Charge Exchange X-ray Emission of M82: K{\alpha} triplets of O VII, Ne
  IX, and Mg XI
  Starburst galaxies are primary feedback sources of mechanical energy and
metals, which are generally measured from associated X-ray emission lines
assuming that they are from the thermal emission of the outflowing hot gas.
Such line emission, however, can also arise from the charge exchange X-ray
emission (CXE) between highly ionized ions and neutral species. To understand
the feedback of energy and metals, it is crucial to determine the origin of the
X-ray emission lines and to distinguish the contributions from the CXE and the
thermal emission. The origin of the lines can be diagnosed by the K{\alpha}
triplets of He-like ions, because the CXE favors the inter-combination and
forbidden lines, while the thermal emission favors the resonance line. We
analyze the triplets of O VII, Ne IX, and Mg XI observed in the XMM- Newton
reflection grating spectra of the starburst galaxy M82. The flux contribution
of the CXE is 90%, 50%, and 30% to the O VII, Ne IX, and Mg XI triplet,
respectively. Averaged over all the three triplets, the contribution of the CXE
is \sim 50% of the total observed triplet flux. To correctly understand the hot
outflow of starburst galaxies, it is necessary to include the CXE. Based on the
measured CXE contributions to the O VII, Ne IX, and Mg XI triplets, we estimate
the relative abundances of O, Ne, and Mg of the outflow and find they are
similar to the solar ratios.
