Mini Episode: Capturing the whispers of hydrogen

With Andrew Firth

Hosted by: Tshiamiso Makwela

In this mini episode, we chat to Andrew “Andy” Firth, a Masters students at the South African Astronomical Observatory and the University of Cape Town.

Andrew tries to detect the faint signals of hydrogen gas in distant galaxies using a new technique. He does this through stacking data cubes of these galaxies. This clever new technique will be applied to some of the MeerKAT radio telescope data.

Growing up in the Karoo, Andrew had the pleasure of experiencing the beautiful Southern night sky. With this experience, Andy not only fell in love with the stars from afar, but also believes that astronomy is one of the avenues of understanding the universe and our origins at large.

This week’s guest

Featured image

This image shows one of the most detailed images ever produced of hydrogen gas in a spiral galaxy (other than our own Milky Way). This galaxy is called M33. The colour shows the Doppler redshift and blueshift (direction of movement) of the gas.
Image credit: https://public.nrao.edu/gallery/

Related links
Link: https://www.cv.nrao.edu/course/astr534/HILine.html
Link: https://www.nrao.edu/pr/2001/m33gas/index-p.shtml

This episode is hosted and produced by Tshiamiso Makwela

Episode Transcript

Tshiamiso: [00:00:00] Hello, and welcome to another mini episode of the Cosmic Savannah. My name is Tshiamiso Makwela your guest host for today’s mini episode. I’m currently a PhD candidate in the department of astronomy at the University of Cape Town. My work looks at the astronomy education research field, where I aim to probe student engagement with different aspects of astronomy.

But today it isn’t about me. My guest today is Andrew Firth, Andrew is a master student at the university of Cape town and the South African astronomy observatory. He is currently working on his research on the improvement of radio data, which will be applied on some of the surveys of the MeerKAT Telescope you heard, right? The MeerKAT Telescope.

In this interview, Andrew will be sharing how he developed an interest in astronomy and the role that he’s father played in this. His research, is in HI astronomy, which is the 21 centimeter spectral line, which is created by changing energy states of neutral atoms. He is specifically looking at improving SNR through cube sticking.

So you might ask what is SNR? So SNR refers to signal to noise ratio. So he is doing cube stacking, which involves the alignment of data cubes from galaxies to flatten the noise and improve the signal. Before I give a lot away, let’s get in the interview and listen to what Andrew had to tell us.

Intro Music: [00:01:42]

Tshiamiso: [00:01:45] Welcome to the Cosmic Savannah today our guest is Andrew Firth, who is a master student at UCT, is it UCT?

Andy: [00:01:49] That that is correct. I’m based at the SAAO and thank you for having me in.

Tshiamiso: [00:01:54] Yeah, thank you for having us. So Andrew will be chatting to us about what he’s studying his masters, but also he’ll be telling us a little bit about his background and how he got into astronomy. Who is Andy?

Andy: [00:02:07] Oh, okay. As you said, my birth name is Andrew Firth a lot of people call me Andy, and I’m okay with that. If I owe something and then in that case, it’s Dennis, that’s always good to have some backup. Well, I was born in the Northern Cape, so that had a big influence on my desire to study astronomy. The night skies there are brilliance if you go to Carnarvon, which is where I’m from. Yeah, absolutely. It’s like fire in the sky. It’s just absolutely amazing.

And also my upbringing, my dad also used to show me many displays on how daylight works and how the phases of the moon work using cricket balls and a candlelight. Since that’s really only ever been one thing that I wanted to do and that was astronomy

Tshiamiso: [00:02:59] You are here doing your research in astronomy please tell us a little bit more about that.

Andy: [00:03:04] Okay. I’m essentially continuing my honors project from last year And it’s in the improvement of, so I can tell you this, the title might be a bit of a word salad.

The title generally went “Improving spectral SNR through cube stacking” and so at no point there, does it sound like I’ve mentioned astronomy?

Tshiamiso: [00:03:34] Yeah, it doesn’t [laughter].

Andy: [00:03:37] But really. This is really tackling what’s a very, very big problem when it comes to HI astronomy or the study of the 21 centimeter line. And so that’s a bunch of astronomy in radio astrophysics in my case where we studied the emission of 21 centimeter long wavelengths through a particular transition in a hydrogen atom.

And so that transition being an electron moving through various states releases a photon and that photon which is this particle of light, moves through the wavelength of that radiation as a length of 21 centimeters. And this is very useful applications in astronomy in that it’s a very long wavelength, so it doesn’t interact much with gases in between. So it travels for very long distances, but there’s a drawback. Everything has some sort of catch.

And in this case, it’s a very weak form of emission. And so the only reason we really see it is because hydrogen is so abundant in the universe. And so even though hydrogen is the most are abundant, the signal, which is the S part of this word called SNR is very weak. So what you want is a very high signal and low noise.

In other words, a high signal-to-noise ratio. And you can do this through many means. And a very popular way of doing it is through stacking data of an object or images of an object. So you take, so in conventional photography, you take multiple images, you’ll stack them, meaning you align them. And then add all the various pixels together and that usually flattens the noise and improves the signal. And of course, you have to do some averaging otherwise you’re not looking at what you think you’re looking at anymore. So you’re looking at something else.

