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Abstract The 3D structure of the Milky Way’s central molecular zone (CMZ) informs our understanding of star formation cycles, black hole accretion, and the evolution of galactic nuclei. However, a comprehensive 3D model has remained elusive, as no singular data set nor theory contains the requisite information to describe the orbital motion of the gas. We implement a Bayesian framework to flexibly combine data sets across the electromagnetic spectrum for molecular clouds in our CMZ catalog. We develop near/far metrics for each data set, including dust extinction, absorption, stellar densities, X-ray echoes, and proper motions; and report a posterior positional probability density function (PPDF) for each cloud. We then use the posterior PPDF distributions for all CMZ clouds to search for a best-fittingx2orbit. We find that no single orbit is a perfect fit, but the structure can overall be represented by nestedx2orbits, with major axes ranging from about 72 < a < 146 pc. We also present projected line-of-sight distance estimates for all 31 clouds in the catalog. Our results highlight asymmetries along the line of sight, with most clouds lying on the near side of the Galactic center, and agree overall with current near/far assumptions for most CMZ clouds, including those in the Sgr A region, which may be much closer to the center. We conclude that the CMZ can be well-described byx2orbital families and that the overall gas distribution is more complex than a single closed or open elliptical orbit.
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This content will become publicly available on February 1, 2027
Unveiling the 3D structure of the central molecular zone from stellar kinematics and photometry: The 50 and 20 km/s clouds
Context. The central molecular zone (CMZ), surrounding the Galactic centre, is the largest reservoir of dense molecular gas in the Galaxy. Despite its relative proximity, the 3D structure of the CMZ remains poorly constrained, primarily due to projection effects. Aims. We aim to constrain the line-of-sight location of two molecular clouds in the CMZ - the 50 and 20 km/s clouds - and to investigate their possible physical connection using stellar kinematics and photometry. This study serves as a pilot for future applications across the full CMZ. Methods. We estimated the line-of-sight position of the clouds by analysing stellar kinematics, stellar densities, and stellar populations towards the cloud regions and a control field. Results. We find an absence of westward moving stars in the cloud regions, which indicates that they lie on the near side of the CMZ. This interpretation is supported by the stellar density distributions. The similar behaviour observed in the two clouds, as well as in the region between them (the ridge), suggests that they are located at comparable distances and are physically linked. We also identified an intermediate-age stellar population (2-7 Gyr) in both regions, consistent with that observed on the near side of the CMZ. We estimated the line-of-sight distances at which the clouds and the ridge become kinematically detectable (i.e. where the proper motion component parallel to the Galactic plane differs from that of the control field at the 3σ level) by converting their measured proper motions parallel to the Galactic plane using a theoretical model of the stellar distribution. We find that the 50 and 20 km/s clouds are located at 43 ± 8 pc and 56 ± 11 pc from Sgr A*, respectively, and that the ridge lies at 56 ± 11 pc; this supports the idea that the clouds are physically connected through the ridge.
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- PAR ID:
- 10680335
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Astronomy and Astrophysics
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 706
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- A18
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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