Reconciling 3D Models for the Central 10 parsecs of the Milky Way

TL;DR

This paper develops a new 3D model of the Milky Way's central 10 parsecs, reconciling previous observations and kinematic data to clarify the spatial arrangement of gas clouds and structures near Sgr A*.

Contribution

It introduces an alternative 3D model placing key gas clouds over 10 pc in front of Sgr A*, challenging prior models and interpretations of their connections.

Findings

The 20 km/s and 50 km/s clouds are over 10 pc in front of Sgr A*.

The new model aligns with radio observations and gas kinematics.

Connections between clouds and the circumnuclear disk are tenuous.

Abstract

The construction of an accurate 3D model of the Milky Way center is necessary to understand inflow processes that drive its overall evolution, and to compare our Galactic nucleus to other galaxies' nuclei. A main point of contention is the line-of-sight location of sources observed toward the central 10 pc of the Galaxy, including recent star formation (the Sgr A East supernova remnant and Sgr A HII regions) and copious gas (the 50 and 20 km/s molecular clouds, the Circumnuclear Disk, and the Sgr A West ionized "minispiral" that encircles the central supermassive black hole, Sgr A*). Some models place all of these structures within a radius of 5 pc from Sgr A*, while others place the 20 and 50 km/s clouds at a distance of at least 30 - 50 pc away from Sgr A* along the line of sight. We present new radio and millimeter observations of the molecular gas toward the central ~10 pc, from which we have constructed an alternative 3D model that is consistent with both prior radio observations and orbital gas kinematics. Our model places the 20 km/s cloud, 50 km/s cloud, and Sgr A East more than 10 pc in front of Sgr A*. While this model does not conclusively rule out a connection between the 50 and 20 km/s clouds and the circumnuclear disk, we argue that prior evidence for these connections is tenuous, especially given the complex spatial and kinematic overlap of structures along the line of sight.