Major structures of the inner Galaxy delineated by 6.7-GHz methanol masers

TL;DR

This paper uses 6.7-GHz methanol masers to map the inner Galaxy's structure, revealing features like spiral arms and a long thin bar, and comparing observations with gas dynamic models.

Contribution

It provides new insights into the Galaxy's inner structure by analyzing methanol maser distributions and their relation to spiral arms and the Galactic bar.

Findings

Identification of density enhancements indicating star formation regions.

Support for a long thin Galactic bar at 45 degrees orientation.

Detection of the 3-kpc arm structure and its relation to the bar's corotation resonance.

Abstract

We explore the longitude-velocity distribution of 6.7-GHz methanol masers in the context of the inner structure of our Galaxy. We analyse the correlation in velocities within this distribution and identify density enhancements indicating large-scale regions of enhanced star formation. These are interpreted as the starting points of the spiral arms and the interaction of the Galactic bar with the 3-kpc arms. The methanol masers support the presence of a long thin bar with a 45 degree orientation. Signatures of the full 3-kpc arm structure are seen, including a prominent tangent at approximately -22 degrees Galactic longitude. We compare this distribution with existing models of the gas dynamics of our Galaxy. The 3-kpc arm structure appears likely to correspond to the radius of corotation resonance of the bar, with the bar on its inner surface and the starting points of the spiral arms on its outer surface.