Getting to Know Virgo: a Date with Galactic Evolutionary History

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Getting to Know Virgo: a Date with Galactic Evolutionary History

Researchers use phase-space location with hydrogen gas morphology to trace galaxy interactions.

Professor Aeree Chung
Department of Astronomy, Yonsei University

In the continuing quest to understand the internal workings of our cosmos, Dr. Aeree Chung from Yonsei University with other researchers from around the world, attempted to create tools for projecting galaxy trajectories and star formations using only imaging of hydrogen gas. Hydrogen is the most common element in the universe and can be easily visualized using a wide variety of tools. In this case, the researchers focused on HI, which is the chemical symbol for the neutral form of the gas. This is important because it provides a kind of record for where the galaxy has been and what it’s been up to (interactively speaking).

Galaxies, like all physical things, are subject to a wide variety of physical processes. Just as our past helps make up our personality, galaxies’ exposure to tidal effects and something called “ram pressure stripping” (basically the galactic version of getting squeezed and pushed) helps to create a unique signature in the amount of hydrogen available in their disk space. This amount of gas helps determine how many stars get formed, what the shape of the galaxy itself looks like, and can even help predict its trajectory, which, as Dr. Chung notes, “tracing a galaxy’s trajectory from a single snapshot is…difficult, if not impossible.”

Enter the phase-space diagram and ionized cluster gas tracing to diagnose and plot the “stripping status of a galaxy,” or in other words, show the hydrogen lurking around a galactic center. To test the efficacy of their methodology, Dr. Chung and team “focused on Virgo cluster galaxies with high-resolution HI imaging data, which is an excellent indicator of stripping stage.”

The group used phase-space diagrams to categorize thirty-five different galaxies in the Virgo cluster into four different hydrogen morphological types. This data (gleaned from VLA imaging—a survey of Virgo galaxies in atomic gas, or VIVA) showed that specific galaxy shape and hydrogen amounts corresponded to very specific locations near the cluster center. A galaxy’s ‘personality’ could be inferred by its relative position, HI amount and shape. Thus, researchers could piece together its past, a probable future, and take a look at internal formational patterns (like star birth) among the different galactic morphologies. Using these tools, researchers were able to represent “a wealth of information on a galaxy’s evolutionary history.”

Updated in Feb 2018

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Title of original article: A history of HI stripping in Virgo: A phase-space view of VIVA galaxies
Journal: The Astrophysical Journal
DOI: 10.3847/1538-4357/aa6579
Contact corresponding author: Hyein Yoon (; Aeree Chung (