Insight into the physical processes that shape the metallicity profiles in galaxies

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 Astronomía y Física del Espacio, CONICET-UBA, Casilla de Correos 67, Suc. 28, 1428 Buenos Aires, Argentina
⁵ Instituto de Astronomía Teórica y Experimental (IATE, CONICET-Universidad Nacional de Córdoba), Laprida 854, X5000BGR Córdoba, Argentina
⁶ Observatorio Astronómico de la Universidada Nacional de Córdoba, Laprida 854, X5000BGR Córdoba, Argentina
⁷ Departamento de Física Teórica, Universidad Autónoma de Madrid, E-28049 Cantoblanco, Madrid, Spain

^⋆ Corresponding author: brian.tapia@uc.cl

Received: 3 February 2025
Accepted: 23 May 2025

Abstract

Context. The distribution of chemical elements in star-forming regions can store information on the chemical enrichment history of galaxies and particularly of recent events. Negative metallicity gradients are expected in galaxies forming inside-out. Azimuthal-averaged profiles are usually fit to the projected chemical distributions to quantify them. However, observations show that the metallicity profiles can be broken.

Aims. We aim to study the diversity of metallicity profiles that can arise in the current cosmological context and compare them with available observations. Additionally, we seek to identify the physical processes responsible for breaks in metallicity profiles by using two galaxies as case studies.

Methods. We analyzed central galaxies from the cosmological simulations of CIELO project, with stellar masses within the range of 10^8.5 to 10^10.5 M_⊙ at z = 0. A new algorithm, DB-A, was developed to fit multiple power laws to the metallicity profiles, enabling a flexible assessment of metallicity gradients in various galactic regions. The simulations include detailed modeling of gas components, metal-dependent cooling, star formation, and supernova feedback.

Results. At z = 0, we find a diversity of shapes, with inner and outer drops and rises, and there are a few galaxies with double breaks. Inner, outer, and middle gradients are in agreement with observations. We also find that using a single linear regression to fit gradients usually traces the middle gradient well. A detailed temporal analysis of the main galaxies of a Local Group analog revealed the occurrence of inner and outer breaks at all cosmic times, with the latter being the most common feature during the evolution of our case studies. Significant variability in the metallicity gradients was found at high redshift, transitioning to more gradual evolution at lower redshifts. Most of the inner breaks have enhanced oxygen abundances in the center, which are linked to gas accretion followed by efficient star formation. Inner breaks with diluted oxygen abundances are less common and are found in galaxies with disrupted gas distributions which are affected by feedback-driven ejection of enriched gas. Outer breaks with high abundances are linked to processes such as the re-accretion of enriched material, extended star formation, and enhanced gas mixing from the circumgalactic medium. Outer breaks with diluted metallicities in the outskirts are found mainly at high redshift and are associated with the accretion of metal-poor gas from cold flows. We also highlight and illustrate the complex interplay of these processes which act often together.