Reconstructing chemical enrichment pathways in disc galaxies

A phylogenetic approach

¹ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
² Centro de Astro-ingeniería, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, Santiago, Chile
³ Millenium Nucleus ERIS, Santiago, Chile
⁴ Instituto de Estudios Astrofísicos, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
⁵ Macroevolution and Macroecology, Research School of Biology, Australian National University, Canberra, ACT 0200, Australia
⁶ Mathematical Sciences Institute, Australian National University, Canberra ACT 0200 Australia
⁷ Centre for Astrophysics Research, University of Hertfordshire, Hatfield AL10 9AB, UK
⁸ Departamento de Ingeniería Matemática, Universidad de Chile, Casilla 170 Correo 3, Santiago, Chile
⁹ Inria Chile Research Center, Av. Apoquindo 2827, piso 12, Las Condes, Santiago, Chile
¹⁰ School of Mathematics and Physics, University of Surrey, Guildford, Surrey, GU2 7XH, UK
¹¹ Departamento de Física, Universidad de Santiago de Chile, Av. Victor Jara 3659, Santiago, Chile
¹² Millenium Institute of Astrophysics (MAS), Av. Vicuna Mackenna 4860, 82-0436 Macul, Santiago, Chile
¹³ Center for Interdisciplinary Research in Astrophysics and Space Exploration (CIRAS), Universidad de Santiago de Chile, Santiago, Chile
¹⁴ Leverhulme Centre for Human Evolutionary Studies, Department for Anthropology and Archaeology, University of Cambridge, Fitzwilliam Street., Cambridge CB2 1QH, UK

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 29 September 2025
Accepted: 19 May 2026

Abstract

Context. Phylogenetic methods, traditionally used in biology to trace the evolutionary relationships among species, are emerging as a powerful framework to reconstruct evolutionary processes in galaxies from chemical information.

Aims. We apply galactic phylogenetics to study the chemical evolution of stellar populations in distinct regions of a simulated disc galaxy, assessing its capability to unveil assembly histories.

Methods. We used a high-resolution simulation that followed the chemical enrichment of an isolated disc galaxy by different stellar progenitors. We tracked gas particles as they turned into stars and inherited their parent gas chemical composition. Target particles were selected to store the chemical history of each chemical element considered in the simulation. Two regions were analysed: an inner ring, influenced by early bar-driven inflows, and an outer ring, shaped by spiral arms. We built phylogenetic trees for stellar populations in each region and quantified their structure using the Corrected Colless index, a standard metric of tree balance used in biology.

Results. The inner ring tree reveals a compact clade of old stars enriched by rapid Type II supernova (SNII) feedback, followed by a hierarchical sequence with increasing Type Ia supernova (SNIa) and asymptotic giant branch (AGB) contributions. In contrast, the outer ring exhibits more symmetric, caterpillar-like trees with smoother abundance gradients, consistent with more prolonged star formation and efficient local mixing. Chemical enrichment rates corroborate these trends, showing fast early enrichment in the inner ring and gradual, spatially extended enrichment in the outer disc. The structural indices differ significantly between the two regions and converge robustly even for modest stellar samples (N_SSP = 100).

Conclusions. Galactic phylogenetics provides a novel and complementary tool to decode the fossil record of galaxies. It captures distinct chemical pathways across galactic environments and offers quantitative metrics for comparing assembly histories purely from chemical abundances.