The Cosmic Savannah - Episode 53: Space lasers!

Jacinta00:05

Welcome to The Cosmic Savannah with Dr. Jacinta Delhaize

Dan00:08

and Dr. Daniel Cunnama. Each episode, we'll be giving you a behind-the-scenes look at world-class astronomy and astrophysics happening under African skies.

Jacinta00:16

Let us introduce you to the people involved, the technology we use, the exciting work we do, and the fascinating discoveries we make.

Dan00:25

So sit back and relax as we take you on a safari through the skies.

Jacinta00:32

Hello and welcome to episode 53. Today we will be hearing from Associate Professor Sarah Blyth and Dr. Marcin Glowacki.

Dan00:41

Hello, and yeah, today we'll be talking about a new discovery. We're talking about science and some exciting new science coming out of MeerKAT.

Jacinta00:50

We're going to be talking about a space laser.

Dan00:54

Mmm, "laser".

Jacinta00:56

Dan is doing quotation marks.

Dan00:58

You can't see the quotation marks. "Laser".

Jacinta01:03

What was it we were debating last time? I know there was like the collective noun for galaxy clusters or something like that. Oh no. And zombie stars, I think, for pulsars. You also disagreed with that fantastic term.

Dan01:18

And it's our third birthday. Three years.

Jacinta01:21

Yeah. The Cosmic Savannah has now turned three years old. We're still going strong.

Dan01:26

Good on us. It feels like just the other day.

Jacinta01:28

And good on you, listeners, for going on this journey with us and sticking with us. And for all of our new listeners, you are very welcome. And we're glad to have you on board.

Dan01:37

Yeah. And for your support. I mean, we've had a huge number of downloads now and we really appreciate that.

Jacinta01:43

Definitely. So here's to more safaris through the sky. Anyway, in my opinion today, we were talking about space lasers. Daniel, in your opinion, what are we talking about?

Dan01:56

Yeah, we're talking about stimulated emission, which is essentially a laser, but maybe not in sort of colloquial understanding of laser. So that's something we can talk about.

Jacinta02:07

Well, it is exactly the same as a laser, but just it lasers in microwave and radio wavelengths instead of optical. So...

Dan02:14

Well, that's the maser, right? That's actually a maser. It's not a laser. That's a maser. But yeah, the mechanism is the same. But I don't know, I'm just cautious of throwing that word out there...

Jacinta02:24

Misleading.

Dan02:26

Yeah, misleading.

Jacinta02:27

Alright, but technically laser stands for light amplification by the stimulated emission of radiation.

Dan02:32

Yeah, which is what it is.

Jacinta02:33

Yeah, it is all of the above. Just the light happens to be at longer wavelengths.

Dan02:38

All right. We're talking about space lasers.

Jacinta02:40

Okay. So to explain that further, what we're actually talking about today is the LADUMA survey, which is one of the big projects that MeerKAT spends most of its time observing. So it spends most of its time observing what we call LSPs, large survey projects. And we've spoken about a few of them previously on this podcast. We've spoken about the MIGHTEE galaxy evolution survey. That was, I believe, episode 31 with yours truly as the guest. We spoke about MeerTRAP with Marisa Geyer in episode 40. What else have we spoken about Dan? I think there was also MeerTime about pulsars.

Dan03:20

Yeah. So there are a lot of individual projects working on MeerKAT. We've talked about that before. Like it has different areas of expertise, where it can sort of focus and look at different scientific challenges. So we're looking at different objects, we're looking at stars, we're looking at pulsars, we're looking at galaxies, we're looking at gas. And each of those are done in different surveys, a lot of them complementary. And LADUMA is one of those surveys, which we'll be talking about today.

Jacinta03:46

This is one of the two surveys that I'm very heavily involved in - MIGHTEE and LADUMA. And they are both very good for studying the evolution of galaxies, which is of course my field of research.

And this is actually the one that I spend the most time on currently. I'm one of the two leads of the source-finding working group, which we'll explain a little bit more about later. But basically, once the data is taken from the telescope, it doesn't come out in a nice format and it has to be processed into like this 3D data cube. It's like a map of space, but in 3D. And then once you've done that, you then have to go and find the galaxies inside that data cube. And so that's called source-finding, you're finding the source of the radio emission. And so myself and Marcin Glowacki lead that working group, and Marcin is our second guest on today. And he's going to be speaking about a very, very exciting discovery. In fact, the first discovery that's been made with LADUMA, the very first scientific publication that's come out of it.

