Dynamics of the Disks of Nearby Galaxies

TL;DR

This paper discusses methods to infer galactic disk dynamics from imaging and spectroscopy, highlighting the degeneracy in rotation curve decomposition and using stability and density wave diagnostics to determine mass distribution, revealing baryon dominance and high mass-to-light ratios in certain galaxies.

Contribution

It introduces combined diagnostic techniques to better constrain galactic disk mass distributions and demonstrates their application to various galaxy types, including low surface brightness galaxies.

Findings

Inner galaxy regions are baryon-dominated.

Unexpectedly high mass-to-light ratios in low surface brightness galaxies.

Diagnostics suggest bottom-heavy initial mass functions.

Abstract

I describe how the dynamics of galactic disks can be inferred by imaging and spectroscopy. Next I demonstrate that the decomposition of the rotation curves of spiral galaxies into the contributions by the various components of the galaxies is highly degenerate. Constraints on the decomposition can be found by considering implications for the dynamics of the galactic disks. An important diagnostic is the Toomre Q stability parameter which controls the stability of a galactic disk against local Jeans collapse. I also show how the density wave theory of galactic spiral arms can be employed to constrain the mass of a galactic disk. Applying both diagnostics to the example of NGC 2985 and discussing also the implied mass-to-light ratio I demonstrate that the inner parts of the galaxy, where the optical disk resides, are dominated by baryons. When I apply this method to the disks of low surface brightness galaxies, I find unexpectedly high mass-to light ratios. These could be explained by population synthesis models which assume a bottom heavy initial mass function similar to the recently proposed `integrated galactic initial mass function'.