Three-dimensional geometry and dynamics of the central molecular zone

Characterize the three-dimensional geometry, orientation, individual cloud positions, and dynamics of the Milky Way’s central molecular zone, which remain unresolved despite extensive observational study.

Background

The central molecular zone contains dense molecular clouds whose spatial arrangement is essential for interpreting the Galactic Center ridge gamma-ray emission and for modeling the cosmic-ray density distribution. The paper adopts a three-dimensional gas model based on observational tracers, but emphasizes that the actual gas geometry and dynamics are not uniquely established.

Resolving this issue would improve the interpretation of gamma-ray emissivities, cosmic-ray gradients, and the comparison among competing dynamical descriptions of the central molecular zone.

References

Despite numerous studies, the three-dimensional geometry of the CMZ remains debated: although the gas in the CMZ is generally thought to be organized into a ring-like structure, its orientation, shape, individual cloud positions, and dynamics remain unclear.

— Evidence for a spectral steepening of the gamma-ray emission from the Galactic Center ridge  (2608.25946 - Acharyya et al., 26 Aug 2026) in Section 1, Introduction

Sgr C: This cloud has been identified as connected to the contiguous stream associated with the MC20/50 clouds by several studies but its position is highly debated.

— Evidence for a spectral steepening of the gamma-ray emission from the Galactic Center ridge  (2608.25946 - Acharyya et al., 26 Aug 2026) in Section 6.4, “On the line-of-sight distance of CMZ molecular clouds”

G1.3: Unlike the other structures, the G1.3 complex extends over a large distance interval along the line-of-sight. Located on the edge of the CMZ in projection, its possible connection with it is still debated.

— Evidence for a spectral steepening of the gamma-ray emission from the Galactic Center ridge  (2608.25946 - Acharyya et al., 26 Aug 2026) in Section 6.4, “On the line-of-sight distance of CMZ molecular clouds”