Galaxy evolution with MeerKAT

Overview

I’ve been working as a research astronomer at the University of Cape Town since 2018. I study various aspects of galaxy evolution, to try and understand how and why galaxies have changed over the history of the Universe.

I do this using South Africa’s amazing new MeerKAT radio telescope! It is one of the precursor telescopes to the formidable Square Kilometre Array telescope planned for the future.

Most recently, I’ve published a paper on our discovery of two giant radio galaxies with MeerKAT. It was such an interesting find that it made the worldwide news! You can read all about it on my blog post Cosmic Beasts and Where to Find Them and watch some videos on the Outreach page.

I work mainly within two main surveys being conducted with MeerKAT. They are called MIGHTEE and LADUMA. Both are galaxy evolution surveys but they have slightly different goals. More about each of them below.

MIGHTEE

MIGHTEE stands for the MeerKAT International GigaHertz Tiered Extragalactic Exploration survey. All up, it will use about 2000 hours of time on MeerKAT to peer at four different patches of sky totalling an area of 20 square degrees (which is quite a lot!).

These sky patches, or “fields” are named COSMOS, XMM-LSS, ELAIS-S1 and E-CDFS. Part of the data has already been collected, and so we have started doing some early science with it.

The giant radio galaxies I mention above were found in the COSMOS field. I’ve previously done a lot of other work with the COSMOS field. Check out Mapping the radio sky with VLA for more info.

When you do a galaxy survey, you always have to make a compromise between how much area on the sky you want to cover (wider areas give you a better chance of finding less-common galaxies), and how much sensitivity you can achieve (the better the sensitivity, the fainter the objects you can see.)

MIGHTEE is a “medium-deep” galaxy evolution survey. This means it covers a medium-sized area of sky with a medium-sized level sensitivity. But don’t let the word “medium” fool you…MIGHTEE is the best galaxy evolution survey of its kind ever conducted!

I work on two different aspects of MIGHTEE: continuum radio astronomy (similar to my work described in Mapping the radio sky with VLA) and spectral line (HI) radio astronomy (similar to my work described in Gas in galaxies with Parkes).

With this data, I am studying galaxies that are forming lots of stars (called starforming galaxies) and also galaxies which contain supermassive black holes which are wreaking general havoc (called Active Galactic Nuclei, or AGN).

At the moment, I’m particularly interested in what allows some AGN to grow to huge sizes – called giant radio galaxies (GRGs). This might help us understand the role of supermassive black hole activity in the overall evolution of galaxies throughout the history of the Universe.

I’m doing this by looking at GRGs in the MIGHTEE continuum sky maps, and comparing them to my own MeerKAT data which is at a lower frequency. In this way, we can find out more about how these huge things are aging.

With the MIGHTEE spectral line data, I’m studying the neutral hydrogen gas (HI) inside galaxies. This gas is the raw fuel for star formation. Without it, the galaxy can’t form new stars. I’m trying to figure out whether AGN have more, less, or the same amount of gas as starforming galaxies. Could this explain why AGN and star forming galaxies often look so different?

LADUMA

LADUMA means “it thunders” in the Zulu language. In this context, we use it as an acronym which stands for Looking at the Distant Universe with the MeetKAT Array. This is a “narrow-deep” survey of hydrogen gas in galaxies. It uses MeerKAT to stare at only one small patch of sky, but for many thousands of hours. This way, we expect to be able to detect HI in galaxies out in the depths of space which we have never been able to probe before at these wavelengths. What will we find? Only time will tell.

We’re still in the early stages of this project, so I can’t show you any pics yet. Quite a lot of the initial data has been taken though, and team members are hard at work processing it.

My role is to help with the “source finding.” This is just a fancy way of saying that I’m trying to find the galaxies in the data. It’s not so easy, since the data comes to us not in the form of a 2D image, but in a “cube”. It’s like a movie, where each frame is an image of the sky at a different wavelength.

The radio light from a galaxy is split over these different frame of the movie, which can sometimes make it difficult to spot. In the past, source finding has been done by eye, but with new telescopes like MeerKAT we simply have waaaay too much data to do it all by eye. So I’m trying to use a computer algorithm called SoFiA to find the galaxies. Hopefully we will find some very interesting ones really far away!

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