Observing gas dynamics in distant galaxies

Astronomy has come a long way since Tycho Brahe's time, when astronomers used to spend nights tiring their eyes looking through the eyepiece of a refractor telescope. It has evolved immensely on the 20th century, and in particular the use of CCDs for astronomical research was a major revolution. Now we can quantify the incoming light of objects in the sky with an unprecedented level of detail.

The one case I want to discuss here is the recent invention of Integral Field Units, or IFUs. One of the main ways that astronomers study stars and galaxies is through the use of spectroscopy - that is, separating the incoming light into its different wavelengths, more or less like putting a prism at the end of the telescope.


Image courtesy of amateurspectroscopy.com

Through the use of spectroscopy, one can actually determine the elements that compose the observed object, since each group of lines is a unique signature of that element. Not only that, but we can study how fast the element is moving with respect to us (as, for example, in the case of redshifts). The observed dynamics can provide you with valuable information to understand how an object was formed.

Now, IFUs are even more sophisticated. By dividing the image in small pixels and getting spectra for each one, you can understand how the whole object is moving! For example, a number of astronomers study how hydrogen gas is moving around galaxies far, far away, and that tells them whether that gas is rotating around some center. For you to have an idea, each pixel has an angular size of less than a football field on the moon! Since the galaxy is far, far away (easily more than a billion light-years away, in fact), we can't see a football field, but rather each pixel in the IFU gives us spectral information of a region approximately 1,000 light-years across.

Still, that resolution is enough to tell us a great deal about the galaxy, in what might resemble a 3D picture. How fast is it rotating? Are there internal kinematics that differ from the dynamics of the galaxy as a whole? Is the movement of the gas ordered at all, or is it random? Or maybe through studying the motion of the gas we can realize that object is the result of two galaxies that collided some millions of years ago! This is all very important when we try to understand one simple question that has not yet found a satisfactory answer: how do galaxies (and our own Galaxy, for that matter) came to be what they are?

For more information, check out James Larkin's talk in mp3 or pdf format.

This post had a big help from Karín.