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:

Related links

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.

Mini Episode: Beyond the zone of avoidance

with Sambatriniaina Rajohnson

Hosted by Tim Roelf

This week’s mini episode features PhD candidate Sambatriniaina Rajohnson, of the University of Cape Town’s Astronomy department. She explains part of her work trying to advance our understanding of the large scale structure of the universe.

Using the radio telescope MeerKAT, she plans on observing these structures in a region known as the Vela supercluster. This all part of her contribution to the Galactic Plane Survey (GPS).

She describes some of the challenges she faces in studying the region of space hidden by the Milky Way – the formidable Zone of Avoidance.

A 3-D render of the 2MASS Galaxy Redshift Catalogue (XSCz) which highlights the zone of avoidance. This is what our local universe would look like if we could view it from the “outside”, with each dot representing an entire galaxy, and the colours giving us a measure of distance. The zone is created from the Milky Way blocking our field of view. Image credit: T. Jarret

This week’s featured guest

Featured Image

2MASS Galaxy Redshift Catalogue (XSCz): The local universe as seen in the near-infrared spectrum, and displayed in an equal-area projection, with the Milky Way at the centre. The colour of the galaxies pictured (of which there are at least 1 million!) gives us an indication of the distance between us and them. Those that are the furthest away are coloured red, while those that are closer are purple. The galactic plane is that thin line of white/tan coloured stars, and space dust, spreading out from the actual centre of the Milky Way – which happens to be a supermassive black hole! It’s the dust, stars, and black hole that obscure our vision; creating the Zone of Avoidance.
Credit: T. Jarret

Related links

If you liked the XSCz images and want to find out more about them:

Sambatra also recently got featured in a Royal Astronomical Society poster contest. The link below takes you to page with a brief summary of the poster, and a download link so you can check out her poster for yourself:

Mini episode produced and hosted by
Timothy Roelf (University of Cape Town)


Transcribed by Tim Roelf

Tim: [00:00:00] Hey everybody. And welcome to this week’s mini episode of the Cosmic Savannah. My name is Tim Roelf, and I’ll be your host for today. As some of you already know Jacinta, and Dan, have gotten in several of us trainees to perform our own little mini episodes for you guys to help us to develop our skills as podcast hosts, editors, and transcribers.

The process has been really awesome, and I hope you guys have been enjoying our work so far. This week, I interviewed Sambatra Rajohnson. She’s a PhD candidate at the University of Cape Town’s Astronomy department. And her work involves in completing a Galactic Plane Survey (GPS), some of the cool bits about Sambatra’s research involes the fact that she will be looking at a region of space known as the Vela supercluster that lies just beyond the zone of avoidance.

So if you guys just scroll around the Cosmic Savannah blog site here, you’ll be able to see one of the images has a picture of what the Zone of Avoidance looks like along with a little bit of a description. Essentially, it’s just the obscuration of dust and other stars that creates this regional space that we can’t actually penetrate.

If you guys are a little bit confused about what I mean by, or what Sambatra means, by the galactic plane, the featured image on this week’s episode is a all-sky survey that was done in the infrared spectrum and shows our local universe. Right at the center of the image you’ll see a thin white band with like tan and white colored stars and dust.

That is the galactic plane. So essentially it’s just this flat line where most of the stellar matter lies, and at the center of which is a supermassive black hole. And that creates this obscuration. And just some last technical terms before we can answer the interview, Sambatra mentions the words: uniformity and isotropy.

Now uniformity, sometimes known also as homogeneity, just means that the universe on a large enough scale has the same spread of matter, or stars, stuff really, to put it simply if you just take two large enough areas of the universe and you compare the two of them, they will have the same spread of matter across them.

And isotropy means, that the universe is the same in every direction. So it doesn’t matter if you look forward or backwards, the universe will be the same. Now enough of me talking. Let’s get down to this week’s episode.

[00:03:16] [Intro music plays]

Tim: [00:03:22] What’s up everybody, and today I’m joined by Sambatra Rajohnson. She is a PhD candidate at UCT. Welcome to the show, Sambatra.

