Prospects of 3D mapping of the Galactic Centre clouds with X-ray polarimetry

Abstract

Despite past panchromatic observations of the innermost part of the Milky Way, the overall structure of the Galactic Centre (GC) remains enigmatic in terms of geometry. In this paper, we aim to show how polarimetry can probe the three-dimensional position of the molecular material in the central ~100 pc of the GC. We investigate a model where the central supermassive black hole Sgr A* is radiatively coupled to a fragmented circumnuclear disc (CND), an elliptical twisted ring representative of the central molecular zone (CMZ), and the two main, bright molecular clouds Sgr B2 and Sgr C. 8 -- 35 keV integrated polarization mapping reveals that Sgr B2 and Sgr C, situated at the two sides of the CMZ, present the highest polarization degrees (66.5 and 47.8 per cent respectively), both associated with a polarization position angle psi = 90deg (normal to the scattering plane). The CND shows a lower polarization degree, 1.0 per cent with psi = -20.5deg, tracing the inclination of the CND with respect to the Galactic plane. The CMZ polarization is spatially variable. We also consider a range of spatial locations for Sgr A* and the reprocessing media, and investigate how the modeled three-dimensional geometry influences the resulting GC polarization. The two reflection nebulae are found to always produce high polarization degrees (>> 10 per cent). We show that a 500 ks observation with a broadband polarimeter could constrain the location and the morphology of the scattering material with respect to the emitting source, revealing the past activity of Sgr A*.

8 pages, 4 Figures, 4 Tables, accepted for publication in MNRAS

References in corpus (7)

• Trigonometric Parallaxes of Massive Star Forming Regions: VI. Galactic Structure, Fundamental Parameters and Non-Circular Motions
• Star Formation in the Central 400 pc of the Milky Way: Evidence for a Population of Massive YSOs
• X-ray hiccups from SgrA* observed by XMM-Newton. The second brightest flare and three moderate flares caught in half a day
• NuSTAR detection of high-energy X-ray emission and rapid variability from Sagittarius A* flares
• Spectral imaging of the Sagittarius B2 region in multiple 3-mm molecular lines with the Mopra telescope
• GBT Multiwavelength Survey of the Galactic Center Region
• Massive Star Formation in the Molecular Ring Orbiting the Black Hole at the Galactic Center

Cited by in corpus (7)

• X-ray polarization evidence for a 200 years-old flare of Sgr A${}^{\ast }$
• Unveiling the physics behind the spectral variations of "changing-look" quasars with optical polarimetry
• Reflection nebulae in the Galactic Center: the case for soft X-ray imaging polarimetry
• 25 years of XMM-Newton observations of the Sgr A complex: 3D distribution and internal structure of the clouds
• Prospects for the polarimetric mapping of the Sgr A molecular cloud complex with IXPE
• Prospects for IXPE and eXTP polarimetric archaeology of the reflection nebulae in the Galactic center
• Cosmic rays, gas and dust in the Central Molecular Zone I -- $X_{CO}$ factors, cosmic-ray densities and dust opacities