Year: 2026
Type: article
Abstract: ABSTRACT Radio continuum observations are widely used to study cosmic ray (CR) electron populations and transport processes in star-forming galaxies, but their interpretation relies on several simplifying assumptions. Here, we revisit three common assumptions: that some vertical radio profiles can be explained by CR advection alone, that radio spectra directly trace the galaxy-wide CR electron spectrum, and that bremsstrahlung and Coulomb losses are negligible for radio-emitting electrons. We model radio emission using time-dependent CR electron evolution in a magnetohydrodynamical simulation of an isolated Milky Way-mass galaxy. CR electron spectra are evolved self-consistently along Lagrangian tracer particles with the Crest framework, including injection at supernova remnants, advection with the gas, and spatially and temporally varying radiative losses. We compare these results to commonly adopted steady-state models. We find that advection-only transport in self-consistently driven galactic winds fails to reproduce the extended vertical radio intensity profiles observed in edge-on galaxies, despite reproducing the observed steepening of spectral indices with height. This is because slowly accelerating winds keep electrons in strong cooling environments for too long. Matching observed radio haloes with advection alone requires unrealistically high mid-plane wind velocities, implying that additional transport or re-acceleration processes are required. Although galaxy-integrated CR electron spectra at radio-emitting energies are similar across models, the resulting synchrotron spectra differ systematically because radio emission is biased towards young electrons in dense, strongly magnetized regions. Finally, we show that bremsstrahlung and Coulomb losses significantly shape radio spectra even when their loss rate is subdominant and therefore cannot be neglected.
Language: English
Subfield: Nuclear and High Energy Physics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
Awards: Multimodal single-cell analysis of the Acute Lymphoblastic Leukemia immune landscape, Untersuchungen zur nichtthermischen Emission in Galaxienhaufen: RadioHalos, Relikte, und die fehlende Gammastrahlung, Understanding our Galactic ecosystem: From the disk of the Milky Way to the formation sites of stars and planets, FOR 5195: Relativistische Jets in Aktiven Galaxien, G4523154552, G502385185, Mind the Gap: from Plasma Kinetics to Cosmological Galaxy Formation, G6014366295, G6167709475, Towards a Self-Consistent Multi-Scale Theory of the Feedback-Cycle in Massive Galaxies
OpenAlex ID: W7155501445