16:01:05 Well welcome everybody to the October meeting.
16:01:11 The open meeting of the Royal Astronomical Society.
16:01:16 This meeting is taking place, as you'll realize viral webinar.
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16:02:06 And it gives me very great pleasure to introduce to our Darwin lecture for this George German lecture for this year. Dr. Philip out front anally Philippa front anally is professor of gas dynamics and the evolution of galaxies at the captain astronomical
16:02:25 Institute at the University of hiding in the Netherlands.
16:02:29 He obtained his PhD from the University of Milan yet in Italy, where he was the assistant professor between 2006 and 2017.
16:02:40 He did postdoctoral research both in the Netherlands, and was also a Marie Curie fellow at the University of Oxford in the United Kingdom.
16:03:03 He's published more than 100 scientific papers on various astrophysical topics, and he is co author of a textbook.
16:02:57 Introduction to galaxy formation and evolution, published by Cambridge University Press.
16:03:04 He's a recipient of the Friedrich Phil Hellmuth vessel prize of the Alexander on humbled Foundation, and of course also receiver of the ward of our George Darwin lectureship for this year is me great pleasure to ask Filippo to give us his lecture.
16:03:22 Thank you.
16:03:25 Thank you very much about this very nice introduction, let me share my presentation. Maybe you can confirm that everything is fine.
16:03:36 And you see where.
16:03:42 Good. Thank you.
16:03:43 Thanks again to the Royal Astronomical Society for giving me this great honor to present you this, George during lecture Desir my lecture is going to be about how galaxies, and in particular, spiral galaxy is like the beautiful example that we see here,
16:04:05 gather their gas, and why this is so important for the revolution.
16:04:11 I have 700 other people to thank.
16:04:16 For what fundamental contribution to this work, but I will do this in the course of the presentation.
16:04:24 So spiral galaxies are also called these galaxies for the obvious reason that most of the visible matter is distributed in this rather thing discs that that's essentially constituted by stars gas in dust, and the Milky Way is one of them.
16:04:46 So, understanding the formation and evolution is a particular interest for us, but also is facilitated by the fact that we are inside one of these parent galaxies, as we see this lecture and spiral galaxies, and also start forming galaxies in the sense
16:05:07 that they, they, they have active status would mention today.
16:05:13 And this is very clear from an optical image like this one where you see sites of star formation, very clearly were effectively cold gas is collapsing into the formation of new stars.
16:05:36 And this cold gas is actually one of the main character of this lecture. So, let me introduce you to the distribution of cold gas in this nearby galaxy, as seen using the 21 centimeter.
16:05:51 Initial line that shows the location, and also the motion of neutralizing as we discuss a bit more later. This image was a thing with the vegetable agent that is in the Netherlands and what you see it immediately the two images are on the same scale is
16:06:09 that the gas is also distributed in the disk and the disk is our state is even more extended than the spell of this.
16:06:18 Now, the story that I'm going to tell you today, started long ago.
16:06:25 Quite a few years ago when I was doing my PhD, and I was studying this spiral galaxy and NGC 24 three.
16:06:35 And this gives me the opportunity to thank the first person who was fundamental for this work and also I must say, extremely important for the beginning of my scientific career transition cheesy was my PhD supervisor and within, we were studying the cold
16:06:54 gas in this in this spiral galaxy 24 three.
16:07:00 And what we found is that the coal, gas, was not just located in this disk in rotation around the axis, but there was also some gas neutral gas above and below the disk that at that time we call the normals the US and now this is called an extra layer
16:07:21 of gas.
16:07:22 And this was particularly interesting because it had a peculiar kinematics, in particular, it was rotating more slowly. it's updating more slowly than the gasoline, this battle by this result that we this discovery that we couldn't explain.
16:07:40 I, I can now take the next very important person that has contributed to the elite, and also to the later development on this work is Jean, James being, we know my head debris previous work in Oxford after my PhD.
16:08:05 And what we did, we tried to build the dynamical more than that will display these explain of gas. So if the galaxy, that is forming stops and this starts exploding a supernova.
16:08:17 They can eject lots of gas outside these and create to see the correlation which is called galactic founding. And this, we thought could explain the exoplanet gas.
16:08:29 This work quite well. But there was actually a small problem that actually was very important. The fact that the the rotation of the gospel of us me these galactic fans was was too fast, with respect to the observation.
16:08:45 And the difference between this observed rotation and the predicting rotation turned out to have profound implications for galaxy evolution as I'm going to explain this lecture.
16:09:04 But before going into that, I'm going to take a step back and going to explain a little bit in very simple terms, galaxy evolution formation and.
16:09:15 So, the formation of galaxies in the universe can be seen as a journey of almost 14 billion years from gas the gas to the present the galaxies. And actually this is a Jordan a from a very simple type of gas, because the primordial gas was essentially
16:09:35 made the chemical elements to most important. I do need you. And while now, we have a variety of structures, not some character, all the chemical chemical elements that we know stars that Blackboard planets, and at least in one place in the universe,
16:09:54 life. So how do we go from this to that, that is another ingredient that actually is quite important. And unfortunately we know very little about it and that entity is the dark matter that is driving the evolution of galaxies.
