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 ∼20 pc and ∼100 pc, respectively. The measured flux $\left({6.8}_{-0.3}^{+0.1}\right)\times {10}^{-10}$erg s⁻¹ cm⁻² in the 4−12 keV band corresponds to a luminosity of $L_{4\text{–}12\mathrm{keV}}=\left({5.9}_{-0.3}^{+0.1}\right)\times {10}^{36}$erg s⁻¹, assuming the GC distance of 8.178 kpc. The average mass-normalized X-ray emissivity of the NSD, $〈L/M〉=\left({5.6}_{-0.7}^{+0.5}\right)\times {10}^{27}$erg s⁻¹ M${}_{\odot }^{-1}$, exceeds the corresponding value for the Galactic ridge by a factor of ${3.3}_{-0.5}^{+0.4}$, 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 3D stellar mass models. Finally, we conclude that the spatial distribution of the X-ray emission from the NSD is consistent with the most recent stellar mass density distribution model within 30%, which suggests that this emission is dominated by unresolved point X-ray sources rather than by diffuse X-ray emission.