SALT Digs Up Hot Gas Above Galaxy M83

Aug 30, 2017

Galaxies contain gas at different temperatures and states. These so-called phases range from cold, molecular gas found in dense clouds to hot, ionized plasma that fills most of the volume of a galaxy. Understanding how much of this gas is there, where it is, and whether and how it is moving is important for understanding how a galaxy formed and how it is evolving. By studying the location and dynamics of different phases of the interstellar gas, we can patch together a model for the life of that galaxy.

UW grad student Erin Boettcher, working with Professors Ellen Zweibel and Jay Gallagher, used the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT) to study the dynamics of gas that is about 1000 degree Kelvin hot, and ionized. What special about this gas is that it does not reside in the Galaxy itseld, but sitting above and below the disk. They found from the spectra they took that this so-called extra-planar diffuse ionized gas (eDIG) is supported by turbulence, and that it is likely in a state that is not static (that is, it is not simply staying put) but also not collapsing or exploding. This is one of the first times researchers were able to study this gas in galaxies that are seen face-on, as can be seen in the beautiful image of M83 below.

Messier 83. Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

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