But first we'll be hearing from one of the co-leads of LADUMA, one of the principal investigators of the whole international project. And that is Associate Professor Sarah Blyth. And she's going to explain to us how LADUMA got started and what it's about. And basically it's hunting mostly for this neutral hydrogen gas, which is also called HI, which is kind of like a dully glowing gas between galaxies that helps to form stars. And it might sound like it's just this boring floating gas, but actually it's a really essential component of galaxies, which is really hard to spot. And so that's why we're doing surveys like LADUMA with MeerKAT, which have never been able to be done before, because we've never had a telescope quite as powerful as MeerKAT before.

Dan05:32

So without further ado, let's hear from Sarah.

Jacinta05:35

Was that all-encompassing?

Dan05:39

That was a lot of ado.

Jacinta05:40

That was a lot of ado. Okay. Sorry. We'll leave the rest for our guests to explain.

With us today is Associate Professor Sarah Blyth from the University of Cape Town. Welcome Sarah.

Sarah05:58

Thanks very much Jacinta and Dan. It's great to be here.

Dan06:00

Welcome to The Cosmic Savannah.

Jacinta06:02

So Sarah, you and I know each other very well. You were in fact my boss, I guess, for the last few years when I was a post-doc at UCT, and now we are colleagues, now that I have ascended the ranks to lecturer.

Dan06:16

Tell us how that was Sarah?

Jacinta06:19

No, we don't need to talk about that.

Sarah06:22

It was a pleasure, Dan. It was a pleasure.

Jacinta06:26

That's the right answer. And you and Dan know each other quite well, don't you?

Sarah06:31

For many years. I think I've known Dan since he was a PhD student, even. A long time now.

Dan06:38

Why do we have to say "long time", Sarah? This is just the other day.

Jacinta06:41

We don't need to date this.

Sarah06:44

No, none of us need to be dated.

Jacinta06:48

Okay. So we know who you well Sarah, but for our listeners, can you tell us a bit about yourself?

Sarah06:52

Sure. So I'm Associate Professor Sarah Blyth and I'm based up at the University of Cape Town. Did my PhD actually originally in physics and then moved over into astronomy for my post-doc. And I've been at UCT since 2007. I was a post-doc first. And then I started off as a lecturer. And since then, I've been a member of the faculty teaching "Introduction to Astronomy" to first-year students at UCT and doing research in extra-galactic astronomy.

Jacinta07:25

And now you are heavily involved working with the MeerKAT telescope. Is that right?

Sarah07:30

That's right. We're very excited because it's been a long time coming. We actually were involved right at the very beginning before MeerKAT was even built, thinking about what surveys we could do with the telescope. And so it's really exciting now that it's actually working so brilliantly that we can start to do science with it.

Dan07:49

And you're leading one survey in particular - you're a co-PI on the LADUMA survey right?

Sarah07:55

That's right. My two colleagues and I, Professor Andrew Baker from Rutgers in the U.S. and Professor Benne Holwerda from the University of Louisville in Kentucky in the U.S. The three of us together co-lead the LADUMA survey on the MeerKAT. LADUMA stands for Looking At the Distant Universe with the MeerKAT Array and will be one of the deepest observations of neutral hydrogen gas in galaxies ever to be done.

Jacinta08:23

Okay. So when you say deep, what does that mean?

Sarah08:25

That means that we're going to stare at one patch of sky for around three and a half thousand hours. So because of the MeerKAT's very wide bandwidth, in other words its frequency range, it will enable us to be able to measure the emission from neutral hydrogen gas back to when the universe was only one third of its current age.

Jacinta08:45

That's pretty far back.

Dan08:47

That's pretty far up. So maybe we can just unpack that a little bit more. So you know in terms of deep, right, we were looking very very far back into the universe. You said three and a half thousand hours. So is that kind of the equivalent to a three and a half thousand hour exposure of an individual patch of sky?

Sarah09:08

So it's a little bit different for optical and radio astronomy, Dan. In radio astronomy, the signals from outer space are really weak. And so we have to observe in the radio for much longer than we would ordinarily observe with an optical telescope. Star light is much more energetic and the signals are much stronger. So we are able to see far more distant galaxies in their star light much more easily than we can in the radio. So radio telescopes need to be built really big so that they can be very sensitive, so that we can pick up these very faint signals from very distant galaxies.

Dan09:43

And then you mentioned, you know, there's a wide range of bandwidths. So when you're looking back, are you looking in all of these bandwidths, all of these frequency ranges simultaneously, or are there different signatures at different distances, or you know different times in your observation routine?

Sarah10:01

Right. So you can think of the radio telescope a little bit like tuning your FM radio to pick up signals at different frequencies. And on the MeerKAT, we'll be using two of the receivers... the L-band receiver, the ultra-high frequency, or UHF receiver. And they cover slightly different frequencies. And the UHF receiver covers very low frequencies. And that's where we will see emission from neutral hydrogen gas which is very far away. So as the light travels from very far away, it gets stretched to longer and longer wavelengths and, in other words, lower and lower frequency. And so we need to be able to measure how much it's stretched out. And so the lower frequency band of MeerKAT allows us to see the light coming from neutral hydrogen gas from very far away.

Jacinta10:56

So this is redshift right?

Sarah10:58

That's correct. That's redshift.

Jacinta11:00

Okay. So the higher the redshift, the more distant the gas that we're looking at and the lower the frequency. Right. Okay. So you've talked a lot about hydrogen gas. What is that and why is it important and why do we want to study that?

Sarah11:15

So the hydrogen gas is one of the major components along with the stars and dark matter in galaxies. And the hydrogen gas is what eventually is used to form stars. It's the fuel for star formation. And so it's a very important part of a galaxy. But until recently, very little has been known about the neutral hydrogen component of galaxies beyond galaxies in the local universe. And this is because the signal that comes from neutral hydrogen gas is very weak. And our previous generation of radio telescopes could only observe the signals coming from quite nearby in the universe. Otherwise they would've had to observe for ridiculous numbers of hours, even more than thousands and thousands of hours, to see anything. And so the exciting part of what the MeerKAT brings us is it allows us to probe what the gas is like in galaxies at much greater distances than we've ever been able to do before. So it's really really exciting and leading up to the Square Kilometre Array kind of science that we hope to do once that larger part of the telescope has been built.

Jacinta12:21

And the name LADUMA, as you said, Looking At the Distant Universe with the MeerKAT Array. Okay. We've talked about MeerKAT. We've talked about the distant universe. But that's actually a really clever name. Do you want to explain more about the meaning behind that?

Sarah12:34

Yes, it's got quite a few meanings. In fact, we were putting in the proposals around the time of the Soccer World Cup 2010. And so 'laduma' was a really nice topical word at the time because 'laduma' means 'it thunders' in Zulu. And it's also what people shout when a goal is scored in soccer. It had a bit of a soccer theme. But in addition to that, the volume that we will be looking at in space as we look out in the universe... because of the changing frequencies of the MeerKAT receiver, we end up looking at a shape in space that is like the shape of a vuvuzela - one of those trumpets that people like to blow at soccer matches in South Africa... very famous instruments. And so it all fits together quite nicely. The 'laduma', the vuvuzela, you know, mapping out the space that we'll be looking at in our survey.

Jacinta13:28

If you watch the 2010 World Cup, I believe it was which was held in Cape Town and the TV... like the noise...

Dan13:36

Well South Africa in general.

Jacinta13:37

Yeah. Sorry. In South Africa. And the noise from the crowd was blaring with these like kind of horned instruments. They were the vuvuzelas, which I'm now the proud owner of one very plastic vuvuzela which I bought at the Cape Town... what do you call it, the stadium?

Sarah13:54

Yes.

Jacinta13:54

Cape Town Stadium. Yeah. Dan, can you give us a rendition of the 'laduma' cry?

Dan14:00

I think, no. My vuvuzela is at home but I think that we can... oh the 'laduma' cry.

Jacinta14:06

Yeah. Come on.

Dan14:08

I don't know if I'm prepared to do that. I think what we can do is either we can splice on both the vuvuzela and a laduma or we will just add it to the blog. We can do a YouTube link or something.

Jacinta14:21

Maybe. Yeah I don't think we need to torment our listeners with a vuvuzela.

Sarah14:27

I think it drove quite a few of the crowd mad when they couldn't really hear what was going on, but it's a very South African thing and it does show the crowd's appreciation of the soccer.

Dan14:39

I love them. And I think that the feeling I have towards them is if you don't have one in your hand, it's a very irritating instrument. If you do have one in your hand, it's amazing.

Jacinta14:50

Yes absolutely. I used my vuvuzela during the early stages of lockdown. Remember when everyone used to go into their balconies at night and, you know, cheer for the first responders, emergency health care workers. And so I would blow my vuvuzela and our downstairs neighbour would actually play the bagpipes every Friday night which was amazing. Yeah.

Sarah15:14

Very interesting combo of instruments.

Dan15:18

We had a similar thing. I used to play my vuvuzela and there was a guy across the road, he had a trumpet. So that was pretty fun too. Some good things from lockdown. Good.

Jacinta15:29

Well yeah. Anyway that's enough about instruments. Let's get back to the science and I have completely lost my train of thought. Dan, did you have the next question?

Dan15:38

Yes. I think that, you know, Sarah, you spoke a little bit about looking at the gas in very early galaxies. And I guess what LADUMA is trying to do is fill this galaxy evolution curve. So, you know, when we look out into the universe, if we look very closely, we can see galaxies how they are now. They have, you know, certain colour stars, certain ratio of gas to stars, and certain amounts of hydrogen gas. But we don't get to watch galaxies evolve over time because they evolve over billions of years. But what we can do is look back in time to the very early universe. And in that way, we're trying to piece together this puzzle of how galaxies form and evolve. And, you know, I think that that's kind of what's exciting about LADUMA, isn't it? That we we're going to really be able to look back at this gas content further than we've ever looked before.

Sarah16:30

That's right, Dan. And the exciting thing is that we'll almost be able to take snapshots at different stages of cosmic time over the history of the universe and be able to measure the gas in galaxies at these different epochs to see how it has evolved over time until the present day. And I think that will cast a lot of light on how galaxies have evolved, especially in their gas content, which we will then be able to combine with information from their star components to get a really much much fuller picture of how galaxies have evolved over time.

Dan17:07

Because it's not fully understood, right? Like, you know, how the gas content of the universe has sort of turned over from the early universe to now.

Sarah17:16

No. No, it's not understood. And we know that, you know, around redshift two or some people call that 'Cosmic High Noon', galaxies were forming stars at a huge rate. And today, when we look at how galaxies form stars, they're forming stars at a much slower rate. And so the interesting question is what has happened over the age of the universe that has slowed down the rate of star formation in galaxies. And we think that it must have something to do with how much gas that they have to form stars. It could also be to do with how many interactions they're having with other galaxies - how many mergers and collisions they're having with other galaxies. There's all sorts of different components that could be playing roles. But the gas must be one of the main components, given that it's the fuel for star formation.

Jacinta18:04

And what are some of the other goals of LADUMA? Because it is actually quite wide-ranging.

Sarah18:10

We would like to measure how the overall cosmic gas density of the universe has evolved over the age of the universe. We know how to measure that in the local universe by adding up all the gas that we find in galaxies in the local universe. But we can't until now, we've had to probe it indirectly using other methods. And so what LADUMA will help us do is measure it more directly by looking at the gas directly observed in distant galaxies. For the first time, we'd also like to measure what's called the neutral hydrogen mass function, which basically means how much gas is tied up in individual galaxies. How do their masses of hydrogen vary as we look back in different epochs or over different cosmic times. That can tell us a lot about galaxy formation models and how galaxies form and evolve over time.

Jacinta19:04

So a whole Smörgåsbord of things we can discover about galaxies with their hydrogen gas.

Dan19:09

You mentioned that LADUMA is looking at a very small patch of sky. How many galaxies are you estimating or how many galaxies have you observed in this small patch? And then how do you choose a patch?

Sarah19:22

That's a good question. There'll be many tens of thousands of galaxies in this patch of sky, Dan. Because the patch of sky stretches literally back very far out in distance from the Earth even though the area of the patch is not very large. We expect to find of the orders of 10 000 direct detections of hydrogen gas in galaxies in that field. But there are far more optical and infrared galaxies that we already have seen because we've already got a lot of other data on this field.