So our task was to take this idea and to move it into three dimensions. So a sort of three dimensional picture of the galaxy. But it’s not the physical aspect of the galaxy, but more the motional aspect of the galaxy. This is very difficult to explain without moving my hands. I’ll try my best to convey it in sound. So I’m not sure if you’ve heard of the Doppler effect.

Tshiamiso: [00:06:18] Yeah, I have.

Andy: [00:06:21] So that works for sound very well. If you’ve heard the whole notion of a train coming towards you and leaving you with the whole, with the hooter. That high pitch when it’s coming towards you in the low pitch when it’s getting away from you. So in the same way, we look at galaxies using a radio telescope and there’s H one gas,that’s the hydrogen gas that’s in and around this, the sort of bowl of galaxy, this bowl of space. And this bowl is filled with, with hydrogen gas and this hydrogen gas isn’t stationary.

So it’s all moving around the center of this galaxy. So it’s rotating just like if you imagine the spiral galaxy, they tend to have a lot of it. That’s all the rotating about the center. And so if you’re looking at a galaxy, let’s take the easiest. If you just picture a spinning CD disc and you’re looking at the edge of that CD disc, one side of that CD disc, that you’re looking at will be coming towards you and the other part will be getting away from you. And so that compresses or stretches the signal the 21 centimeter line that’s coming from this hydrogen. And that gives you some sort of idea of how this galaxy is moving.

It gives you the clumps of gas that’s coming towards you and the clumps of gas getting away from you. And so in my project, we want to improve this by making sure that we align galaxies. And this is further complicated by the fact that galaxies are not all positioned the same in space. It’s all random, scattered all around. And so just like I spoke about, you have to average them. You have to make sure that the image that you’re taking is identical when you add them. Or rather the galaxies inside have the same orientation inside that data cube.

And so my algorithm, rather our algorithm that we’re trying to develop is in sort of phase two of production. Now, we are trying to make it a little bit smarter and that involves using optical properties for when you try and align galaxies inside the data cube. Hopefully, I haven’t spoken to myself into a web.

Tshiamiso: [00:08:52] This is all really interesting. You also mentioned a radio telescope I’m sure all of us have heard about radio all over, but please tell us a bit more about the radio telescope. And is that where you get your data?

Andy: [00:09:05] Yes. So radio telescope is pretty much similar to an optical telescope in that an optical telescope, collects light or photons, or focuses lights to a detector. And uses the wavelengths that we can see, which is in the nanometers range.

I can’t remember exactly, but it’s about like 500 nanometers around there. That’s the length of the wavelength. So there’s a peak and the crest, the distance between those two things is about five and over on the order of nanometers, in the case of radio. Radio electromagnetic lights or radio light, those wavelengths are a lot longer. And a lot of the particles, a lot of the photons bypass and just cannot be detected by an optical telescope. So you have to design a different telescope, which is able to collect photons from a radio source, like HI, the other sources as well, but I wouldn’t dare claim to know much about it.

But in the case of HI, which is 21 centimeter line they work on the same principle, you’re just collecting photos from a source that’s emitting radio, radio waves, radio light. So we use the data from a radio telescope array. And so to get to make data cubes, you need sort of, you need to know the delay between signals from the different parts of the galaxy. In that delay, because, because the galaxy is moving, there’s a delay between when if you again, think about the CD, analogy.

The part of the CD, that’s closest to, you gets released a little bit sooner than the part that’s moving away from you. And so there’s a sort of delay and also lengthening of the wave. And there’s also a delay the spacing between different telescopes in the array for now we’re back on earth now. And we’re thinking about how we’ve placed the telescopes that spacing allows us to infer what’s called phase shift information.

And from that a whole bunch of complicated maths, which I haven’t dealt with myself, but I trust the mathematicians and engineers, allows us to construct a data cube and -my work starts from the, the computer side of things. So I hardly, I haven’t touched the radio in my life to this point. Yeah.

Tshiamiso: [00:11:54] okay. Alright. Okay. So this has been really fascinating to know about and to know of, but why do you do this? What really motivates you to do the work that you do?

Andy: [00:12:06] A question that keeps me interested is how did we all get here? And so one way you can study that is through astronomy and you can look in radio waves, which travel much further than optical waves because of the things about extinction.

And you can look and sure as you might’ve heard before. If you look far, you look back in time as well. So if you look further away from earth, you look further back into the past and you can study the things that are far back in the past, to gain some sort of sense on the evolution of the universe, how galaxies form, how old the things that we see around us in the night sky, how they came about. Because you can see further and further. And I think, and that’s one of the main reasons why I’ve gone into radio, Extra-galactic astronomy.

Tshiamiso: [00:12:59] Oh, okay. So that’s really interesting. I am already motivated myself. [Laughter]

Andy: [00:13:07] Mission accomplished.

Tshiamiso: [00:13:09] Thank you, Andy, for being with us today.

Andy: [00:13:11] Thank you for having me.

Outro Music: [00:13:13]

Tshiamiso: [00:13:23] What an informative discussion we’ve just had with Andrew. His work in radio astronomy sounds very exciting, but yet challenging, especially trying to align the galaxies found and the HI 21 centimeter line as galaxies come in different shapes and sizes. I think Andrew gave us amazing analogies and examples to help us visualize what he is doing.

Astronomy is indeed challenging, but like I said, very fascinating as it gives us another avenue of understanding the universe better. I hope you enjoyed this mini episode with me Tshiamiso Makwela and Andrew Firth, I thank you.