A deep X-ray observation of M82 with XMM-Newton

TL;DR

This paper presents a detailed analysis of deep X-ray observations of M82, revealing complex spectral components, spatially varying chemical abundances, and insights into the hot gas and charge exchange processes in the galaxy's outflow.

Contribution

It provides the first detailed spatially resolved X-ray spectral analysis of M82's outflow, identifying multiple emission components and abundance variations.

Findings

Identification of three main spectral components in M82's X-ray emission

Detection of spatial variations in chemical abundances within the outflow

Observation of lower Oxygen abundance compared to stellar atmospheres

Abstract

We report on the analysis of a deep (100 ks) observation of the starburst galaxy M82 with the EPIC and RGS instruments on board the X-ray telescope XMM-Newton. The broad-band (0.5-10 keV) emission is due to at least three spectral components: i) continuum emission from point sources; ii) thermal plasma emission from hot gas; iii) charge exchange emission from neutral metals (Mg and Si). The plasma emission has a double-peaked differential emission measure, with the peaks at ~0.5 keV and ~7 keV. Spatially resolved spectroscopy has shown that the chemical absolute abundances are not uniformly distributed in the outflow, but are larger in the outskirts and smaller close to the galaxy centre. The abundance ratios also show spatial variations. The X-ray derived Oxygen abundance is lower than that measured in the atmospheres of red supergiant stars, leading to the hypothesis that a significant fraction of Oxygen ions have already cooled off and no longer emit at energies > ~0.5 keV.