Sambatra: [00:03:34] Hi Tim, thank you for welcoming me.

Tim: [00:03:38] Yeah, that’s no problem. I have a few intro questions quickly. So for people who don’t know you, you’re not actually from South Africa. So if you can tell us a little bit about where you’re from, and how you managed to get to UCT.

Sambatra: [00:03:51] Okay. It’s a bit of a long story, but I will try to summarize it. So I am from Madagascar and I did my undergraduate studies and I obtained my master degree from the University of Antananarivo in the capital. And during the same period, I was also participating to the DARA are basic program DARA for Development in Africa with Radio Astronomy.

And it was basically a technical training in radio astronomy observation. And from that one of our lecturer, Professor Claude Carranan, he proposed to me to do a PhD with him at the University of Cape town and I’ve accepted. So that’s why I ended up here in Cape Town.

Tim: [00:04:33] Cool, that’s very cool. And how are you finding it in Cape Town so far? Is it cool?

Sambatra: [00:04:37] Oh, it’s a very beautiful city. It’s also my first time, like really living abroad. So I’m trying to adjust myself with all the changes, but now I see it’s a very good place.

Tim: [00:04:49] Okay. That’s awesome, and so you mentioned that your project is in radio astronomy. Could you tell us a little about that?

Sambatra: [00:04:57] Okay. So I’m working with Professor Renee Kraan-Korteweg now, and Dr. Bradley Frank on the Galactic Plane Survey or GPS. And we are using the radio telescope MeerKAT, which is here in South Africa. And we are trying to find structures of galaxies that are located behind the Milky Way plane by searching for the neutral hydrogen, or H1 emission, which only radio telescope can trace.

Tim: [00:05:28] Okay. So they’re obscured by the galactic plane. How you actually able to tell. That’s something behind the galactic plane.

Sambatra: [00:05:41] Yes. So the zone, which is behind that Milky Way plane that we are trying to look at is called the Zone of Avoidance.

Tim: [00:05:42] That’s a scary name.

Sambatra: [00:05:45] Yes, a little bit. Most of astronomers are trying to avoid it, due to the strong dust obscuration, and strong steller density which hides mostly everything behind it, especially if you’re looking at optical wavelength. But, if we use other telescopes or other wavelengths, such as infrared or radio, so this obscuration is reduced. So we are not really affected so we can see things behind the Milky Way using, for example, radio telescopes.

Tim: [00:06:15] Okay. That’s very cool. Very, very cool.And your work. In that zone of avoidance, what are you looking for? Are you looking for new galaxies?

Sambatra: [00:06:26] So we are trying to to complete the mapping of the large scale structure of the sky. So we are tying to find structures that are hidden behind the Milky Way. So we have, for example, a particular region of interest, which is the Vela supercluster, which is located situated towards the constellation of Vela.

So the GPS survey will allow us to find hidden structures. How filaments are connected.

Tim: [00:06:56] Sorry, just to interrupt you. JPS, what does that stand for?

Sambatra: [00:07:01] Oh, the galactic plane survey.

Tim: [00:07:05] Oh yeah, the GPS you said.

Sambatra: [00:07:06] Yes. So we are trying to find if the hidden structures, how filaments are connected there behind the Milky way. Are there, for example, crossing walls from that Vela supercluster?

Tim: [00:07:20] Yeah. Okay. That’s cool. But I’m not very familiar with the filaments. Could you give us a little bit of an explanation on that please?

Sambatra: [00:07:27] Yes. So from the cosmological principle, it states that the universe is uniform and isotropic. However, when we are looking into details, so we are like zooming into the universe. We can see that actually the universe is highly structured. So for examples, galaxies are connected each other to form elongated filaments, or walls. And there are also small, a large concentration of galaxies, which form clusters of galaxy groups and superclusters. And between them, they are also just large empty voids. Yeah. So are forming what you are calling the cosmic web. So like web like structure in your universe. Yeah.

