I sort of. Good afternoon, everybody.
Can you hear me? Yes, I think you can. Good. Thank you.
Welcome to the physics department and welcome to this 18th INSEE lecture, which will be given by Professor Jacqueline van Goal.com,
who's been visiting as the relevant professor of astronomy at Columbia University in New York.
So Professor Van Goal.com is a radio astronomer. She studies the distribution of neutral hydrogen gas around galaxies, and in particular,
she's focussed her attention on the motions of that gas and what it can tell us about how galaxies are assembled and how they evolve.
She did her Ph.D. in the capturing lab of the Rice University in Groningen in the Netherlands, and she went from that position,
which is, I should say, one of the institutions in the world that sets the heart of this kind of world of work.
So she was trained in a really intense environment that understands how to do this kind of work.
And she went from there to the National Radio Astronomy Observatory in the United States, where this was in the early 1980s,
where she went to work at something called the very large, very large array VLA in its early days.
And she was one of the pioneers that made it possible to use that enormously powerful instrument to do this kind of work.
It's not a trivial thing at all.
It requires special techniques to be developed over and above those that were already in use at that facility in New Mexico at Socorro.
That's where I met her in the early 1980s, when I too lived in the United States.
She has been a faculty member at Columbia since 1988 and is widely recognised for her contributions.
She's been a visiting professor at Berkeley University of California, Berkeley da Vinci professor at the China Institute in Groningen.
She's a corresponding member of the Royal Dutch Academy, and she has two attributes in common with somebody else who's here.
I can't quite see how I can see her now. In Belbin, who's a visiting professor in our department.
She was a member of the Site Selection Advisory Panel for the square kilometre array.
That is an enormously important role how to distribute this enormous future radio telescope across the globe.
We all need to be grateful for all the people who are on that panel, and there weren't many.
We have two in the room.
And the other thing she shares in common with just the umbrella now is that she gave the length the GMC lectureship, if I can get it out.
So the Jetski Lectureship marks the achievements of Karl Jetski, who was the first man to detect radio waves,
extraterrestrial radio waves and launch the subject of radio astronomy.
So it's my great pleasure to introduce Jacqueline van Goal.com to give the 18 10c lecture the role of gas in galaxy evolution.
Thank you, Roger. So can you hear me? Yeah. OK, so my visit has already been fantastic.
Thank you very much for this invitation. It's a wonderful opportunity and I have to confess I've never been to Oxford, so it's just amazing.
It's really been very nice and I hope it will stay nice. So it was really good.
So today I want to talk about the role of gas in galaxy evolution.
Now you might think that gas is only a tiny part of your galaxy.
And so maybe it's not that important, but it actually means galaxies need gas to grow.
So I actually, although in Konia, I was a radio astronomer, I worked actually on star formation, not in neutral hydrogen gas and galaxies.
But when I moved to the field, I actually started emitting somewhat of neutral hydrogen galaxies.
And this is the image that really got me going. So this this is a picture from the L.A. Times.
We made the news. And what you see here is this is a galaxy.
We put the lights down and this is the galaxy is about the size of the Milky Way.
So there's a huge galaxy there and what you see here are the stars. Now what you see around it is the neutral hydrogen gas.
And so that shows that if you just used to looking at optically in a visible look at the stars, you actually see only a tiny portion of the universe.
Galaxies may have a lot of gas around it. And so when I saw this picture, it was in the early 80s.
I said, I want to make an H1 image of the universe. And so that has been my goal since then, and I haven't gotten very far yet.
But today, I'll tell you a little bit about this, these efforts.
So. So this was a very old fashioned view.
We saw this neutral hydrogen. Nowadays, we know that many galaxies have, or maybe most have, a huge reservoir of hydrogen around us.
So this is now again, this is sort of the size of the Milky Way.
Right? It's tiny. It's just the stellar disk. And this is all the gas that we now know is around it.
So that gas is in many different phases.
It's only nice to test different temperatures and some of it is neutral and so that gas might and might get recycled.
So the Milky Way might throw out some gas and it might fall back later, or it can be excreted from the gas that is in between the galaxies.
And so today, I really want to talk about what happens, how galaxies get their gas so it might fall in and it might help sustain star formation.
And sometimes they lose the gas or they lose this reservoir around it.
And that's kind of star formation and they stop and they become red and that galaxies.
So this will really be the story of my talk.
Now I have to say a little bit about neutral hydrogen because they're actually not many people working on this topic,
although right now there is a big renaissance going on. So the neutral hydrogen and hydrogen is the most abundant element in the universe.
Of course, neutral atomic part is much smaller than that, but there is a lot of it around.
And so if you you want to observe it, you have to make a big effort because the line emission is very weak.
I'll get back to that. But just to know the actual content of a galaxy is not enough to say what's happening to that galaxies.
I think that it's really making the images of the distribution of the gas and looking at the kinematics tells you what is really happening.
