Reconstructing the Milky Way chemical map with the galactic chemical evolution tool OMEGA+ from SDSS-MWM

¹ ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, 9700 Szombathely, Szent Imre H. st. 112, Hungary
² ELTE Eötvös Loránd University, Institute of Physics and Astronomy, Budapest 1117, Pázmány Péter sétány 1/A, Hungary
³ MTA-ELTE Lendület “Momentum” Milky Way Research Group, Hungary
⁴ Konkoly Observatory, HUN-REN CSFK/RCAES, Konkoly Thege Miklós út 15–17, 1121 Budapest, Hungary
⁵ The Oskar Klein Centre, Department of Astronomy, Stockholm University, AlbaNova, 10691 Stockholm, Sweden
⁶ CSFK HUN-REN, MTA Centre of Excellence, Budapest, Konkoly Thege Miklós út 15–17., 1121 Budapest, Hungary
⁷ E. A. Milne Centre for Astrophysics, University of Hull, Cottingham Road, Kingston upon Hull, HU6 7RX, UK
⁸ NuGrid Collaboration, http://nugridstars.org
⁹ Center for Astrophysics and Space Astronomy, Department of Astrophysical and Planetary Sciences, University of Colorado, 389 UCB, Boulder, CO 80309-0389, USA
¹⁰ Departamento de Física, Universidade Federal de Sergipe, Av. Marcelo Deda Chagas, S/N, 49107-230 São Cristóvão, SE, Brazil
¹¹ School of Physics and Astronomy, Monash University, VIC 3800, Australia

^★ Corresponding author.

Received: 29 January 2025
Accepted: 29 May 2025

Abstract

Context. Although current observations indicate that there are two distinct sequences of disk stars in the [α/M] versus [M/H] parameter space, further complexity is evident in the chemical makeup of the Milky Way and consequently suggests a complicated evolutionary history.

Aims. We developed two-infall galactic chemical evolution (GCE) models consistent with the Galactic chemical map.

Methods. We obtained new GCE models simulating the chemical evolution of the Milky Way, as constrained by a golden sample of 394 000 stellar abundances of the Milky Way Mapper survey from data release 19 of SDSS-V. The separation between the chemical thin and thick disks was defined using [Mg/M]. We used the chemical evolution environment OMEGA+ combined with Levenberg-Marquardt (LM) and bootstrapping algorithms for the optimization and error estimation. We simulated the entire Galactic disk and considered six galactocentric regions, allowing for a more detailed analysis of the formation of the inner, middle, and outer Galaxy. We investigated the evolution of α, odd-Z, and iron-peak elements, covering 15 species altogether.

Results. The chemical thin and thick disks are separated by Mg observations, which the other α-elements show similar trends with, while odd-Z species demonstrate different patterns as functions of metallicity. In the inner Galactic disk regions, the locus of the low-Mg sequence is gradually shifted toward higher metallicity, while the high-Mg phase is less populated. The best-fit GCE models show a well-defined peak in the rate of the infalling matter as a function of the Galactic age, confirming a merger event about 10 Gyr ago. We show that the timescale of gas accretion, the exact time of the second infall and the ratio between the surface mass densities associated with the second infall event and the formation event vary with the distance from the Galactic center. According to the models, the disk was assembled within a timescale of (0.32±0.02) Gyr during a primary formation phase, followed by an increasing accretion rate over a (0.55±0.06) Gyr-timescale and a relaxation phase that lasted (2.86±0.70) Gyr, with a second peak seen for the infall rate at (4.13±0.19) Gyr.

Conclusions. Our best Galaxy evolution models are consistent with an inside-out formation scenario of the Milky Way disk and in agreement with the findings of recent chemodynamical simulations.