Does Diffuse Circumnuclear Gas around Sgr A* Achieve Collisional Ionization Equilibrium or Remain Non-equilibrium Ionization?
Abstract
The feeding and feedback processes at the vicinity of a supermassive black hole (BH) are essential for our understanding of the connection between supermassive BH and its host galaxy. In this work, we provide a detailed investigation, both observational and theoretical, on the diffuse (~2″-20″, ~0.08-0.8 pc) X-ray emission around Sgr A*. Over two-decade Chandra observations are gathered to obtain highest signal-to-noise to date. We find that, the line center of iron lines of the outer 8″-18″ region, ${\epsilon }_{{\rm{c}}}={6.65}_{-0.03}^{+0.02}\,\mathrm{keV}$ , is comparable to that ( ${\epsilon }_{{\rm{c}}}={6.60}_{-0.03}^{+0.05}\,\mathrm{keV}$ ) of the inner 2″-5″ region. This is somewhat unexpected, since the gas temperature decreases further away from the central BH. Based on a dynamical inflow-outflow model that considers the gas feeding by stellar winds from Wolf-Rayet stars, we calculate the X-ray spectrum based on both the conventional collisional ionization equilibrium (CIE) assumption, and the newly developed non-equilibrium ionization (NEI) assumption. We find that, theoretically gases within ~8″-10″ remain in a CIE state, outside of this radius they will be in the NEI state. A comparison of the properties of ~6.6 keV iron lines between CIE and NEI is addressed. Interestingly, the NEI interpretation of outer region is supported by the Chandra line center ϵ c measurements of this region.
- Publication:
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Research in Astronomy and Astrophysics
- Pub Date:
- August 2023
- DOI:
- 10.1088/1674-4527/acd89f
- Bibcode:
- 2023RAA....23h5005N
- Keywords:
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- X-rays: diffuse background;
- galaxies: active;
- Galaxy: center;
- (galaxies:) quasars: emission lines