And so I've been working on this for many, many years. And right now there is, as I said, there is a big renaissance going on very soon.
So there's many different instruments that can do this work much better than the original archery, which I've been using until now.
So there will be a lot of work on hydrogen imaging.
So these are some of the instruments that are coming online.
So first of all, there's a telescope in India that is like to very nurturing and has also just been upgraded.
It's an amazing instrument. And then many new telescopes come online, escaped meerkat and aperitif that will do similar work.
So in the very near future, you will hear a lot more about this topic.
So why is it so difficult to measure this neutral hydrogen line?
It's very simple. It's a highly forbidding transition, so you have few.
This is sort of the shell structure of an atom.
So the ground state of neutral hydrogen atom, there's proton and an electron, and they can either have parallel spins or opposite spins.
And so if the electrons flip spins, it emits a tiny bit of energy.
It's the 21 centimetre wavelength and it spins so that the wavelengths I observe it is radio telescopes.
So just twenty one centimetre. And you say, Well, how often does this happen spontaneously?
It happens about once every 10 million years for a given atom.
So what a waste of my time to spend doing this. But so fortunately, if you look at the galaxy, there is many, many atoms.
So in a typical column of atoms at any place in the galaxy can be 10 to the 20 atoms.
So that is why you can actually do this observations. And so that's what I do.
So I'll show you here one picture of the fairly large array telescopes.
As Roger said, I'm in the early, early 80s, I arrived actually two months after the instrument came online.
It was very exciting times. So it is a synthesis radio synthesis interferometry.
So basically, since this wavelength is so long to get enough angular resolution to see detail, you need a very large telescope.
Now, you cannot make a telescope that is the size, say, of Washington, D.C.,
which is what you would need to get the same resolution as the optical wavelengths.
But what you can do is you can combine signals of different telescopes and use it as an interferometer.
And so this is an interferometer with three different arms.
And so if you wait eight hours, this arm have moved here that'll move there and that RF moves there, so you trace out a circle.
And so that is like simulating a huge single dish and the feeling is even more special.
So you can take these telescopes and move them out to different distance.
There's a railroad own way, so you can actually go all the way to these mountains here that.
Sets to resolution show the longest baseline is 30 kilometres, and you can combine all this data to make one image.
So that's I will mostly be talking about results obtained with this telescope.
OK, so what for me?
The big question is today is not so much. How does the gas move?
But how do galaxies grow in the largest scale structure of the universe?
And so I'll show you some pictures of that.
So if you look at the sky and you look at galaxies with a telescope, they are not uniformly distributed on the sky.
But in fact, you will see that there is a very distinct, intrinsic, intricate web of galaxies.
So you see filaments, you see clusters where many galaxies get into thousands of them and there is huge empty regions.
And so this has been known for quite a while, both from theoretical simulations and from observations.
And so the question is now what happens to the galaxies if they are at different locations in the cosmic web?
So that's what I will be talking about. So here is the result of a simulation, and this is just this is at four different times after the Big Bang.
So this is a simulation of only dark matter. So in case you don't notice, most of the universe consists of dark matter.
We don't know what it is, but there is a lot of it there. And so the theorists really love making simulations of the distribution of this dark matter.
It's actually pretty simple to do. You just know the laws of gravity.
So this is very shortly after the Big Bang.
The distribution is very, very uniform. It's very smooth. But then when you move on in time, you see that big holes develop and filaments.
And so here this is the current time.
So again, this this distribution of dark matter, you see that a fairly large empty regions, which we called for it actually knew by distance.
About 95 percent of the local volume is Foyt.
And so here is where the filaments get together to form. Clusters of galaxies might be thousands of galaxies zooming around very fast.
So this is the dark matter.
This is not to make the simulations of the galaxies in this dark matter is more difficult, but this is the distribution of the light.
So that is so again, the galaxy to form follow the dark matter.
And it's it's very clear now how do we know this is this?
So I'll actually show you first one simulation from the A-lister simulation just to give you.
Some idea of what a 3D structure looks like,
so I'll just show you part of it and start out by showing the dark matter and then at some point it moves to showing the hot gas in this.
So first you see these filaments form here and they grow bigger and bigger.
So this is. Very shortly after the Big Bang, 1.2 million years after the Big Bang, so structures built up to become more massive.
You see a very massive structure built up, this really grows can be a cluster.
And then at some point I did switch, and it shows the gas in here, and so then green will be the coal.
The gas and hot will be as gas gets really heated up.
So here you see those gas in these filaments and can be very low density.
But here there could be explosions, either supernovae going off or 18 feet back,
or it can be clusters colliding with large amounts of the gas get heated up to very high temperatures, like 10 to eight or something.
So just give you basically some idea of what the structure of the cosmic web looks like.
It's very, very intricate. But so we'll download talk about is what the galaxies do in these structures.
So how do we know that all this is happening? We have actually observations that show that this cosmic map exists.
So this is now a two-dimensional slice of the universe.
