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

Abstract

The interstellar medium (ISM) is permeated by magnetic fields that affect gas dynamics and star formation. These fields correlate with supernova (SN)-driven turbulence, but whether the scaling is universal across galaxy properties, ISM phases, and energy budgets remains unclear. We quantify the dependence of magnetic fields on star formation activity including both regular and starburst galaxies. We analyse 19 spiral disks from the cosmological RTnsCRiMHD Azahar suite, deriving line-of-sight integrated maps to measure median magnetic-field strength ($B$), specific energies (thermal, turbulent, magnetic, and cosmic-ray), and star formation rate (SFR), star formation surface density ($\Sigma_{\mathrm{SFR}}$) and specific SFR (sSFR). We find an almost universal magnetic-field-SFR scaling with slope $\alpha \approx 0.2$-$0.3$ across galaxy mass and ISM phases. The $B$-$\Sigma_{\mathrm{SFR}}$ slope ($\alpha \approx 1/3$) supports an SN-driven, turbulence-regulated origin. Neutral gas is generally turbulence-dominated and in near equipartition with magnetic energy for systems with sSFR $\gtrsim 0.1$ Gyr$^{-1}$ and SFR $\gtrsim 1$ $M_\odot$ yr$^{-1}$. The simulated trends match observations with similar slopes ($\alpha \approx 0.25$-$0.35$), indicating that SN-driven turbulence is the main amplification mechanism behind the near-universal $B$-SFR relation.