Suzaku Metal Abundance Patterns in the Outflow Region of M 82 and the Importance of Charge Exchange

Abstract

We performed spectral analysis of Suzaku data of the galactic disk and outflow regions of the starburst galaxy M 82. Thermal modeling of the central disk regions requires at least three temperature components. The Ly $\beta $ line fluxes of O VIII and Ne X exceed those expected from a plasma in collisional ionization equilibrium. The ratios of the Ly $\beta/$ Ly $\alpha$ lines for O VIII and Ne X are higher than those of collisional ionization equilibrium, which may be caused by the process of charge exchange. In the outflow wind region, the spectra are well reproduced with two-temperature thermal models, and we have derived the metal abundances of O, Ne, Mg, and Fe in the outflow. The ratios of O $/$ Fe, Ne $/$ Fe, and Mg $/$ Fe are about 2, 3, and 2, respectively, relative to the solar value determined by Lodders (2003, ApJ, 591, 1220). Since there is no evidence of charge exchange in the outflow region, the metal abundances should be more reliable than those in the central region. This abundance pattern indicates that starburst activity enriches the outflow through SN II metal ejection into intergalactic space.