16:10:11 And this is represented by the simple sketch here, where I'm showing the so called Dark Matter halos, which are gravitational potential winds at the bottom of which the broader galaxies and then later, the galaxy, new angles.
16:10:33 And what is happening continuously throughout this evolution is that new material is coming in, into the dark matter radio from the so called intergalactic medium.
16:10:42 And this material is both made of dark matter, and gas.
16:10:48 And this is feeling a medium inside the metadata that I'm going to put syrup from galactic me.
16:10:56 Now, let's concentrate on the galaxy that is the very center at the very center, that is,
16:11:06 for reasons that I will discuss later cold gas and the by cold gas. I mean, gas at a temperature that is such that can produce the formation of stars so star formation is the is the main process that is taking place there, and the formation of stars of
16:11:30 course is building the stellar component of galaxies very important, but is also consuming the gas, because because gas is disappearing into the stars.
16:11:41 And this, as we will see later actually requires a continuous replenishment of the gas with gas or condition on to the very center so in the disk.
16:11:54 Moreover, South formation produces of the chemical elements as we said, but also, especially true supernova explosion produces that economical supernova feedback, which gives us the other direction of the flow so the got the gas outflows from the disk,
16:12:12 into the external environment.
16:12:15 Finally to complete the picture essentially every massive galaxy, we know today as a center of supermassive we call it black on that also can release, lots of energy in the media, and this we call it Blackboard feedback.
16:12:32 Now, this is actually, especially from the point of view of the gas and Floyd any theoretical picture because guessing flow, and gas accretion are very difficult towards.
16:12:45 Fortunately, though, the main consequences of gas exploration in ultimately is the formation of stops, so we can use the formation of stars to infer the property of gas, and the blood that I'm showing you shows the average rate of star formation in galaxies
16:13:09 in the universe as a function of time, automation. As you see me know.
16:13:15 And this essentially tells us that the Stanford measure rate.
16:13:32 And this essentially tells us that the Stanford measure rate. On average, was higher in the past, iteration to was about 10 times is that today that is c zero, but also tells us how much gas is being consumed to form starts and we can use this to understand
16:13:37 whether there was enough gas in galaxies, or gas exploration was needed at all times. And one simple way to see the desecration was in fact needed is very calculated calculating the gas depletion time, because the patient time simply, the ratio between
16:13:56 the massive gas that is in the galaxy, and the star formation ways of the galaxy, and it tells us, for our long a galaxy can go on farming starts with the available gas.
16:14:28 And what comes out as you see from this figure here is that the depletion time on average in galaxies is all with as always being outdoor that one, even less.
16:14:17 In the past, but now I just told you that the universe is 1314 billion years old in some galaxies and formed stars throughout the world the age of the universe.
16:14:37 So, this one legal alien tax us that necessarily this guy, this the supply of gas as be continuously repair and it's by God's creation otherwise would have stopped falling stars at the very beginning of devolution.
16:14:53 Okay.
16:14:56 However, there are some galaxies web stopped for the stars, we call them, Dave, we say that they have quaint their star formation, that is in fact that they caught me of galaxies between blue galaxies that the spiral galaxies that I discussed before.
16:15:13 They are very ice affirmation late, and they are blue because young stars tend to be blue and red galaxies, which have essentially noon or very low star formation rate, usually a red galaxies I wasn't different morphology is the elliptical as the cord.
16:15:33 But there are also some red galaxies that are perfect discs as the world did you see from the point of view of the gas, the new galaxies are galaxies that have been able to gather new cold gas throughout the age of the universe.
16:15:52 When the red galaxies had lost their podcast, somehow, and, moreover, they've lost the ability to gather new guys.
16:16:01 And so this brings me to the first fundamental question that I will try to address in this lecture, which is why do some galaxies deep cold gas, while others don't.
16:16:16 Now, I want to go a little bit deeper into the gas equation, and being a little bit more quantitative.
16:16:25 And to do this, I'm moving to the making way because underneath the way we have an enormous amount of information in particular we can we can reconstruct the star formation needs to receive the, the, the density of star formation as a function of time.
16:16:44 Very well. And what you see is, is a lot of this stuff. The Stanford measure rate and find some time with respect to the present day which is zero yet again.
16:16:56 And we see that also in the Milky Way the Stanford mentioned in the past was much higher than the present time was higher than the present time, it was actually the only effective to i, not, not much.
16:17:07 And we can use this information now we're building a simple model of evolution to reconstruct, how much gas was needed to form the stars and effectively to reconstruct the gas accretion rate that can produce this star formation.
16:17:30 And this is what in business shore near and you see that also the gas the commission rate was increasing in the past, but not much because more or less the gas accretion rate is only one or two, sort of solar masses period.
16:17:48 Finally, in the Milky Way, we can do more, because we can look at the chemical abundance of stars in these. And through this chemical evolution models, we can actually learn a number of things about the accrediting material.
