Suzaku Metal Abundance Patterns in the Outflow Region of M82 and the Importance of Charge Exchange

TL;DR

This study analyzes Suzaku X-ray data of M82, revealing metal abundance patterns in the outflow region and highlighting the significance of charge exchange processes in the central disk's spectral features.

Contribution

It provides the first detailed metal abundance measurements in M82's outflow and emphasizes the role of charge exchange in interpreting spectral lines.

Findings

Charge exchange affects Lyβ/Lyα line ratios in the central region.

Metal abundances in the outflow are consistent with SN II enrichment.

Outflow abundances are more reliable due to lack of charge exchange influence.

Abstract

We performed spectral analysis of Suzaku data of the galactic disk and outflow regions of the starburst galaxy M82. 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 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). Since there is no evidence of charge exchange in 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.