Rotation Curve of the Milky Way

TL;DR

This study models the Milky Way's rotation curve using a multi-component approach, revealing tensions between photometric and kinematic data that suggest the need for more complex models of the galaxy's structure.

Contribution

It provides a detailed analysis of the Milky Way's rotation curve with a multi-component mass model and highlights the limitations of simplified axisymmetric assumptions.

Findings

Stellar mass model fits surface density well but poorly matches rotation curve in the inner Galaxy.

Adjusting model parameters improves rotation curve fit but conflicts with baryonic distribution constraints.

Simplified models may be insufficient; more realistic bulge/bar treatments are needed.

Abstract

We investigate the rotation curve of the Milky Way using a multi-component mass model including a stellar disk, a gaseous disk, a bulge/bar component, and a dark-matter halo. The stellar and gas contributions are calibrated using recent observational determinations of the Galactic surface-density distribution, while the dark-matter halo is modelled with standard spherical profiles. We compute the circular-velocity contributions of the different components using a combination of spherical mass reconstruction for the bulge and halo, and thin-disk Hankel-transform methods for the disk and gas components. We first fit the stellar surface-density profile to determine a fiducial bulge-disk decomposition and then use this calibration to predict the Galactic rotation curve. We find that, although the resulting stellar mass model reproduces the observed surface-density profile reasonably well, it does not provide a fully satisfactory description of the rotation-curve data, with the largest discrepancies arising in the inner Galaxy. We then consider an alternative RC-first calibration strategy, in which the bulge and disk parameters are adjusted to improve the kinematic fit. While this significantly improves the agreement with the observed rotation curve, the corresponding stellar surface-density profile becomes inconsistent with the independently inferred baryonic distribution. Our results highlight a tension between photometric and kinematic constraints within simplified axisymmetric models and indicate that a fully consistent description of the Milky Way mass distribution likely requires a more realistic treatment of the bulge/bar structure and of baryonic systematic uncertainties.