The field was chosen because it's actually a patch of sky that's very rich in data that's already been taken with many telescopes. We've got infrared data. We have optical data. We have a lot of optical spectroscopy which allows us to know what the redshifts of many of the galaxies are already in the field. And all this information together will help us piece together what's going on in the galaxies that we finally also measure in hydrogen emission. The patch of sky that we've chosen is called the Extended Chandra Deep Field South. And it also has essential pointing in the middle of the field which is by the Hubble Space Telescope. So we have, yeah, all sorts of really great imaging and spectroscopy on the field already.

Dan20:41

So it's a nice, like well-studied specimen.

Sarah20:44

That's right.

Dan20:45

But obviously not with radio up until now, right?

Sarah20:48

Not deep radio until now. I think there's some very shallow observations. Nothing to the level of LADUMA and nothing over the same area as LADUMA.

Jacinta20:58

Okay. So we're going to get deep-space observations of the hydrogen gas in these galaxies that have already been looked at by Hubble and all of these other telescopes?

Sarah21:07

That's right.

Jacinta21:09

So three and a half thousand or so hours of observation with MeerKAT. That's a heck of a lot. How long is this going to take?

Sarah21:16

Well probably around five years. We've been observing for just over a year so far and we have a couple hundred hours of data. But obviously we have to share the telescope with all the other surveys and people doing their own observations using the MeerKAT. And so we have to time it over the lifetime of the MeerKAT to complete the survey. It also takes quite a long time for us to reduce our data. And so it's good to have some gaps in between taking it so that we've got time to reduce it calibrate it and get it into a form that we can analyse.

Jacinta21:53

Yeah, it's a lot of complicated processing that you have to do before you can actually use the data.

Sarah21:58

That's right.

Dan21:59

And, of course, you can make discoveries in the meantime, right? You don't need the full data set and we'll be talking about one of those discoveries shortly with Marcin.

Sarah22:07

Exactly. That's the really wonderful and exciting thing that the MeerKAT is such a sensitive radio telescope that even with a single track, we've made a great discovery that I'll leave up to Marcin to discuss later with you guys. And so yes. Even small amounts of the data are very useful. They also teach us how to analyse the data because we've had to develop new calibration methods and all sorts of things to be able to deal with the vast amounts of data coming from MeerKAT. And yes, we'll be able to do a lot with even a couple hundred hours.

Jacinta22:39

And a single track, that means just one night, right?

Sarah22:42

And that's just one night. That's about seven and a half hours of data, you can already see...

Jacinta22:47

Wow.

Sarah22:48

... see signals. That's right. I'm not going to give it away.

Jacinta22:51

I can see that you're not going to give a spoiler for our next chat with Marcin. Great. So listeners, stay tuned to hear about what the big exciting discovery is. And how does it feel, lastly Sarah... how does it feel to lead a big international team of researchers to study the distant secrets of the universe with one of the most powerful radio telescopes on Earth? No big deal.

Sarah23:15

You know it's been quite an exciting and long process. We actually put in our proposal to do the survey with MeerKAT when my oldest son was born and he's about to turn 13.

Jacinta23:29

Oh my goodness.

Sarah23:32

It's, you know, it's been a really exciting journey. It's been a long time coming and it's just so exciting that we're getting to the point now where we are taking data and making really exciting discoveries. We do this as a real team effort. There are three of us as I said earlier who co-lead the survey we've each got our individual roles on it. And we have 80 collaborators as well from all over the world, including both of you LADUMA members. And, you know, so it's really a team effort. And I think the strength is that we've got people who are experts in all sorts of different areas coming together to give their expertise where it's needed.

Jacinta24:11

I just realized that the idea for LADUMA was born the year that I started my PhD.

Sarah24:16

Yeah, it's quite a timely thing. It's been a long time in the planning and the preparation and it's amazing that it's finally coming to fruition and that the first paper's been accepted. Yeah. We're very excited and we hope that it's just exciting times ahead. We've got lots of science projects on the go now with our first data release coming.

