Katheryn's Wheel and colliding galaxies

The first thing that you should note about this work (available here) is that it has almost been a decade in the making. The peculiar object, named Katheryn's Wheel, was first discovered in 2005/6 and the authors have been performing follow up observations and digging up archival data on the object ever since. After first being discovered in the optical region, the authors dug up Near Infrared, Mid Infrared, Far Infrared and Radio observations. The authors also pursued follow up spectroscopic observations of specific regions of the object.

I think I should take a step back to give you a look at the bigger picture. Every once in a while, we see galaxies interacting. I'm sure you've heard by now that our own Milky way galaxy and Andromeda are on a path to collide sometime over the next billion years and will end up being one big mess of stars and gas. Similarly, in the past, a lot of galaxies have interacted with our Milky way galaxy. And if we look out into space, we will see many such examples of galaxies interacting. The reason this object is of peculiar interest is because of the spatial morphology of the interaction. Galaxy collisions rarely produce rings (rings where star are forming), because there are constraints on the initial interaction for the end product to be a ring of star formation. Collisional rings are also interesting because the star formation in the ring is manifested because it can help in understanding the density/shock wave that initiated star formation in the ring like structure.

Below is one of the images from the paper. If you neglect the bright star in the south of the picture, you will be able to see a galaxy roughly in the middle of the picture and a circle/oval shape surrounding the central galaxy. There is also a second bright object north west of the central galaxy/ring. The authors speculate that the larger galaxy at the center was disrupted by the smaller galaxy in the top left corner. The orange/red color indicates emission from newly forming stars and you can therefore notice that the central galaxy has almost no orange/red color, meaning that the star formation in the central galaxy was quenched by the collision. This doesn't appear to be the case with the smaller galaxy in the top right corner.

For more pretty pictures or a better understanding of exactly what's happening in this picture, read the paper. The authors are thorough in understanding the star formation rate, the abundances of higher elements and in estimating the time scale of interaction and so on.

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