And what you see here is this is distance from us.
So we're going back in time and the yellow points are all the galaxies.
So if we know that the distance to the galaxies, we actually see that they are arranged in these filaments and into regions in between.
Then if you go to larger distances, you see that these patterns repeat.
So the structure is the same everywhere. So these voids have don't change in size.
They all are about the same. So this is what the the real universe looks like.
This is what you see. OK, so now I want to talk a little bit about how galaxies form,
and I'll basically give you a very brief recap of what a lot we've known for some while.
So originally, when people started talking about this dark matter, they thought that galaxies grow by first.
They have dark matter falling into halos and then the gas falls into this.
Halos get heated up to about the furious temperature, and then it slowly cools and sellable in the disk.
That's how you make a galaxy. And then by merging, you grow the galaxy.
And so it turns out that the picture, which lasted until the early 2000s, was a little too simple.
We now know that gas falls in along filaments, and sometimes it doesn't actually get heated up to the fuel temperature.
But it is what is called cold mode accretion at full straight to the disk of the galaxies.
And so now we think and this was, of course, already predicted by James php.ini in 1977.
But now the simulations show that too. So what you see here?
I don't know if you can see it actually very well. So this is the cold mode accretion.
This is the accretion rate accretion rate density, and here is time.
So this is very early in the universe. Galaxies grow mostly by in4 of gas.
And then if you come to more recent times, the bigger halos get this effect that the gas get heated up and then settle slowly by cooling.
So hot mode accretion becomes more important here, but you still see that cobalt accretion is very important.
And then at the current time, you see that there is still an important part of mode accretion,
but it's only especially in special halos and the special locations.
And so what a prediction is, is that this you will see this.
Only in the lower Miss Galaxy, so the smaller galaxies might still be growing by this circumpolar accretion,
here you see the mass of the galaxy and here you see that around 10 to the straight unstinted 10.
The warm moat accretion start dominating.
So for the smaller galaxies, it's still important to have cold mode accretion and this is galactic environment.
So this is the density of two galaxies around your galaxies.
And this is the lowest density environment, is this voice.
And so what you see here is that in forest, you expect actually that this cold mode accretion might still dominate.
So I will first tell you something about observations of galaxies and voids, and then I'll go to galaxies in very high density regions in clusters.
And then finally, I will tell you about a survey that we are doing with an upgraded fealy through a huge slice of the universe.
So let me first tell you about for it. So these are the most empty regions in the nearby universe, and it's really in the local universe.
What I'll first be talking about, because that's what we've been doing for a lot.
So we there's a big optical survey of the entire sky.
It's the Sloan Digital Sky Survey. And so we have two distribution of the galaxies nearby and so into it.
We selected the first image region, which must be had to do a little bit of mass.
We had to smooth the galaxy distribution and then find out really then to diffuse this.
And then we had to find the largest distance from the filaments or the deepest densities in the fields.
And then we looked and you said, if there is a galaxy we imaged and see what each one looks like.
So here it is. So this is this is basically a distribution of the galaxies.
And this is the density field that we derived in it. And then this is the distribution of the lowest density.
So if you have wide and means it is furthest away from the filaments.
So what you see here is so to pick these are really deepest under densities in the field.
And so if you look at one of these places, boom, you find a galaxy and that is what it looks like.
So that is how we did it. So then we observed a whole bunch in about sixty four, which we observed galaxies in these voyage.
So here you see, this is the black is the distribution of the galaxies.
Red is the distribution of the density field, and this is the galaxies we observed.
And so we actually did this with a new back end at Westerberg telescope that you could probe a large instantaneous velocity range.
So if you look at a galaxy, we can also see galaxies at the larger velocity and at a lower velocity which are
in the filaments and that forms the control sample for the observations for it.
So what two galaxies in four voids looked like?
So people usually don't talk about it because there are so few galaxies, but they are the ones that are there are really interesting.
So they're all very small, and most of them are blue, which means they are forming stars.
OK. And so for those of you who know more about Galaxy, so if you look at the distribution of all galaxies in the nearby universe,
for example, we slow and you look at the colour versus the luminosity you find at the galaxies are distributed into groups.
There's the blue cloud.
They are forming stars and then the this is the blue cloud and the more massive galaxies are in what's called the red sequence.
So the red dots here are our first galaxies full.
And so what you should notice is that all the galaxies are really small.
We have no galaxies that are larger than three times 10 to 10 solar masses.
Instead, they're all small, but I do spend the whole colourings, so we have actually one red Ford Galaxy.
OK, but it's what is really interesting in these galaxies is the distribution of the neutral hydrogen.
And here you have it. So this is here.
You see an overlay of the neutral hydrogen contours on an optical image.
And so what you see is for this just an example, these four galaxies, they all have very extended neutral hydrogen envelopes,
which is so I think a typical galaxy in a slightly higher than city region would usually have a smaller extent,
but still so much larger than the optical extent. So now have you two hydrogen envelopes?
