Line-of-sight positions of the MC20 and MC50 molecular clouds

Determine the line-of-sight positions of the MC20 and MC50 molecular clouds relative to Sgr A* and the circumnuclear disk.

Background

The MC20 and MC50 clouds lie close to the line of sight toward Sgr A*, the circumnuclear disk, and Sgr A East, making their three-dimensional locations difficult to infer from projected observations. Different dynamical models place them tens to more than one hundred parsecs from the Galactic Center, whereas other observations suggest that they are within roughly ten parsecs.

The paper uses gamma-ray flux compatibility to disfavor the large distances predicted by some models, but does not establish a unique three-dimensional location for either cloud.

References

MC20 and MC50: The positions of MC20 and MC50 have been the subject of high debate for many years, primarily due to projection effects caused by their close proximity to the line of sight of Sgr A$, the CND, and Sgr A East.

— 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”