Magnetically Confined Interstellar Hot Plasma in the Nuclear Bulge of our Galaxy

TL;DR

This study investigates the origin of the hot diffuse X-ray emission in the Galactic center, suggesting it is magnetically confined interstellar plasma rather than unresolved point sources, supported by spatial distribution and magnetic field observations.

Contribution

It provides evidence that the hot plasma in the Galactic center is magnetically confined interstellar gas, not solely from stellar sources, and measures the scale height of the Nuclear stellar disk.

Findings

Hot plasma is likely magnetically confined, reducing energy requirements.

Spatial distribution of X-ray emission does not match old stellar population.

Confirmed large-scale toroidal magnetic field in the Galactic center region.

Abstract

The origin of the Galactic center diffuse X-ray emission (GCDX) is still under intense investigation. In particular, the interpretation of the hot (kT ~ 7 keV) component of the GCDX, characterised by the strong Fe 6.7 keV line emission, has been contentious. If the hot component originates from a truly diffuse interstellar plasma, not a collection of unresolved point sources, such plasma cannot be gravitationally bound, and its regeneration would require a huge amount of energy. Here we show that the spatial distribution of the GCDX does NOT correlate with the number density distribution of an old stellar population traced by near-infrared light, strongly suggesting a significant contribution of the diffuse interstellar plasma. Contributions of the old stellar population to the GCDX are implied to be about 50 % and 20 % in the Nuclear stellar disk and Nuclear star cluster, respectively. For the Nuclear stellar disk, a scale height of 0.32 +- 0.02 deg is obtained for the first time from the stellar number density profiles. We also show the results of the extended near-infrared polarimetric observations in the central 3 deg * 2 deg region of our Galaxy, and confirm that the GCDX region is permeated by a large scale, toroidal magnetic field as previously claimed. Together with observed magnetic field strengths close to energy equipartition, the hot plasma could be magnetically confined, reducing the amount of energy required to sustain it.