And what so since we observe hydrogen one at a very specific wavelength, you also get the distribution of the motions of the gas.
So Doppler shifts out of the gas moves towards us that get the wavelengths get a bit shorter.
If it moves away from us, the wavelengths get a bit slower. So these are the falsity fields of the neutral hydrogen.
And so one of the most interesting galaxies, I think, is this one.
And here you get the blow up of this. So this is happened to be the first galaxy.
The image that neutral hydrogen was immediately a big hit.
So here you see the optical image. It's tiny. It's a very small galaxy and it's rotating like this.
And this is the neutral hydrogen envelope, so it's sort of perpendicular to the optical image.
And actually, it is rotating perpendicular to the stellar body.
So this is what you would call a polar disk, and this has a lot of very interesting properties.
So first of all, there's more mass in the disk in neutral hydrogen than there is in the stars.
And second, this galaxy is a very thin, tiny galaxy.
It doesn't have a bull's looks totally undisturbed. So and then third, we have been looking very hard to see if there is any stars in this.
So we did very deep V observations. There's nothing there.
It's just gas. So and here it is.
This is a position for city profile. So there are no punk counterparts.
So we think the tidal, if this would have been tidally created, it would have stirred up the stellar part of the galaxy.
So it hasn't. So we think this might be an example of smooth accretion of gas.
It's not disturbing the optical at all, which is bingo. That's what we hope to find.
And here you see the location of this galaxy in the cosmic web.
So this is the orientation of the matrix axis of this galaxy.
So it is very close to a very small filament.
And what we think is happening, if you look at this poll on this is that the gas is flowing out of the forehead onto the galaxy,
which was just what was predicted by some people who do simulations.
So this is a simulation of gas flows in it and here a filament.
So we think that the gas is still creating the galaxy is still creating gas out of the void.
OK, so now there's other interesting things it.
In fact, our galaxy is close to one of the largest force we know about in the universe.
And so there is in that void. There's also a tiny galaxy. It's called Caking two, four six, and it's sort of similar.
It has. So you'd say it's one envelope that is slightly misaligned with the galaxy, so the major axis are not quite aligned.
And if you look carefully at the velocity field, you see there are some irregularities in it.
So we think again that this might be an example of a galaxy that still has the following in.
OK. And another interesting thing they found in this point is that if you look at one galaxy,
we found that there was actually a whole filament, a very thin filament of gas.
And there are three galaxies in this filament. And I'll talk more about this velocity structure later.
So several people have now been finding filaments in for it,
which is again something that you expect that later on you have a void and then within there you form new filaments.
So this is another example of that. So the conclusions from this sports survey were that by looking in for it,
I think the most important thing is you select an interesting sample of galaxies, not all small there might all be accreting.
They have very little miss simplicity, many of them. So these are galaxies.
You are just looking at a low density part of the universe and the galaxies are still growing, slowly growing.
So I think that's very, very interesting. And we have actually some other indications that void galaxies are fascinating.
And I just want to show you this. There is a famous astrophysicist in Princeton, Jim Peebles,
who has always been pointing out that there is like me, something's wrong with this Leibniz KDM.
And what he pointed out is that in our local group, the most massive galaxies are actually not in the highest density regions of the galaxies,
which is which is what you would expect if galaxies grow by merging the most massive ones to should go to high density.
And so he said he had already three galaxies. This is the Super Bowl plane.
And here are the three galaxies that all of you astronomers know well and two six nine four six
M1A1 and fifty that are really in very low density and NGC six nine four six is important.
It's really in for it now. I like this.
So as an aside, John Garamendi pointed out that all these galaxies have no real boulders that have pseudo bulges, so they haven't been merging.
And still, they're big. But if you are an H-1 astronomer, you know something else about these galaxies, which is that there's a six nine four six.
This was one of the first two examples where here you see the optical and now in yellow, you see the H1, which is much more extended.
So this one galaxy in a fault.
So if you look at the very regular velocity field of this, guess that's way outside the optical and you take a slice through here.
Then you see this gas follows a very nice rotation pattern, except he boom.
It's shifted by 50 kilometres per second and here the same and here the same.
So the idea is there are holes in the disk there and the guess is really displaced.
So already most mine in 2007 said that it looks as if stuff is falling in.
Now there's several examples of that where this has been noticed a long time ago, and no one has guessed displaced by 150 kilometres per second.
And we don't know how it got displaced, where it could be because stuff is still falling in.
So what I want to say is that it seems that there are galaxies that become
latent and are still growing because they have gentle inflow of gas and the H1.
So some of the sectors that now recently a very interesting paper appeared on the results of a Arecibo survey of over.
But it also looked at force and what they noticed was that in it, they find filaments and what they call tendrils, which is the same thing.
So what they noticed was that in these filaments, the galaxies grow bigger than they normally are,
and they look undisturbed and they keep forming stars. So they're not going re-emerging, but they're probably going by in full of gas.
