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Chemical enrichment of the thin and thicker discs of Andromeda: Oxygen to argon abundance ratios for planetary nebulae

Published online by Cambridge University Press:  30 October 2025

M. Arnaboldi Open the ORCID record for M. Arnaboldi [Opens in a new window] ,
S. Bhattacharya Open the ORCID record for S. Bhattacharya [Opens in a new window] ,
O. Gerhard Open the ORCID record for O. Gerhard [Opens in a new window]  and
C. Kobayashi Open the ORCID record for C. Kobayashi [Opens in a new window]
M. Arnaboldi*
Affiliation:
European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
S. Bhattacharya
Affiliation:
Inter University Centre for Astronomy and Astrophysics, Ganeshkhind, Post Bag 4, Pune 411007, India
O. Gerhard
Affiliation:
Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
C. Kobayashi
Affiliation:
Centre for Astrophysics Research, Department of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield AL10 9AB, UK
*
email: marnabol@eso.org
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Abstract

We use oxygen and argon abundances for planetary nebulae (PNe) with low internal extinction (progenitor ages of > 4.5 Gyr) and high extinction (progenitor ages < 2.5 Gyr), as well as those of the HII regions, to constrain the chemical enrichment and star formation efficiency in the thin and thicker discs of M31. As the argon element is produced in larger fractions by Type Ia supernovae compared to oxygen, we found that the mean log(O/Ar) values of PNe as a function of their argon abundances [12 + log(Ar/H)] trace the interstellar medium (ISM) conditions at the time of birth of the M31 disc PN progenitors. Thus, the chemical enrichment and star formation effciency information encoded in the [α/Fe] versus [Fe/H] distribution of stars is also imprinted in the oxygen-to-argon abundance ratio log(O/Ar) versus argon abundance for the nebular emissions of the different stellar evolution phases. The chemical evolution model that reproduces the mean log(O/Ar) values as a function of argon abundance for the high- and low-extinction PNe requires a second infall of metal-poorer gas during a gas-rich (wet) satellite merger for the M31 disc region within 14 kpc. A strong starburst is ongoing in the intermediate radial range (14 < RGC< 18 kpc). In the outer M31 disc (RGC > 18 kpc), the log(O/Ar) versus argon abundance distribution of the younger high-extinction PNe indicates that they too were formed in a burst, though mostly from the metal-poorer gas. In M31, the thin disc is younger and less radially extended, formed stars at a higher star formation effciency, and had a faster chemical enrichment timescale than the more extended thicker disc. Both the thin and thicker discs in M31 reach similar high argon abundances (12 + log(Ar/H))∼ 6.7. The chemical and structural properties of the thin and thicker discs in M31 are thus remarkably different from those determined for the Milky Way thin and thick discs.

Keywords

stars: AGB and post-AGBplanetary nebulae: generalstars: abundancesgalaxies: individual: M31galaxies: structure

Information

Type
Poster Paper
Information
Proceedings of the International Astronomical Union , Volume 19 , Symposium S379: Dynamical Masses of Local Group Galaxies , December 2023 , pp. 10 - 14
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Copyright
© The Author(s), 2025. Published by Cambridge University Press on behalf of International Astronomical Union

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