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

TL;DR

This study characterizes the X-ray emission of the Nuclear Stellar Disk in the Milky Way's center using SRG/ART-XC data, revealing its spatial structure, luminosity, and relation to stellar mass distribution, indicating unresolved point sources dominate.

Contribution

First detailed analysis of the NSD's X-ray emission with wide-field observations, providing spatial, luminosity, and mass-normalized emissivity measurements, and comparing to stellar mass models.

Findings

X-ray emission is dominated by the NSD aligned with the Galactic plane.

Measured X-ray luminosity of the NSD is approximately 6 x 10^36 erg/s.

X-ray emissivity exceeds the Galactic ridge by a factor of 3.3.

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 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.