On the soft X-ray emission of M82

TL;DR

This study analyzes the spatial correlation of soft X-ray and Hα emissions in M82's outflow, revealing complex spectral features and proposing multiple explanations for the observed O VII triplet variations.

Contribution

It provides the first detailed spatial analysis of soft X-ray and Hα emissions in M82's outflow, highlighting the dominance of forbidden lines and exploring potential physical mechanisms.

Findings

Soft X-ray and Hα emissions are tightly correlated across various scales.

The O VII triplet is dominated by the forbidden line, contrary to thermal predictions.

Spatial variations in the O VII triplet suggest complex physical processes.

Abstract

We present a spatial analysis of the soft X-ray and H{\alpha} emissions from the outflow of the starburst galaxy M82. We find that the two emissions are tightly correlated on various scales. The O VII triplet of M82, as resolved by X-ray grating observations of XMM-Newton, is dominated by the forbidden line, inconsistent with the thermal prediction. The O VII triplet also shows some spatial variations. We discuss three possible explanations for the observed O VII triplet, including the charge exchange at interfaces between the hot outflow and neutral cool gas, a collisional non-equilibrium-ionization recombining plasma, and resonance scattering.