Tim: [00:08:09] So that’s the large scale structure. So everything is connected in what approximates a web essentially, but not like a 2-D web it’s in 3-D.

Sambatra: [00:08:23] Yes

Tim: [00:08:24] Which is really, really cool. That’s fascinating. That’s awesome. I was wondering your work, you said that by working in the radio, you’re actually able to penetrate past the galactic plane and into the zone of avoidance, which you wouldn’t be able to do in optical.

How does your work then work with the optical astronomers? So how are you guys able to back each other up essentially and provide more information into your work? For instance, if an optical astronomer would also like to, then would they be, would it be possible to look into the zone of avoidance and help you add or…

Sambatra: [00:09:06] So for optical astronomers, they cannot really look entirely at the zone of avoidance. Maybe, there will be some part where they will be able to look into, but very small part of it. And they have already tried to like make the mapping of the entire sky, but then they miss out the zone of avoidance. So maybe they have obtain some images of galaxies that are next to the sort of avoidance, but not exactly in the middle of the packed zone. There have been also infrared astronomers who try to look into it. So they have found more galaxies, so the galaxies in the zone of avoidance have been extended, but it’s not yet fully locked mapped. So that’s why you have to add with radio bands so that you can find more.

Tim: [00:09:51] Okay, that’s very, very cool. One final question, I’m just interested, So why would you use, you know, just getting into astronomy, what would you say to them, to interest them, in coming say to a presentation on your work. I suppose.

Sambatra: [00:10:06] Oh, I think my work is like quite a challenge because most of the astronomers are trying to avoid that zone. But we are looking directly into it. So it’s a challenge to be able to discover a galaxies that are being never observed in optical before, or even never found before. So yeah,

Tim: [00:10:25] So you’re kind of a pioneer. That’s awesome.

Sambatra: [00:10:32] Yes it’s challenging.

Tim: [00:10:35] Do you get to name any galaxies or stars that you find in the zone of avoidance?

Sambatra: [00:10:42] From now on, I’m just starting my project. So I don’t know yet about that. Like how are we going to name them? Maybe according to the telescope because you will be using MeerKAT. So maybe the name of the stars will be linked to the MeerKAT telescope, but I’ve not yet thought about it.

Tim: [00:11:00] Oh, I think you missed my question. Its like, would you name it, you as Sambatra, would you be able to name it because you found it, would you be able to name anything?

Sambatra: [00:11:11] From now I don’t know yet whether I’ll be able to, or not.

Tim: [00:11:14] Ok, we can look forward to a few galaxies or stars being named after Sambatra. That would be very cool.

Sambatra: [00:11:19] I hope to.

Tim: [00:11:22] Thank you very much for your time today. I’ve thoroughly enjoyed this conversation and I hope to see you again. Next time.

Sambatra: [00:11:29] Okay. See you.

[00:11:30] [Outro music plays]

Tim: [00:11:37] And that’s it for this week’s episode. If you guys had fun and want to know more about this topic, I’ve left the link in the description of the blog post above to a series of posters that Sambatra submitted for the Royal astronomical society. I highly recommend you guys go check it out. They’re really informative posts and they’ve got some really, really cool graphics as well that I think everybody can appreciate and until next time, cheers.

Episode 3: SETI with MeerKAT

with Dr Griffin Foster

In this episode Dr Griffin Foster describes the planned hunt for extraterrestrial intelligence with South Africa’s MeerKAT telescope!

Griffin is from the University of Oxford and is the project scientist for Breakthrough Listen – a program to hunt for signs of extraterrestrial intelligence using radio telescopes.

Griffin explains, in a surprisingly down-to-earth and practical way, why we might expect intelligent extraterrestrial lifeforms to exist elsewhere in the Universe, how they might be trying to communicate and how we might search for these signals.

Griffin and the Breakthrough Listen team plan to conduct part of their search with the new MeerKAT radio telescope. MeerKAT is one of the world’s most advanced radio telescopes and is located in the Karoo in South Africa.

Episode Links:

BL@MeerKAT announcement:

Berkeley SETI Research Center:

This week’s guest: