The Mass Distribution and Rotation Curve in the Galaxy

TL;DR

This paper reviews methods for determining the Galaxy's mass distribution using rotation curves, comparing dynamical and photometric approaches, and discusses their application to the Milky Way and other spiral galaxies.

Contribution

It provides a detailed overview of dynamical and photometric methods for mass distribution analysis, including the decomposition and direct methods, with applications to the Milky Way and external galaxies.

Findings

Rotation curves are essential for understanding galactic mass distribution.

Dynamical methods include decomposition and direct approaches.

Mass profiles like de Vaucouleurs and exponential disks are discussed.

Abstract

The mass distribution in the Galaxy is determined by dynamical and photometric methods. Rotation curves are the major tool for determining the dynamical mass distribution in the Milky Way and spiral galaxies. The photometric (statistical) method utilizes luminosity profiles from optical and infrared observations, and assumes empirical values of the mass-to-luminosity (M/L) ratio to convert the luminosity to mass. In this chapter the dynamical method is described in detail, and rotation curves and mass distribution in the Milky Way and nearby spiral galaxies are presented. The dynamical method is categorized into two methods: the decomposition method and direct method. The former fits the rotation curve by calculated curve assuming several mass components such as a bulge, disk and halo, and adjust the dynamical parameters of each component. Explanations are given of the mass profiles as the de Vaucouleurs law, exponential disk, and dark halo profiles inferred from numerical simulations. Another method is the direct method, with which the mass distribution can be directly calculated from the data of rotation velocities without employing any mass models. Some results from both methods are presented, and the Galactic structure is discussed in terms of the mass. Rotation curves and mass distributions in external galaxies are also discussed, and the fundamental mass structures are shown to be universal.