So, so grateful for it. So now I'm going to completely switch topic.
I'm not going to the highest density regions of the universe, and so I'm going to look at the nearest cluster of galaxies.
And so a cluster of galaxies. As I said, there might be thousands of galaxies.
They move around very, very fast and they are filled with very hot gas like 10 to the eight degrees Dimension X ray.
And so the question is what happens to these galaxy clusters? So in clusters, we often find galaxies that have completely stopped star forming.
And so we have to find out what the reason is. One of the possible reasons is that the cold gas is being swept out by the hot gas.
So this is a picture that we made of the vertical cluster.
So what you see here is this is a picture of gas. There's only gas in this picture.
So this is the Virgo cluster and this is the hot gas. What's been detected in X-ray?
Yes, M87, which is the galaxy that the Event Horizon telescope imaged recently.
So there's a black hole in the centre now, but this is a big galaxy. So it's very hot gas around it.
And these are galaxies that we imaged in H1 one at a time.
And what you see is the H1 disks in blue, but they've been blown up by a factor of 10 so that you can see them.
Otherwise they would be. And so what you see is this picture tells actually a lot.
So one of the things you see is that closer to the centre, these galaxies have very tiny H1 disks.
Why further out there have a very large one disks.
So that suggests that if a galaxy falls into this hot get, it actually gets stripped of the Gold Coast.
So this is what we call Ramprasad.
Stripping has been discussed for decades now, but I think by now we have very good evidence that that is really what is happening.
And here you see some images of that.
So here you see galaxies in the outskirts of Virgo that have this galaxy actually has a huge amount of gas, very large envelope.
But then when you move in, you see here. And so again, the controls are neutral hydrogen and the image is the stars.
And you see this galaxy, for example, has no neutral hydrogen on one side of it.
And that is because it's falling into the hot gas. This galaxy is really interesting.
It has a totally undisturbed stellar disk, but the gas is being pushed out.
So that's what we call empiricist tipping.
So this is a way for galaxies to completely lose their gas and maybe lose that reservoir of gas and stop forming stars.
You see, other examples in these galaxies have only a little bit of neutral hydrogen right in the centre.
So these different mythologies tell us a lot about at what stage they are of stripping,
and we can now compare that to the stellar population synthesis to see when star formation stopped in this disks,
and we can actually derive what orbits the galaxies followed before they fell into the cluster.
So we've learnt a lot. And so one other picture that we made that we thought was very spectacular.
So here again is Feargal, and we noticed there is a whole bunch of galaxies all at about the Fiero radius of the cluster that if you look careful.
You see that I have tails in H1 here, you see them quite clearly, so this is a tail in H1 years until in H1.
That are all pointing away from a central cluster.
So we think that in this case, this indicates where RAM pressure stripping actually starts to be important.
So it's the gas that's very loosely bound in the outer parts of the galaxies.
And once they enter sort of the vireo radius of the cluster, they start losing the gas.
It gets swept out. But then if you go even further out, you see very long tails.
And so the question is, what is that the U.S?
Hundreds of killed parsec and so that can have different origins, could be interactions, could still be a Christian, could be stripping.
And so what I'm going to show you now is a movie that was made by Greg Bryant, who was in Oxford for quite a while before he moved to Columbia.
And it's just a simulation of the gas and what you will see us.
So it is basically what happens when galaxies fall into clusters.
So here we go. So if it gets wide, it means the density is very, very high,
so it's showing the density of the gas, so you see these galaxies falling in along filaments.
And then if you look carefully, you see that a lot of guts get stripped out of the galaxy.
But it felt full of holes. I hope you can see that.
So this galaxies are being stripped if they go once through the cluster, they mostly lose all the gas.
But in the in the filaments, you also see interactions and lots of things happening.
So this actually looks really quite similar to what we observe.
This is what happens to the guys in galaxies once again clusters. It's over.
OK.
So the conclusion of this is there's actually lots of different conclusion to this, but one is that repressed stepping plays a big role in clusters.
And actually, it also plays a big role in groups, probably and in halos of galaxies.
The smaller galaxies that fall into the halos of bigger galaxies might even get stripped.
You see some evidence of that in halo of our own Milky Way,
and quality of the data is now such that we can do simulations and compare exactly what is happening.
We learn about the stage of disturbing and the future of these galaxies.
OK, so now I want to talk a little bit about the future.
And so first, I want to show you this picture that I like, but maybe it looks into a pretty low quality picture.
But this is, I think, the start of making an H1 image of the universe.
This is a result of high pass, which is low resolution neutral hydrogen survey.
And what they show here is two slices in a universe at different philosophies, so one is further away than the other.
And what they show is that red is galaxies that are unusually poor in gas.
So to smooth over the distribution and blue is where there is an absence of gas.
And so I think these images, if we could make them just for the whole universe, at least for large trip, it will tell us a lot about galaxy evolution.
