Diffuse X-Ray Sky in the Galactic Center

Abstract

The Galactic Diffuse X-ray Emission (GDXE) in the Milky Way Galaxy is spatially and spectrally decomposed into the Galactic Center X-ray Emission (GCXE), the Galactic Ridge X-ray Emission (GRXE) and the Galactic Bulge X-ray Emission (GBXE). The X-ray spectra of the GDXE are characterized by the strong K-shell lines of the highly ionized atoms, the brightest are the K-shell transition (principal quantum number transition of $n=2\to 1$) of neutral iron (SXV-He$\alpha$), He-like iron (FeXXV-He$\alpha$) and He-like sulfur (SXV-He$\alpha$) lines. Accordingly, the GDXE is composed of a high-temperature plasma of $\sim$7 keV (HTP) and a low-temperature plasma of $\sim$1 keV (LTP), which emit the FeXXV-He$\alpha$ and SXV-He$\alpha$ lines, respectively. The FeI-K$\alpha$ line is emitted from nearly neutral irons, and hence the third component of the GDXE is a Cool Gas (CG). The FeI-K$\alpha$ distribution in the GCXE region is clumpy (FeI-K$\alpha$ clump), associated with giant molecular cloud (MC) complexes, Sagittarius A, B, C, D and E, in the central molecular zone. The origin of the FeI-K$\alpha$ clumps is the fluorescence and Thomson scattering from the MCs irradiated by past big flares of the super massive black hole Sagittarius A${}^{\ast }$. The scale heights and equivalent widths of the FeI-K$\alpha$, FeXXV-He$\alpha$, and FeXXVI-Ly$\alpha$ ($n=2\to 1$ transition of H-like iron) lines are different among the GCXE, GBXE and GRXE. Therefore the structure and origin are separately examined. This paper overviews the research history and the present understandings of the GDXE, in particular focus on the origin of the HTP and CG in the GCXE.

46 pages, 9 figures, 15 tables, accepted to PASJ, but some figures are missing from the original PASJ paper (24 figures) due to the memory limit of figures

References in corpus (22)

• Giant Gamma-ray Bubbles from Fermi-LAT: AGN Activity or Bipolar Galactic Wind?
• Discrete sources as the origin of the Galactic X-ray ridge emission
• Chemical Abundances of Luminous Cool Stars in the Galactic Center from High-Resolution Infrared Spectroscopy
• X-ray hiccups from SgrA* observed by XMM-Newton. The second brightest flare and three moderate flares caught in half a day
• The Origin of Diffuse X-ray and $\gamma$-ray Emission from the Galactic Center Region: Cosmic Ray Particles
• The Interplay between Star Formation and the Nuclear Environment of our Galaxy: Deep X-ray Observations of the Galactic Center Arches and Quintuplet Clusters
• ATLASGAL - Kinematic distances and the dense gas mass distribution of the inner Galaxy
• Discovery of Variable Iron Fluorescence from Reflection Nebulae in the Galactic Center
• Exploring a SNR/Molecular Cloud Association Within HESS J1745-303
• Nonthermal X-rays from low-energy cosmic rays: Application to the 6.4 keV line emission from the Arches cluster region
• A Catalog of Diffuse X-ray-Emitting Features within 20 pc of Sgr A*: Twenty Pulsar Wind Nebulae?
• NuSTAR study of Hard X-Ray Morphology and Spectroscopy of PWN G21.5-0.9
• Resolving the Galactic X-ray background
• Spatial distribution and galactic model parameters of cataclysmic variables
• Discovery of Recombining Plasma in the Supernova Remnant 3C 391
• Origin of the Galactic Diffuse X-ray Emission: Iron K-shell Line Diagnostics
• Map of the Galaxy in the 6.7 keV emission line
• On the contribution of point sources to the Galactic ridge X-ray emission
• Low-luminosity X-ray sources and the Galactic ridge X-ray emission
• Variation of the X-ray non-thermal emission in the Arches cloud
• An Imaging and Spectral Study of Ten X-Ray Filaments around the Galactic Center
• X-ray Filament with a Strong 6.7 keV Line in the Galactic Center Region