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

TL;DR

This paper critiques a recent claim of X-ray chimney features near the Galactic Center, highlighting prior observations by the authors that identified these features and their ionization states, suggesting an earlier origin.

Contribution

It clarifies that the X-ray chimney features were previously reported by the authors, providing context and details about their ionization states and origins.

Findings

Features were previously reported by Nakashima et al. (2013, 2019).

Southern feature is in a recombining or over-ionized state.

Features likely originated from the Galactic Center about 0.1 Myr ago.

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.