And I think for again, for the astronomers, the distribution of gas may actually tell you something about galaxy conformity.
So there is an observation that if you look at a big galaxy, the smaller galaxies around it are not forming stars.
Why is the galaxy become red? Because it's gas. So apparently not only that galaxy lost that gas, but the surroundings too.
And the opposite is true, too.
If you see a big galaxy that's still forming stars since blue, the smaller galaxies in the Earth are also still forming stars.
So an image of this could tell you why that is.
It's just the neutral hydrogen reservoir around the galaxy, so just the large scale distribution of the gas, possibly.
OK, so now I go to you. So this was all talking about the local universe really nearby stuff.
Now I'm going to tell you a bit about evolution. So what do we know about evolution of of galaxies?
And of course, so of galaxies? We know a lot. This is the evolution of the star formation rate and density in the universe.
And so this is going back to about half the age of the universe.
So this is redshift to you. And so you see that it peaks here.
And then since then to allow the star formation rate drops dramatically.
So in the last times, the star formation rate is dropping.
And so the question is, why is that so this is really well known? But what do we know about a neutral hydrogen movement?
So hydrogen is part of the gas reservoir. And so it could be that star is just galaxies.
Just stop forming stars because they run out of gas. But what do we know?
Not much. We know a lot about hydrogen density nearby.
Because it's easy road map to home nearby universe, and then we know it at very large, large distances,
but other hydrogen lines from the different excited little levels are shifted to the optical window.
So we know that here here.
So you see the Arabs here are actually very small, but this range between redshift zero and one, the error bars are enormous.
And that actually indicates that we know very, very little about what's going on there.
So the goal would be to try to observe that.
And so that's what I've been doing for the last six years or so it's been.
So this is an image of the H1 blind service that have been done so far.
So what you see here is the offer of our service and our receiver survey covers.
This is a fraction of the volume that a conference so nearby we know Will what whole sky.
But if you go further and you see here the distribution of the galaxies,
this cosmic map and you see there's one survey here and one survey here, that's the body survey that was done.
We're supposed to work. And so this is not what we are doing. So this what's called the Chile survey and this was a pilot.
So once we finish this, we go out a lot further and we know at least a little bit of what the galaxies to ultra large redshift.
So it's called the chillis survey, huh?
New Mexico has lots of Chile. You know, it's the Cosmos H1 large extragalactic survey.
It's thousand to our space, the very large array after the upgrade.
And it's basically it's sort of what a square kilometre array signed to be doing, but then much better and much easier.
And it was when I started it, it was a pathfinder to the pathfinders.
So right now, the past minutes are going to be a pathfinder for me, but that's how it happens.
So this is a collaboration.
One of the things that was interesting is that this is a really international collaboration, except there's nobody from Oxford.
But other than that, there's there's lots of different countries,
and one of the goals was to include people from all the past years that are being filled.
So I suspect you have heard of square kilometre array.
This is going to be this amazing telescope that will eventually come online and sort of a world telescope.
So when that plan was made to build that,
people started building smaller telescopes that would already do certain parts of the science with the escape.
And those are the past finders. And so all these collaborators are actually most of them are part of one of the past funders.
So there was sort of an interesting collaboration. So the main scientific motivation should now be totally clear to you.
It's I want to know how galaxies grow as function of location in the cosmic web.
So that's for me by far the most important. But of course, lots of one of the things you can do.
And but one. So this is an observation from redshift zero two point four five.
And it's just something I was pointing at one spot also. So this you can get morphology kinematics of individual galaxies.
You can get the distribution total of each one in the universe.
Lots of other things you can do. Um, so this is all pointing.
So the Cosmos field is one of the best observed spots on the sky.
So there's a large HST Hubble Space Telescope mosaic of this area.
And so it's being observed at every imaginable wavelengths, except a neutral hydrogen.
So we started doing it in neutral hydrogen and this is our pointing.
We are not pointing at the centre because there is a strong radio source that mess up everything.
So we just put it a bit off.
But the strength of this field is that there is all these other observations that can help with the analysis of what we do.
And so this is a plot of the sensitivity. So this is this alfalfa survey that was by far the most important in H1 until now.
So that is that is in the local universe.
These are different sensitivity functions. This is what we did in the pilot for this field.
So that goes to a redshift point, too. And.
This is the sensitivity that we get after some hours, so that goes to a rent of two point four five.
So the reason we could do this was because the feel, which for a long time was the most powerful radio telescope that was around was in the late 90s.
People realised this is electronics that is 30 years old so we can do much better.
So they're actually upgraded it. And so while I've been doing much of my work with men of a total of six megahertz, you can fool the pilots.
We could use 240 megahertz and now we use four and 18 megahertz.
And it means that we can properties enormous velocity range all at once.
And so since the the lines are so weak, you really want in one pointing to probe many, many galaxies.
That's the advantage that you can have this large velocity cover.