Jacinta24:36

My first ever trip to South Africa, I attended the LADUMA. One of... I think the first LADUMA meeting. And we went it was part of the public engagement aspect of the survey, we went to all of these different schools in Cape Town. We partnered up and we went to give these amazing talks in schools. And that was so much fun. It's like one of the most memorable experiences of my life still to this day.

Sarah24:58

Well that's wonderful. I actually remember a photo of you, Jacinta, and I think you were running up and down the hall yelling 'laduma'.

Jacinta25:05

Yes.

Dan25:08

We need to repeat that.

Sarah25:20

Just wishing we had a recording of that.

Dan25:20

Does that still exist?

Sarah25:20

We might somewhere.

Jacinta25:20

I've never seen that.

Sarah25:21

I remember that very clearly. The lovely photos that came back from that.

Dan25:22

Sarah, I will pay you a lot of money if you can find that.

Jacinta25:27

Oh dear. Oh dear. Okay. All right, I think that's it Sarah. Thanks for telling my secrets. No, but thank you very much Sarah for joining us. Congratulations on getting the survey to where it is now. And we look forward to a lot of amazing discoveries coming out of it in the very near future.

Sarah25:44

I'm very excited too and thanks very much for having me. And hopefully we'll be back soon with some more to tell you guys.

Dan25:51

Thanks I look forward to that. And just before you go can you just let the audience know, you know, where they can find out more about LADUMA, or follow yourself on social media, if you do social media.

Sarah26:01

So we have a webpage, a public webpage, which is www.laduma.uct.ac.za. Or you can find us on Facebook under LADUMA. And we have a Twitter handle, LADUMA_MeerKAT. If you'd like to follow us on Twitter, that's probably a good one to follow for the latest updates on anything exciting coming out of the survey.

Jacinta26:24

Great. And that's MeerKAT spelt M-E-E-R-K-A-T. I actually can't remember Is that how you spell normal meerkats?

Sarah26:31

It is.

Jacinta26:31

It is. Okay. There we go. Oh, okay. Great. Yes. So once again, thank you very much Sarah for joining us.

Sarah26:42

Thanks a lot.

Jacinta26:43

It's been great.

Sarah26:45

Been great too.

Dan26:50

Thanks Sarah. We had a great chat with Sarah I think that was awesome to hear the background for LADUMA... how it all came about. And, you know, now that it's running, it's been a long time coming and we're getting our first paper out which is what we're going to be chatting to Marcin about in a moment. And we talk about these things in almost every episode, it feels like... how exciting MeerKAT is and all the exciting things we are hoping to get out of it. And yeah, here comes another one.

Jacinta27:18

Yeah. But it's just true but yeah. So Sarah spoke a lot about the hydrogen gas that we're searching for in these galaxies with LADUMA, but there's actually something else you can look at with the same dataset. And that is masers, as we were talking about at the start of the episode, AKA space lasers.

Dan27:41

All right. So here it is. We get to talk about space lasers.

Jacinta27:45

We get to talk about space lasers. Now basically, they are hydroxyl molecules which are one atom of oxygen and one atom of hydrogen joined together in a molecule that you can call either hydroxyl or OH. And this is kind of in it's formed inside dense clouds of gas so much more dense than the hydrogen gas clouds we were talking about previously, and often this gas becomes due to the collision of two galaxies. And when that happens, it can stimulate the emission of the radio light from these hydroxyl molecules. So you basically get this blaring space laser in the radio from within these very distant galaxies. That happens to be emitted at a particular frequency of light that you can actually see in this data that we got from LADUMA. But it's actually really quite difficult to find these and very rare. And so spoiler alert, one has been found in LADUMA data. We're going to hear from Dr. Marcin Glowacki now who actually made that discovery and has written the very first paper from LADUMA.

Dan28:53

And we should point out that... so this is not what LADUMA was designed to detect right?

Jacinta28:58

No, no, not at all. Well I mean partly but mostly it was designed for detecting HI and then kind of some people came in and said, "Oh well do you know that there's actually OH can be found at these wavelengths. Maybe we can look for that." And so yeah, that became a part of it, but it was actually designed for HI as far as I know.

Dan29:19

Awesome. So we're getting additional science out of it.

Jacinta29:22

Absolutely.

Dan29:24

All right. Let's hear from Marcin.

