VLA Imaging of Atomic Hydrogen-Bearing Ultra-Diffuse Galaxies and the HI Size-Mass Relation

Faculty Sponsor

Luke Leisman


Arts and Sciences


Department of Physics and Astronomy

ORCID Identifier(s)


Document Type

Poster Presentation

Symposium Date

Summer 7-29-2019


This research examines properties of ultra-diffuse galaxies (UDGs), in order to discover more about why and how these types of galaxies exist. UDGs are galaxies that have very little star content for their given radius, so they appear very dim optically but can be observed in radio wavelengths. Our data were taken with the Jansky Very Large Array, which observed radio emission from neutral Hydrogen gas (HI) within the galaxies. To analyze the data, we used CASA, a specific radio astronomy software, to remove interference from the data, calibrate the data, and create images that show the gas distribution in the galaxies. From CASA, we were able to obtain spectra and velocity maps of the galaxies, which we then used to measure the galaxies’ gas mass and motions. Through this process, we determined that the galaxies are rotating and their gas components extend well past their optical components. We often observe that the gas and stellar components are misaligned, indicating that the stars are unreliable in measuring the inclination of these sources. When plotted on the HI size-mass relation, we find that the UDGs have the same average HI surface density as typical galaxies. Therefore, though the stars in UDGs are ultra-diffuse, the HI gas in these galaxies is not. In measuring and comparing the properties of UDGs to typical galaxies, we will have better constraints on galaxy models which will allow us to more fully understand galaxy formation and evolution.

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