So you could early on, you could have said, I want to observe a galaxy a directive 2.5, but you wouldn't get a thousand hours to observe one galaxy.
But in this case, we observe a whole comet. So we can get many galaxy sets, one that is really what the upgrade is.
So that is that's what we are doing. And so we did lots of this, lots of interesting stories about this.
So when we started to feel I had a telescope, the field didn't have a computer.
Australia was building a telescope, but already had two computers.
So we said, let's work together. So we did a calibration in New Mexico, and we shipped the data to Australia.
And then Amazon came along and said, Could we use your data to demonstrate that Amazon is good for basic science?
And we said, sure. So we are still getting entirely free computing on Amazon quite a few years later, which is amazing, but it's been very, very nice.
So that's what's happening. So we're observing this thirty one thousand velocity channels.
And so first show you the summary of what we found in this pilot, which only close to half to Richard Franks.
So this is where the distribution of the known galaxies, which there was all this other data.
As I said, optical data, direct points are detections. And so this is just 60 hours old, really.
And the idea was that we wanted at the largest redshift.
We wanted to be able to test what we locally knew as the most massive age amongst galaxies.
So that's basically and that is also what we do for the larger survey.
So and so here you see a summary actually of some of these results.
So you see, this is a galaxy that is really nearby. I guess it's.
About a year, and it has a huge one envelope, it's very disturbed.
If you go to a larger redshift, you see interacting galaxies and this is a really good galaxy.
So already here you see that the morphology is telling us some very interesting things.
So that was good enough to convince the the time allocation committee of the field that they should give a thousand hours, which was great.
OK. So we wrote in our proposal about the expected detection radius, and we calculated that in two totally independent ways.
One was, we said, let's look at the distribution of masses in local universe and just assume that there is no evolution with redshift.
And let's see what the distribution will be in this whole column out to a redshift of 0.5.
How many galaxies will we detect? So that is this graph.
Another way is to look at all the spectroscopic things, known galaxies, and there is a relation between colour and size of galaxies and each one mass.
So we can look at the spectroscopic known galaxies and predict what each mass will be.
And so that is this curve and this is the distribution of the galaxies.
And so both mass estimates said that we should get about images of about 300 galaxies.
It would be great. We aren't there yet, but we hope to get that eventually.
So I'm not going to show you a few results of the first hundred eighty hours.
That's a big one. And so what we did was we said, OK.
In fact, I had a student who was about to graduate, and the student said, I really want to get some results.
So she wanted to look here. So we'll get it. So the first question is, can you inherit 80 hours?
Could you actually detect already galaxies at this redshift?
So at that time, nobody really had gone beyond about this.
They say we're no galaxies detected. So the first thing you can try is to do stacking.
And so this is stacking at two different redshift. So basically, you don't detect individual galaxies,
but you take the profile at the location of each galaxy that you know off and you shift it all to the same velocity and then you combine it.
And so this is taking a direct shift of point one to. And this is sticking a directive two point three seven.
And so lo and behold, he had one mass. So that is not the mean one mass of these galaxies about 1.8m central line.
And this is three times then nine. So this is sort of what we hoped we would find that to mean h one mass would go up this redshift.
Right? That is why just a star formation go down because they're running out of gas, so they should be more gas at higher redshift.
And I was in March, I was in India. And so there they have this time metre radio telescope and they actually got an amazing result.
They just started observing a year ago, they did the same same stacking game.
So this is sticking around redshift of one. And they find that the H1 mass is one point eight times 10 to the 10.
So it's really going up, and I think this looks like a pretty reliable result.
So this was presented at the conference, but I've been very, very careful.
This is a graduate student who did that. So this is the first, I think, reliable secondary result at a redshift one.
And so it is completely consistent. There also have a striking result at a rate of two point thirty seven, which is consistent with ours.
So there seems to be really an increase in mean H1 mass with redshift.
So we hope so that's that's the first result that's really interesting now since we are looking at galaxies and I told you endless amounts about that,
I'm so interested in pursuing that and actually being an undergrad who uses an algorithm to define the cosmic map in the Chile survey.
This snake luber. So he used this programme dispersing to define it.
And so we can now look. So one thing is he predicted, what four H-1 content we should see us see as a function of distance from the film,
once again taking into account all the limits, etc. So he predict that indeed, the H1s goes up.
If you go to larger distances from the filament, which is sort of what you expect if they move to the filaments,
eventually the galaxies get decoupled from the gas.
Right, that's the cosmic web detachment prediction.
But so we can now they find this cosmic map for the Chile survey.
And so these are results for a pretty low redshift.
So the red dots are the galaxies that we detect.
And so, for example, this is a galaxy that's the most isolated galaxy.
It's the fourth galaxy. And you see it has a huge one envelope, which we really like.
And so one of the things I'm really excited about,
which we did last week is so the simulators and actually the several people here in Oxford
to be doing to predict how galaxies will get formed with respect to the filaments.
