Ne x X-ray emission due to charge exchange in M82

• Published in: Monthly notices of the Royal Astronomical Society 2016-06, Vol.458 (4), p.3554-3560
• Main Authors: Cumbee, R. S., Liu, L., Lyons, D., Schultz, D. R., Stancil, P. C., Wang, J. G., Ali, R.
• Format: Article
• Language: English
• Subjects: Astrophysics; Charge exchange; Emissions; Kinetic energy; Kinetics; Low energy; Monte Carlo methods; Monte Carlo simulation; Orbitals; Spectrum analysis; Star & galaxy formation; Symbols; Trajectories; X-ray astronomy; X-rays
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw527

Recent X-ray observations of star-forming galaxies such as M82 have shown the Ly β/Ly α line ratio of Ne x to be in excess of predictions for thermal electron impact excitation. Here, we demonstrate that the observed line ratio may be due to charge exchange and can be used to constrain the ion kinetic energy to be ≲ 500 eV/u. This is accomplished by computing spectra and line ratios via a range of theoretical methods and comparing these to experiments with He over astrophysically relevant collision energies. The charge exchange emission spectra calculations were performed for Ne10++ H and Ne10++ He using widely applied approaches including the atomic orbital close coupling, classical trajectory Monte Carlo, and multichannel Landau–Zener (MCLZ) methods. A comparison of the results from these methods indicates that for the considered energy range and neutrals (H, He) the so-called low-energy ℓ-distribution MCLZ method provides the most likely reliable predictions.