Metal-loaded outflows in sub-Milky Way galaxies in the CIELO simulations

¹ Instituto de Astrofísica, Pontificia Universidad Católica de Chile Av. Vicuña Mackenna 4860 7820436 Santiago, Chile
² Centro de Astro-Ingeniería, Pontificia Universidad Católica de Chile Av. Vicuña Mackenna 4860 7820436 Santiago, Chile
³ Instituto de Astronomía y Física del Espacio, CONICET-UBA, Casilla de Correos 67 Suc. 28 1428 Buenos Aires, Argentina
⁴ Departamento de Física Teórica, Universidad Autónoma de Madrid E-28049 Cantoblanco Madrid, Spain

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

Received: 1 August 2025
Accepted: 15 December 2025

Abstract

Context. Supernova (SN) feedback-driven galactic outflows are a key physical process that contributes to the baryon cycle by regulating star formation activity, reducing the amount of metals in low-mass galaxies and enriching the circumgalactic (CGM) and intergalactic media (IGM).

Aims. We aim to understand the chemical loop of sub-Milky Way (MW) galaxies and their nearby regions.

Methods. We studied 15 simulated central sub-MW galaxies (M_∗ ≤ 10¹⁰ M_⊙) and intermediate-mass galaxies (M_* ∼ 10¹⁰ M_⊙) from the CIELO-P7 high-resolution simulations. We followed the evolution of the progenitor galaxies, their properties, and the characteristics of the outflows within the redshift range z = [0, 7]. We used two dynamically motivated outflow definitions, unbound outflows, and expelled mass rates to quantify the impact of SN feedback.

Results. At z ∼ 0, sub-MW galaxies have a larger fraction of their current oxygen mass in the gas phase but have expelled a greater portion beyond the virial radius, compared to their higher-mass counterparts. Galaxies with M_∗ < ∼ 10⁹ M_⊙ have 10–40 percent of their total oxygen mass within R₂₀₀ in the CGM and an equivalent to 10–60 percent expelled into the IGM. In contrast, more massive galaxies have most of their oxygen mass locked by the stellar populations. The CGM of low-mass galaxies predominantly contains oxygen low-temperature gas, which acts as a metal reservoir. We find that the outflows are more oxygen-rich for sub-MW galaxies, Z_out/Z_ISM ∼ 1.5, than for higher-mass galaxies, Z_out/Z_ISM ≤ 0.5, particularly for z < 2. Mass-loading factors of η_out ∼ 0 − 6 are detected, in agreement with observations. While a weak dependence of η on mass and circular velocity is found at z ∼ 0, a stronger anti-correlation appears for higher redshift.

Conclusions. Our results suggest that sub-MW galaxies may store a significant fraction of metals in their CGM and that the anti-correlation between η and stellar mass (or circular velocity) is stronger at z ∼ 2, which is likely due to a combination of more intense star formation, a higher merger rate, and shallower potential wells.