eROSITA narrowband maps at the energies of soft X-ray emission lines

Vol. 689
5. Galactic structure, stellar clusters and populations

eROSITA narrowband maps at the energies of soft X-ray emission lines

The promise of the eROSITA mission is demonstrated in dramatic fashion with the publication of these soft X-ray emission line half-sky maps. Elucidating the hot phase of the interstellar medium requires observations in the soft X-ray band, below about 2 keV. The mission's most important innovation is its spectral resolution, which permits spectrophotometric mapping of the sky in the emission lines that dominate the cooling of the medium, principally during high-ionization stages of oxygen, in addition to the broadband continuum emission. This paper presents maps of the third and fourth Galactic quadrants, which show strong variations in the O VII/O VI line ratio (a proxy measure of temperature) along the Galactic plane and an asymmetry on the order of ten percent between the northern and southern hemispheres on scales of tens of degrees. Such structuring will be essential information for modeling the effects of stellar feedback, especially superbubbles, and the imbedding of molecular clouds within this medium.