X-ray emission of the Nuclear Stellar Disk as seen by SRG/ART-XC

Abstract: The Nuclear Stellar Disk (NSD), together with the Nuclear Stellar Cluster and the supermassive black hole Sgr A*, forms the central region of the Milky Way. Galactic X-ray background emission is known to be associated with the old stellar population, predominantly produced by accreting white dwarfs. In this work we characterize the X-ray emission of the Galactic Center (GC) region using wide-field observations with the ART-XC telescope on board the SRG observatory in the 4-12 keV energy band. Our analysis demonstrates that the X-ray emission of the GC at a spatial scale of a few hundred parsecs is dominated by the regularly shaped NSD aligned in the Galactic plane, and characterized by latitudinal and longitudinal scale heights of approximately 20 pc and approximately 100 pc, respectively. The measured flux, 6.8 (+0.1, -0.3) x 10^-10 erg/s/cm^2 in the 4-12 keV band, corresponds to a luminosity of 5.9 (+0.1, -0.3) x 10^36 erg/s, assuming the GC distance of 8.178 kpc. The average mass-normalized X-ray emissivity of the NSD, 5.6 (+0.5, -0.7) x 10^27 erg/s/M_sun, exceeds the corresponding value of the Galactic ridge by a factor of 3.3 (+0.4, -0.5), confirming other studies. We also perform a deprojection of the observed NSD surface brightness distribution in order to construct a three-dimensional X-ray luminosity density model, which can be directly compared to the existing three-dimensional stellar mass models. The emissivity of the NSD as a function of distance to Sgr A* reveals a centrally concentrated maximum, indicating an enhanced radiative output per unit stellar mass in the inner NSD region. Finally, we conclude that the observed spatial properties of the NSD are fully consistent with the stellar mass density distribution, leaving only a small room for a possible diffuse component.