Jacinta29:33

With us today we have Dr. Marcin Glowacki who is a researcher at the Curtin University node of the International Centre for Radio Astronomy Research. Welcome Marcin.

Marcin29:44

Thank you very much for having me Jacinta.

Jacinta29:46

Marcin, now you and I know each other well, but for our listeners, can you tell us who you are where you're from and what you do.

Marcin29:51

Certainly. I'm Marcin Glowacki I'm a post-doc currently working in Perth on fast radio bursts. I grew up in Australia and I did my PhD at the university of Sydney. Then I moved to Cape Town to work for IDIA and university of the Western Cape. There, I was working on two main areas of research. One was HI emission surveys or neutral hydrogen surveys with MeerKAT and also the Simba hydrodynamical galaxy simulations.

Jacinta30:20

All right. And so you and I didn't know each other before but we're both Australians who then moved to South Africa to work with the MeerKAT telescope. We actually were office mates. And now we are both back in Australia, in Western Australia, in Perth, although myself supposedly temporarily.

Marcin30:37

Small world indeed.

Jacinta30:38

Okay. So you've been working on studies of hydrogen gas in galaxies and also simulations. Tell us a little bit about these simulations. You said it was called Simba?

Marcin30:47

Simba. Not named after the band of potato chips, but rather named as fun after the character from the Lion King.

Jacinta30:56

Okay. Yes. So that's a South African brand of potato chips right? Which we now know.

Marcin31:00

Yes. This is a vague useful set of galaxy evolution simulations that allow you to make direct comparisons to observations with upcoming surveys such as those on MeerKAT. So part of my work was making predictions for what we can expect to see with the MeerKAT telescope.

Jacinta31:19

Right. So you were predicting what we expect to see, but then you are also working with the LADUMA survey right? And actually seeing things. Tell us about what LADUMA is and your involvement in that.

Marcin31:29

Yeah. So the comparison I made was directly to LADUMA. It stands for Looking At the Distant Universe with the MeerKAT Array. And this is one of the main science survey projects for the MeerKAT telescope based in South Africa. And it will be looking for the neutral hydrogen or HI gas in galaxies. It will also be the deepest such survey and this is achieved, one by using a fantastic telescope such as MeerKAT with great sensitivity, and two by using it for a really long time. So we're spending over 3000 hours looking at one patch of the sky. So we can go further than we ever have with this kind of survey.

Jacinta32:08

Okay. So now Marcin and I actually work very closely together because we are the co-leads of what's called the LADUMA source-finding working group. So Marcin, can you explain to our listeners what source-finding is and why do we need to do it?

Marcin32:25

Source-finding is literally looking for the source. So we need to identify the galaxies that we detect in neutral hydrogen. And it's very important to be careful that we find everything that is there to be seen and we don't have any false positives. So there's a few ways you can do that. One way is just visual source-finding using a human to look at the 3D data cube that comes out of MeerKAT.

Jacinta32:48

Which is what you do?

Marcin32:49

Yes. That's what I've been leading. And we can also look at automated or algorithms to help detect. So it's not so much of a strain on people who can still make mistakes. So we're using the two together to come to the best solution to get the best results.

Jacinta33:06

So I'm leading the automated source-finding one and I guarantee that the automated source finder definitely still makes mistakes. So we're trying to find the best solution of all of the above.

Marcin33:17

Yes.

Jacinta33:19

Okay. So once you get the data from the telescope, and we've got this particular dataset from LADUMA, we then process it and make kind of like a 3D cube, like a map of the sky in 3D. And then we have to go and find the galaxies in all the sources of emission, the sources of light, of radio light. Now you started doing this a while back, Marcin, and you found a really interesting object, right?

Marcin33:43

Yes. Indeed. So I'll take you back to the wonderful times known as 2020.

Jacinta33:49

Don't we want to forget those times?

Marcin33:53

The joys of lockdown. This was a period of time as I'm sure many people in South Africa and around the world are familiar with, but lockdown was quite strict in South Africa. We, for a while, couldn't even go out for exercise, but luckily I had a decent enough up setup. And part of my work was looking at these 3D cubes that came out a MeerKAT. We were trying to work on how we should best reduce the data for this very deep, very long survey, so we can combine all the observations and gets the best results. And part of that involves looking at the cubes for data verification. So one afternoon, when I was working from my desk or dining table in my apartment, I was taking a look at some of these cubes at the lower radio frequency ends. Basically, it corresponds to galaxies that will be further away from us.

