Diffuse X-ray Emission in the Sagittarius C Complex

Abstract

The Sagittarius C (Sgr C) complex, located on the western edge of the Central Molecular Zone (CMZ), hosts a mixture of star-forming and non-thermal activity whose X-ray properties remain poorly understood. Using deep archival Chandra and XMM-Newton observations, we resolve the diffuse X-ray emission in Sgr C into two components: an H II region coincident with the radio peak and a brighter diffuse feature located to its southwest. Spatially resolved spectroscopy reveals the presence of a soft (kT <= 1 keV) plasma with metal abundances consistent with the elevated metallicity expected in the CMZ in both regions, along with a harder (~ 8 keV) thermal component within the H II region. The observed diffuse X-ray emission and its association with an expanding [C II] shell suggest that the hot gas may originate from a young supernova remnant (SNR) embedded in the H II region. Under this interpretation, the inferred shock velocity (~ 800 km/s) and SNR age (>= 1.7 kyr) are consistent with a core-collapse SNR in the Galactic Center. These results reveal Sgr C as a potential host of a SNR and highlight the complex interplay between massive-star feedback, magnetic fields, and molecular gas in the CMZ.

Figures (9)

• Figure 1: Exposure- and vignetting-corrected X-ray flux images of the Sgr C region. Left: Chandra flux image in the 1--4 keV band. For visualization purpose, the image has been smoothed with a gaussian kernel of 11 $\times$ 11 pixels (5.5 x 5.5 ). Right: XMM-Newton flux image in the 0.5-4 keV band. The dashed white circle in both images shows the location and approximate periphery of the Sgr C H ii region, while the cyan circles show the newly-discovered feature -- the bright "Blob". In the Chandra image, we mark the edges of the X-ray emission with yellow dashed lines, which show an excellent spatial coincidence with the edge of the adjacent distribution of foreground cold dust, as shown in Figure \ref{['fig:infrared']}.
• Figure 2: A detailed XMM-Newton view of the “Channel,” a diffuse X-ray structure extending $\sim$26 pc northward.
• Figure 3: Multi-wavelength view of Sgr C. Left: Radio and X-ray overlay of Sgr C. The radio emission of MeerKAT is shown in red, while the cyan shows the 0.5--2 keV XMM-Newton X-ray emission. The 3 dotted green circles denote the selected local background regions. The white dashed circle encloses the H ii region, while the orange dashed circle marks the Blob region. Right: the CMZ in [C ii] Survey image of the $-41$ km s$^{-1}$ velocity channel observed using SOFIA/upGREAT Riquelme2025. The H ii region is marked by a white dashed circle.
• Figure 4: Adaptively-binned XMM-Newton flux maps and hardness ratio map. The dashed circles mark the locations of the H ii region and the Blob. The signal-to-noise ratio for each bin is set to be higher than 10.
• Figure 5: XMM-Newton spectra of the Sgr C H ii region (left panels) and the Blob region (right panels). MOS1 in black, MOS2 in red and PN in green.Top Left: H ii spectrum in 5--8 keV fitted using absorbed vapec model; Top Right: Blob spectrum in 5--8 keV fitted with absorbed vapec model; Bottom Left: Best-fit tbabs*(vapec+apec) model for HII region; Bottom Right: Best-fit tbabs*(vapec+crefl16) model for Blob region; In bottom panels, the dotted lines show the individual components of the best-fit model.