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

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 $L_{\ast }$ 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.

4 pages, accepted for publication in MNRAS Letters (typographical error in Equation 1 corrected)

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• Detection of a Large Population of Ultra Diffuse Galaxies in Massive Galaxy Clusters: Abell S1063 and Abell 2744
• On the Properties of Spectroscopically-Confirmed Ultra-Diffuse Galaxies Across Environment
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• A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE).XIII. The role of ram-pressure stripping in transforming the diffuse and ultra-diffuse galaxies in the Virgo cluster
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• Keck Spectroscopy of the Coma Cluster Ultra-Diffuse Galaxy Y358: Dynamical Mass in a Wider Context
• Constraining the dark matter halo mass of isolated low-surface-brightness galaxies
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• HIPASS study of southern ultradiffuse galaxies and low surface brightness galaxies
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