Modeling CR electron propagation with PIERNIK & CRESP: simulations vs. observational data of NGC891

Abstract

Galactic outflows and extended non-thermal emission due to Comic Ray (CR) electrons have been observed in many edge-on galaxies in the radio range of electromagnetic radiation, allowing us to estimate the strength and vertical structure of the galactic magnetic field. We construct a global model of NGC891 based on the observational characteristics of this galaxy. We assume that on large scales, the dynamics of the magnetized ISM is driven by Cosmic Rays. We apply the coarse-grained momentum finite volume (CGMV), for solving the Fokker–Planck CR transport equation for CR electrons in ”Cosmic Ray Energy SPectrum” (CRESP) module of PIERNIK MHD code to model CR propagation in this galaxy. The overall propagation of cosmic rays is described by the Fokker-Planck equation. The numerical model exhibits magnetic field amplification by CR-driven dynamo. We perform a parameter study of the system by varying the injection spectrum slope, the magnitude and momentum dependence of the CR electron diffusion coefficients and SFR. We take into account the advection, diffusion, and adiabatic changes as well as synchrotron and inverse-Compton losses. The spectrum of synchrotron radiation, polarization maps and spectral index maps reproduce the observed structures of the real edge-on galaxy very well. Comparison of different models suggests harder CR 𝑒 − injection spectra, higher conversion ratios of SN → CR energies (of 10–20%) and diffusion coefficients ∼ 9 × 10 28 cm 2 s − 1 .