XRISM spectra force revision of M82 free-wind models, revealing Mach 1.7–3.1 motions in starburst core
Idealized hydrodynamic models of M82’s hot wind cannot match XRISM line widths without extra non-thermal broadening, implying supersonic motions inside the starburst that divert supernova energy into magnetic fields and cosmic rays. The finding revises the energy budget available for driving cooler phases of the outflow.
The arXiv paper (Grayson et al. 2026) runs a grid of idealized hydrodynamic free-wind models varying mass and energy loading factors, then generates synthetic XRISM spectra for direct comparison. None reproduce the observed line widths without an added Gaussian broadening component whose origin is interpreted as small-scale turbulence rather than bulk outflow. This single modeling choice rules out pure thermal driving and points to energy partitioning away from heat. The result aligns with earlier Chandra and XMM-Newton limits on M82’s hot-phase temperature but adds the first velocity-dispersion constraint, tightening the allowed parameter space for mass-loading factors below 0.3. It also connects to ALMA and VLA data showing strong magnetic fields and cosmic-ray pressure gradients in the same 200-pc region. Collectively these observations suggest that 30–60 % of supernova energy may be diverted into non-thermal channels before the wind reaches kiloparsec scales. Future XRISM mapping at 10-arcsec resolution and simultaneous MeerKAT polarization observations can test whether the inferred turbulent velocity correlates spatially with synchrotron intensity, providing a direct empirical check on magnetic amplification efficiency.
Grayson et al.: Spatially resolved XRISM spectra will show velocity dispersion dropping below Mach 1.5 outside the central 150 pc within 18 months of Cycle-2 observations.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2607.07782)
- [2]Supporting Source(https://doi.org/10.3847/1538-4357/acd3f0)