Comment on "An X-ray chimney extending hundreds of parsecs above and below the Galactic Centre" (2019, Nature, 567, 34)

Abstract

A recent article "An X-ray chimney extending hundreds of parsecs above and below the Galactic Centre" (2019, Nature, 567, 34) reported the detection of chimney-like X-ray-emitting features above and below the Galactic Center from XMM-Newton observations. We note here that these features were already reported by our Suzaku papers: Nakashima et al. (2013, ApJ, 773, 20, arXiv:1310.4236) for the southern feature and Nakashima et al. (2019, ApJ, in press, arXiv:1903.02571) for the northern feature. In particular, Nakashima et al. (2013) show that the ionization state of the southern feature is not in collisional ionization equilibrium and is most likely in a recombining or over-ionized state, which suggests its origin in the Galactic Center about 0.1 Myr ago.