CHANG-ES. XLII. Cosmic-Ray Electron Transport and the Spatially Resolved Radio–SFR Relation in Edge-on Galaxies
8 affiliations
- 1University of Science and Technology of China
- 2Universität Hamburg
- 3Chinese Academy of Sciences
- 4Max-Planck-Institut für Radioastronomie
- 5Qinghai University
- 6Xiangtan University
- 7University of Manitoba
- 8Yunnan University
Abstract
Radio continuum emission traces star formation in galaxies, but cosmic-ray electron (CRE) propagation between the disk and halo complicates this connection. We present a wide-band, spatially resolved analysis of 19 nearby edge-on galaxies, combining LOFAR observations at 144 MHz with CHANG-ES VLA imaging at 1.575, 3.0, and 6.0 GHz, and hybrid H α +22 μ m star formation rate (SFR) maps. All maps are convolved to a common 2.1 kpc resolution for pixel-by-pixel analysis of the nonthermal spectral index α nth and the SFR surface density Σ SFR . All 19 galaxies exhibit statistically significant nonthermal spectral flattening with increasing Σ SFR , with a sample median slope of 0.1 9 − 0.03 + 0.09 that traces the contrast between CRE injection in the star-forming disk and cooling in the halo. The galaxy-to-galaxy scatter in this slope shows no dependence on global galaxy properties and instead appears to be modulated by the local dynamical environment, with the largest α nth –Σ SFR slopes appearing in tidally perturbed systems. The resolved radio–SFR slope steepens from 0.57 at 144 MHz to 0.95 at 6 GHz, approaching linearity at high frequencies. This trend is consistent with energy-dependent CRE cooling and transport, with the deviation from linearity most pronounced at low frequencies, where the edge-on line of sight blends midplane and halo CRE populations. These results are robust against thermal contamination, beam smearing, and spectral curvature. Together, our analysis establishes α nth as an observational probe of projected disk-to-halo CRE transport in edge-on galaxies and quantifies how this transport reshapes the frequency dependence of resolved radio–SFR calibrations.
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BibTeX
@article{xu2026changes,
title = {{CHANG-ES. XLII. Cosmic-Ray Electron Transport and the Spatially Resolved Radio–SFR Relation in Edge-on Galaxies}},
author = {Jianghui Xu and Volker Heesen and Jiang-Tao Li and Guilin Liu and Rainer Beck and Li-Yuan Lu and Yang Yang and Jayanne English and Shengtao Wang},
journal = {The Astrophysical Journal},
year = {2026},
month = nov,
doi = {10.3847/1538-4357/aead99},
url = {https://iopscience.iop.org/article/10.3847/1538-4357/aead99},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - CHANG-ES. XLII. Cosmic-Ray Electron Transport and the Spatially Resolved Radio–SFR Relation in Edge-on Galaxies
AU - Jianghui Xu
AU - Volker Heesen
AU - Jiang-Tao Li
AU - Guilin Liu
AU - Rainer Beck
AU - Li-Yuan Lu
AU - Yang Yang
AU - Jayanne English
AU - Shengtao Wang
PY - 2026
DA - 2026/11/03
JO - The Astrophysical Journal
DO - 10.3847/1538-4357/aead99
UR - https://iopscience.iop.org/article/10.3847/1538-4357/aead99
AB - Radio continuum emission traces star formation in galaxies, but cosmic-ray electron (CRE) propagation between the disk and halo complicates this connection. We present a wide-band, spatially resolved analysis of 19 nearby edge-on galaxies, combining LOFAR observations at 144 MHz with CHANG-ES VLA imaging at 1.575, 3.0, and 6.0 GHz, and hybrid H α +22 μ m star formation rate (SFR) maps. All maps are convolved to a common 2.1 kpc resolution for pixel-by-pixel analysis of the nonthermal spectral index α nth and the SFR surface density Σ SFR . All 19 galaxies exhibit statistically significant nonthermal spectral flattening with increasing Σ SFR , with a sample median slope of 0.1 9 − 0.03 + 0.09 that traces the contrast between CRE injection in the star-forming disk and cooling in the halo. The galaxy-to-galaxy scatter in this slope shows no dependence on global galaxy properties and instead appears to be modulated by the local dynamical environment, with the largest α nth –Σ SFR slopes appearing in tidally perturbed systems. The resolved radio–SFR slope steepens from 0.57 at 144 MHz to 0.95 at 6 GHz, approaching linearity at high frequencies. This trend is consistent with energy-dependent CRE cooling and transport, with the deviation from linearity most pronounced at low frequencies, where the edge-on line of sight blends midplane and halo CRE populations. These results are robust against thermal contamination, beam smearing, and spectral curvature. Together, our analysis establishes α nth as an observational probe of projected disk-to-halo CRE transport in edge-on galaxies and quantifies how this transport reshapes the frequency dependence of resolved radio–SFR calibrations.
SN - 1538-4357
SN - 0004-637X
ER -