Clues to the nature of ultra diffuse galaxies from estimated galaxy velocity dispersions

TL;DR

This paper presents a universal method to estimate the velocity dispersions of ultra diffuse galaxies (UDGs) using galaxy scaling relationships, revealing their dark matter dominance and mass range without needing detailed structural data.

Contribution

The study introduces a universal approach to estimate UDG velocity dispersions applicable across various galaxy types, enabling mass and dark matter content analysis without detailed structural information.

Findings

UDGs are dark matter dominated systems.

UDGs span a mass range of $10^{10}$ to $10^{12} M_ ext{sun}$.

The method accurately estimates dispersions for different galaxy types.

Abstract

We describe how to estimate the velocity dispersions of ultra diffuse galaxies, UDGs, using a previously defined galaxy scaling relationship. The method is accurate for the two UDGs with spectroscopically measured dispersions, as well as for ultra compact galaxies, ultra faint galaxies, and stellar systems with little or no dark matter. This universality means that the relationship can be applied without further knowledge or prejudice regarding the structure of a galaxy. We then estimate the velocity dispersions of UDGs drawn from two published samples and examine the distribution of total masses. We find, in agreement with the previous studies of two individual UDGs, that these systems are dark matter dominated systems, and that they span a range of at least $10^{10} < M_{200}/M_\odot < 10^{12} $. These galaxies are not, as an entire class, either all dwarfs or all failed $L_*$ galaxies. Estimates of the velocity dispersions can also help identify interesting subsets of UDGs, such as those that are likely to have the largest mass-to-light ratios, for subsequent spectroscopic study.