XMM-Newton Reflection Grating Spectrometer observations of the prototypical starburst galaxy M82

Abstract

We present results from XMM-Newton Reflection Grating Spectrometer observations of the prototypical starburst galaxy M82. These high-resolution spectra represent the best X-ray spectra to date of a starburst galaxy. A complex array of lines from species over a wide range of temperatures is seen, the most prominent being due to Lyman α emission from abundant low-Z elements such as N, O, Ne, Mg and Si. Emission lines from helium-like charge states of the same elements are also seen in emission, as are strong lines from the entire Fe L series. Further, the O VII line complex is resolved and is seen to be consistent with gas in collisional ionization equilibrium. Spectral fitting indicates emission from a large mass of gas with a differential emission measure over a range of temperatures (from ~ 0.2 to ~ 1.6 keV, peaking at ~ 0.7 keV), and evidence for super-solar abundances of several elements is indicated. Spatial analysis of the data indicates that low-energy emission is more extended to the south and east of the nucleus than to the north and west. Higher energy emission is far more centrally concentrated.