So if you have a filament that just collapses and is still thin, then it collapses from two directions and expensive to search.
So you expect the angular momentum of the galaxy to be perpendicular.
So the spin factor to be aligned with the filament two rotation is perpendicular.
So the prediction is that the smaller galaxy spins that are aligned with the filament well.
Eventually, the bigger galaxies will start merging, and the spin factor might change.
So these are all pretty small galaxies. And what you see here is the so yellow is the orientation of the filaments.
And if you look to the next to it, so I guess you can see it much better.
Is this in yellow is the spin factor of the galaxies.
And so if you make a histogram of the alignment, then you find that eight out of 10 are actually what you would call a light.
So I think this is very cool. This is the first time this has been done in H1, and so eventually we will get 300 galaxies we can do this with.
So that's that's really interesting. So now I come back to this filament that we found in Floyd a long time ago.
So this is the three galaxies that we found. And so if you look at the velocity fields and you know how to interpret velocity fields,
you see that for the three galaxies to commanders, here they flip.
So it's rotating in this way, and the spin factor will be aligned with Finland, and that's true for all three.
Optimists believe this. OK, so now, as I told you, I had one student who wanted to read it, and she said, I really want to discover something.
So she looked at the wretched points, seven assists he may not. And she looked at all the galaxies that were predicted to have a large one mass.
And so she detected this galaxy in neutral hydrogen.
And so then this student immediately went to the large millimetre telescope in Mexico and looked for seal.
And he finds odour. So this is the first detection of data on a emission directed mission at a rate of two point three seven six.
So this is a fantastically interesting galaxy. So first, the H1 mass is three times and then it's very massive.
The H2 mass is five times 10 percent. So ridiculous. It's really massive.
And so here you see, this galaxy was known from its starburst and galaxy, its form of stars 80 solar masses per year.
It's a massive galaxy. The stellar mass is eight times 22 percent, which is sort of interesting.
So if you look at this more carefully, we say, Well, OK, is this galaxy unique in terms of its properties?
So it is gas originated from, but here you see distribution of stellar mass versus H1 mass.
And so the grey is the alfalfa found.
This is our galaxy and here are of what they call H1 monsters.
So those are very H1 rich galaxies. So it is gas rich, not unique.
But now when you look and see, oh here again, results of different surveys,
then it turns out it's only sort of the only other galaxies that have so much seal are from this FIPS survey,
and that is a survey of galaxies at much higher redshift. So these galaxies are the richest one.
So to see oh, content is really, really unusual. It usually in an utter way, and that is its star formation rate.
So this is the star formation properties of galaxies, a function of stellar mass in the local universe,
actually redshift point five to see this is our galaxy, it's forming stars way too fast.
But though, if you look at Galaxy said at a redshift between 1.5 and two, you see that it fits right in.
So this galaxy and its properties looks like the galaxy at a much higher rates.
This is just again what we hope to find. So is one of the first results of chillies.
That's really interesting. And of course, since I'm talking about spins, I asked again to look at a cosmic map around this galaxy.
So it turns out this this H1 is aligned with a filament.
And so if you look at the spin of this, if this galaxy, the spin is perpendicular to the filaments, so which is it's a big galaxy.
So maybe that's just what some people expect. It's not aligned. It's been going for a while, but it's a fantastically interesting galaxy.
So from this galaxy, you can say the first Asian image is it looks like it's a galaxy.
It's very gas rich, very instrumenting.
It has an unusually really unusual light SEO content, and it looks more like a clumpy disks they you see at higher redshift.
So this might be near by example, but we can actually start studying that.
So this is the first step to making a neutral hydrogen image of the universe.
And so what can we conclude? So do I guess so? Conclusions and more questions?
So I think one of the conclusions very careful is that maybe we find real evidence that the H-1 content of galaxies is increasingly stretched.
We have no number of independent measurements that seem to suggest that.
And it was already known that the molecular gas content of galaxies increases pretty rapidly and especially the ALMA telescope.
Amazing results on that. So one question is, is the ratio of molecular gas to atomic gas changing with redshift?
And so the indications that it is and I think one of the big questions is why is that and by how much?
So this is really fantastic. So those are the conclusions.
And I just want to end by telling you that we really live in interesting times.
And the reason is that there's all these past findings that have started taking data.
In fact, here in Oxford, there are amazing results using a telescope in South Africa and Meerkat Telescope, it is one of these past findings.
It just started working. It's working better than anybody expected. It's really amazingly good.
So this will go much deeper and will and has a much larger field of view.
So there will be a real survey of H1. Eventually, I'll do a redshift of one, and ESCAP is an Australian up activists in the Netherlands,
and they will both do a very large area of sky of nearby galaxies.
So I think once these guys have got a data, we finally can maybe understand how galaxies grows at function of the location and of course, them.
And then there's the square kilometre array, which will image galaxies attractive.
And so we have to be a little patient, but eventually it will be there and it will be fantastic.
So that's it. Stay tuned.