The universality of the relation between magnetic fields and star formation in galaxies

¹ DIFA, Università di Bologna, Via Gobetti 93/2, I-40129 Bologna, Italy
² INAF, Istituto di Radioastronomia, Via Gobetti 101, I-40129 Bologna, Italy
³ Kavli Institute for Particle Astrophysics & Cosmology (KIPAC), Stanford University, Stanford, CA 94305, USA
⁴ Department of Physics & Astronomy, University of South Carolina, Columbia, SC 29208, USA
⁵ ESO, Karl Schwarzchild Srt. 2, 85478 Garching bei München, Germany

^★ Corresponding author.

Received: 29 October 2025
Accepted: 2 February 2026

Abstract

Context. The interstellar medium (ISM) is permeated by magnetic fields affecting gas dynamics and star formation. These magnetic fields have been observed to be related to the supernova-driven turbulence. However, whether this scaling is universal across galaxy properties, star formation levels, ISM phases, and energy budgets remains unclear.

Aims. We quantify the dependence of magnetic fields on the star formation activity, spanning seven orders of magnitude, and encompassing regular and starburst galaxies. In addition, we study the energetic balance of the multi-phase ISM for thermal and non-thermal (turbulent, cosmic-ray) components.

Methods. We analysed 19 spiral disc galaxies from the cosmological RTnsCRiMHD AZAHAR-A suite. For each system we built line-of-sight–integrated maps, selected the inner star-forming disc, and measured the median magnetic field strength, star formation rate (SFR), surface density (Σ_SFR), specific SFR (sSFR), as well as the thermal, turbulent, magnetic, and cosmic-ray specific energies.

Results. We find an approximately universal magnetic field strength B–SFR scaling with α ≃ 0.2 − 0.3 across galaxy mass, inclination, and neutral phases (cold and warm). The B–Σ_SFR slope α_Σ ∼ 1/3 is in agreement with a SN-driven, turbulence-regulated magnetic field. The B–sSFR relation provides the best separation across galaxy types and multiphase ISM. We find all specific non-thermal energies to increase with SFR, with the magnetic component having the highest slope. Energetically, neutral gas in the simulations is typically turbulence-dominated with a secondary contribution from cosmic rays, and in approximate equipartition with magnetic energies for systems with significant star formation (sSFR ≳ 0.1 Gyr⁻¹, SFR ≳ 1 M_⊙ yr⁻¹). The trends of our simulations are consistent with observations, which show similar slopes (α ≈ 0.25 − 0.35) across a wide range of galaxy types and environments.

Conclusions. Our results show that SN-driven turbulence is the main amplification mechanism yielding the near-universal B-SFR. This results in magnetic fields playing a dynamical role in the neutral ISM in galaxies with intense star formation.