It’s difficult in my opinion to choose a favourite galaxy, there’s just so much variation and unique features. But I think this one has to be at least in my least top 3, and is definitely my favourite active galaxy!

Today let’s explore the Teacup AGN, sometimes just called “The Teacup”. We’ll be looking at what type of galaxy it is, it’s morphological characteristics, and the interesting green tail.

Basic Facts

The teacup galaxy is an active galaxy located in my favourite constellation Boötes, which may or may not have contributed to my love for this galaxy. You may have noticed I also keep calling it an “active galaxy”. The Teacup is a type of active galaxy known as a type 2 quasar, meaning it is part of an elite class of galaxies with extremely powerful and luminous centers, powered by accretion of matter into the Supermassive black hole.

Quasars and blazars are the most “active” of active galaxies, and near the black hole there is a lot of fast-moving gas which are moving rapidly enough that they have their own little Doppler shifts, causing spectral lines to broaden. However, some active galaxies are tilted in a way which obscures the area from which these broad lines form. These quasars are called type 2 quasars, which the teacup galaxy is.

Note: AGN means Active Galactic Nuclei and refers to the central part of an active galaxy (i.e the supermassive black hole, accretion disk and nearby regions that contribute to the spectra, and sometimes also jets). It doesn’t include the host galaxy i.e the stars. The galaxy itself is technically not an AGN but houses one, however some people use “AGN” and “Active Galaxy” interchangeably.

Its Unique Shape and Structure

Upon inspection of The Teacup, we can see 2 main features: a big central core and a tidal tail on one side, however looking into the radio shows that there are actually 2 tails tracing out 2 radio bubbles. The bubbles are likely from disturbances in the ionized gas. By taking spectra of these radio bubbles, we can see that they have a particularly high amount of Hydrogen and OIII (doubly ionized oxygen), which I’ll come back to later.

The bubbles have diameters of about 10 to 12 kilo parsecs each, which together makes the galaxy only just slightly smaller than the Milky Way. So while the AGN itself is a little small the extent of the galaxy itself is quite impressive!

We can also see the striking green tidal tail on the left, and there is actually a smaller loop on the right side too. Tidal tails in galaxies are pretty good indicators that the galaxy has merged with another one in the near past. If you want to look at a pair of galaxies merging right now, the Antennae galaxies are the perfect example to look at! The merging is likely also the culprit for the disturbed gas.

The teacup is also one a few active galaxies that are making the transition over to being a quiescent galaxy (non-active). I didn’t see this explicitly stated in any paper, but my guess is the merging reanimated the galactic nucleus and gave it another brief kick of activity and in the motion also produced both loops.

Why It’s my Favourite

It all comes down to four things:

1. It is in my favourite constellation Boötes. It technically isn’t to do with the galaxy directly, but I still count it.
2. It is an example of a galaxy merger that’s likely had a burst of activity and is now quietening down again. Merging always makes the most unique structures and is probably the cause of the green tidal tails which brings us onto point 3:
3. As a result of merging, it has two distinctly green and beautiful tidal tails of ionized gas. These tails have a significantly large amount of OIII, which is a forbidden line of wavelength 500.7 nm and is one of my favourite emission lines. Some of you may know that this is sea green and in combination with the red H-alpha it creates a lovey spring green colour. My favourite colour!
4. Finally, it is shaped like a teacup, and I absolutely love my tea!

Well there you have it, my favourite AGN! I don’t know if I have a favourite quiescent galaxy yet, because you can typically see more of the galaxy itself compared to active galaxies, there’s a lot more colour and variation that can be picked out. I’ll have to do more research!

References

Spatially-Resolved Spectra of the “Teacup” AGN: Tracing the History of a Dying Quasar by Gagne et al.

Storm in a “Teacup”: a radio-quiet quasar with ~10kpc radio-emitting bubbles and extreme gas kinematics by Harrison et al.