The Imprint of Spiral Arms on the Galactic Rotation Curve

TL;DR

This paper models the Milky Way's rotation curve by incorporating spiral arm features into the stellar density profile, successfully explaining observed discrepancies and predicting a declining rotation curve consistent with observations.

Contribution

It introduces a model that links spiral arm structures to the galactic rotation curve, reconciling stellar and gas dynamics in the Milky Way.

Findings

Spiral arm features align with the density gradient term in the Jeans equation.

Model predicts a declining rotation curve outside the solar circle.

Results match observed rotation curve slopes.

Abstract

We discuss a model for the Milky Way obtained by fitting the observed terminal velocities with the radial acceleration relation. The resulting stellar surface density profile departs from a smooth exponential disk, having bumps and wiggles that correspond to massive spiral arms. These features are used to estimate the term for the logarithmic density gradient in the Jeans equation, which turn out to have exactly the right location and amplitude to reconcile the apparent discrepancy between the stellar rotation curve and that of the interstellar gas. This model also predicts a gradually declining rotation curve outside the solar circle with slope $-1.7\;\mathrm{km}\,\mathrm{s}^{-1}\,\mathrm{kpc}^{-1}$, as subsequently observed.