Jacinta34:40

That's because of the redshift of the universe, right? How it stretches light the further away the light is coming from.

Marcin34:46

Yes, exactly. And I wasn't at the time expecting to find a detection. I was more focussed on looking at the quality of the noise - if there's any artefacts in the data, something annoying called radio frequency interference, for example, that might wipe out some frequency space.

Jacinta35:01

From like satellites and stuff that are getting in the way?

Marcin35:03

Satellites, radio towers so on and so forth. But as I was looking through the cube, I noticed one source suddenly pop up and fade away as I moved through frequency.

Jacinta35:13

What did it look like? Kind of like a bright blip or something?

Marcin35:17

Yeah. Like a blob small blob of light coming in and out. And luckily around then, I also had a second observation to do some data verification on. And I looked at it and the same source was popping up at the same frequency and the same position in the sky. So it looked quite convincing.

Jacinta35:33

Okay. So you saw it in the same position in two different datasets taken at different times?

Marcin35:39

Yeah. Taken on different nights slightly different number of antennas between the two observations. So the fact that you see it twice makes it very convincing.

Jacinta35:47

So you think it's definitely a real source?

Marcin35:50

Oh, I was sure of it once I saw it twice.

Jacinta35:52

Okay.

Marcin35:52

So I thought to myself well this might be HI in emission quite a distant galaxy, not breaking any records, but still maybe there's something quite interesting because since it's so far, it must have a lot of gas to be able to see it already in one night of observation. Since I had the position, I could look into the literature and see what other observations of that patch of the sky existed at different wavelengths, because different wavelengths give us different information about space. And I found that there was a galaxy detected in other wavebands including optical and it had a measured redshift. The thing was if it was HI, we would expect the redshift of 0.31 and this was a redshift of 0.52. So much further away.

Jacinta36:40

So this is distances? So if it was hydrogen gas, we expect it to be at a certain distance from us. And if it was... but you're saying that the signal wasn't it was from much, much further away?

Marcin36:51

Correct.

Jacinta36:51

Okay.

Marcin36:52

And it turns out that this redshift or 0.52 corresponds not with HI or neutral hydrogen but with hydroxyl molecules, OH, one atom of oxygen and one atom of hydrogen.

Jacinta37:05

Okay, so it's an atom of oxygen and atom of hydrogen joined together to form something called OH or hydroxyl, right? Okay.

Marcin37:13

Correct.

Jacinta37:14

So you did various tests and you decided, okay, this is definitely not the signature of hydrogen gas? This is the signature of hydroxyl or OH.

Marcin37:23

Correct.

Jacinta37:23

Okay. So what's important about that? What's important about a hydroxyl?

Marcin37:27

So this sort of emission in hydroxyl is known as 'masing'. So basically like a laser but in a different part of the electromagnetic regime, so microwave, radio and infrared.

Jacinta37:40

Okay. So not a laser but a maser.

Marcin37:43

A maser, correct.

Jacinta37:44

So this is a space laser basically but with an 'm'?

Marcin37:48

Yes

Jacinta37:49

Cool

Marcin37:49

Yes. And And not just a space maser because in this case we're looking at a galaxy which had just undergone a recent merger. So two galaxies have collided and formed a bigger galaxy. And this will make a lot of dense gas within the host galaxy. And this amount of gas hydroxyl molecules is so bright that we could see it over radio telescopes such as MeerKAT. So this is a space laser on the size of galaxies.

Jacinta38:18

So this is an epic space laser?

Marcin38:21

Yes. In other words, the term is 'mega-maser'.

Jacinta38:25

Oh mega-maser. There you go. A hydroxyl mega-maser. Wow. Okay. So how was this mega-maser formed?

Marcin38:34

So as said, as two galaxies merge, you have a creation of a large amount of gas and these molecules will start interacting with each other. We'll take a simple case of one hydroxyl molecule when it absorbs light or photons with energy equivalent to the wavelength of 18 centimetres which is what we can see with a radio telescope. It will emit two photons. So