations
Monthly Notices of the Royal Astronomical Society
Stellar, planetary, and galactic studies
1.15
article

Towards understanding the Milky Way’s typicality: assessing the chemodynamics of M31’s bulge and bar, thick and thin discs

Jon A. Holtzman, Sanjib Sharma, Z. Wang, Dmitry Bizyaev, Dimitri Alexei Gadotti, Gail Zasowski, Benjamin J. Gibson, Anil C. Seth, Steven R. Majewski
article en
1 citations

Abstract

ABSTRACT We describe a novel framework to model galaxy spectra with two cospatial stellar populations, such as may represent a bulge and bar or thick and thin disc, and apply it to APOGEE spectra in the inner $\sim$2 kpc of M31, as well as to stacked spectra representative of the northern and southern parts of M31’s disc ($R\sim 4\!-\!7$ kpc). We use a new unWISE-based photometric decomposition of M31 that includes a Sérsic bulge, bar, and exponential disc. This informs our full-spectrum fitting with A-LIST spectral templates to derive the radial velocity, velocity dispersion, metallicity, and $\alpha$ abundance for both components in each spectrum. In the bulge, one component exhibits little net rotation, high velocity dispersion ($\sim$170 km s$^{-1}$), an average [M/H] = 0.07, and average [$\alpha$/M] = 0.29, while the second component shows structured rotation, lower velocity dispersion ($\sim$121 km s$^{-1}$), and similar average abundances. We also constrain the abundance gradients for each of these components. 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 $\alpha$ abundance than the second ([M/H] = 0.1 and 0.39, [$\alpha$/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. Such multipopulation analysis is crucial to constrain galaxy evolution models that strive to recreate the complex stellar populations found in the Milky Way.

Monthly Notices of the Royal Astronomical SocietyVol. 542(2)
New Mexico State University (US), Space Telescope Science Institute (US), Durham University (GB), University of Utah (US), National Solar Observatory (US), Université Bourgogne Franche-Comté (FR), University of Virginia (US)
National Science Foundation, Smithsonian Institution, U.S. Department of Energy, National Aeronautics and Space Administration, Alfred P. Sloan Foundation, Yale University, Carnegie Institution of Washington, Vanderbilt University, Ohio State University, California Institute of Technology, University of Utah, University of Washington, Johns Hopkins University, Carnegie Mellon University, University of Notre Dame, University of Portsmouth, New Mexico State University, Space Telescope Science Institute, York University, University of Oxford, Ministério da Ciência, Tecnologia e Inovação, University of Tokyo, Universidad Nacional Autónoma de México, Max-Planck-Institut für Astrophysik, Max-Planck-Institut für Astronomie, Instituto de Astrofísica de Canarias, Office of Science, Jet Propulsion Laboratory, University of California, Los Angeles, University of Colorado Boulder, Smithsonian Astrophysical Observatory, Science and Technology Facilities Council, Leibniz-Gemeinschaft, Lawrence Berkeley National Laboratory
Openalex Percentile: Top 17%
Stellar, planetary, and galactic studies
1.15
DOIOpen Access PDFOpenAlex
AI Navigator

Ask Laika to Summarize, Analyze, and Connect papers live on the map.

Summarize Papers & Methodologies

Extract key findings, datasets, and comparative methods across publications.

Benchmark Rankings & Visual Analytics

Rank top research institutions, authors, funders, topics, and journals by Field-Weighted Citation Impact (FWCI) and paper volume with instant charts.

Connect Distant Disciplines

Bridge topological clusters on the map to find hidden collaborative intersections.