16:18:05 First of all, we learn that there has to be a condition, because as you see this closed box model, that does not have gas the condition, Mrs completely the feet of the data.
16:18:17 So the second thing though that we learned we said, type of gas, it is, is a greeting to, to build the seller component that we seen Milky Way, as also should also have a relatively low chemical abundance, which we call it, Middle East, the low Middle
16:18:36 East, the metal poor gas.
16:18:39 So these are two fundamental things that we learned.
16:18:44 Now the question is, we need all these gas equation that is then gas available to to be accretive in the disks. And this, and to do this we can look at the distribution of matter in the verse, and I start from the distribution of all matter that quantifies
16:19:03 And I stopped from the distribution of all matter that quantifies dramatically our ignorance, with respect to this, because 85% of the matter is in the form of that matter, and we still do not know what is made of my let's concentrate on the ordinary
16:19:17 But let's concentrate on the ordinary matter, which can balance the 16% that we call cosmological body infraction, and let's break it up, if we break it up at the ratios zero so today we discovered that only 5% of the available ordinary matter is being
16:19:34 turned into stars, very few. The universe is being extremely inefficient at forming starts.
16:19:52 While the gas in galaxies is even less on the 2%, the vast majority of the ordinary matter is in the form of gas that is outside yet is either in the secret galactic media or in the intergalactic menu.
16:19:56 So the answer to the question is yes, there is plenty of gas to feed star formation and galaxies in the, in the universe and, in, in throughout the devolution of the universe panels today.
16:20:13 There are two ideas about the way gas and flow and accretion take space into galaxies that go under the name of cold called flow and hot flow in the causing flow more than the gas can actually reach the disc of the galaxy in this call for what we call
16:20:34 do we mean something that to some of you maybe doesn't sound very cold but in this in this terms is can be considered call this time around, 10 to the four key.
16:20:47 Okay, degrees. And this type of a condition was very quick.
16:21:04 Any start to be important direction.
16:21:04 In the hot inflow keys.
16:21:04 Instead of having this cold filaments that are coming in the Gospel. The discovering it settles in this very hot medium degrees atmosphere. Okay. At that point, to accreting the datacenter in the galaxy the gas this hot gas has to cool because you cannot
16:21:18 form stars out of medium degrees. Yes, but this cooling may be problematic because this gas as a very long cooling time. This is an important point that we'll discuss later on.
16:21:32 And the general idea is that there is a critical mass and below this critical mass is about five times 10 to the lemon so that surpasses all the dark matter a lot of the galaxy, if it got it see if the Halo is below this mass, then maybe that can be still
16:21:52 calling flow, especially a direct ship. If it is a ball, there is the formation of this hot.
16:22:14 Halo, that we call also galactic Corona, and the question then is there, can the gas be cool to feed the star formation in this, or is this affirmation waste, at that point, and this is particularly relevant, if we look again at the history of the Milky
16:22:20 way that we think we can reconstruct in this in this manner.
16:22:26 And the Milky Way was born somewhere before rush, 10, like any other galaxies. It didn't look like that at all. It probably looked like what we see in this cosmological either the anomaly can simulations in simulation in which you see a very small galaxy.
16:22:47 That is acquiring lots of gas from the external environment, it also is bombarded by some supplies galaxy that are emerging.
16:22:58 So, the initially book, as shown also by its relation could be in the form of this cold inflow so filament, and these types of structures that are feeding the disk.
16:23:12 But then at some point, the mass of the able to meet the way grows with time.
16:23:18 As you can expect, and an elite is this critical mass. And so the for the rest of the Revolution, the Milky Way has a hot gas you see or hot Corona, and this actually happens, we estimate between one and two, but it is a nation one, to me, is it that,
16:23:38 this, this, this ebook in which the Milky Way is a hot deal is a very decent very long time. Because we are talking about something of the order of 10 billion years in.
16:23:51 So it's a physical space is a very large fraction of the age.
16:23:56 Moreover, what's most interesting is most of the stars in the Milky Way, and formed in this ebook, and just put it in context this son was born dead right.
16:24:07 And just to put it in context this son was born dead right. So this brings me to the second fundamental question that I will try to answer in the rest. In this lecture, which is how did spiral galaxy keep gathering code gas in this heart.
16:24:22 a lot of people.
16:24:23 Okay so this now brings me to the core of the lecture itself, meaning the explanation of this mechanism of fountain accretion.
16:24:35 And so just to recap, we have said that these are surrounded the gas was discussed surrounded by these extra plane and gas, and this is a plane and gas could be produced by the Galactic fund, but how do we see this in reality, and they beat to me have
16:24:56 kind of phenomena, is this galaxy, and you see an 891, who is conveniently oriented precisely edge on with respect to us, and we have observe it in optical as you see here, but also in this age one emission on the neutralizing, and this gives me the opportunity
16:25:22 to thank, neither fundamental contributed to this work, who is Thomas a lot, who is a.
16:25:34 C'mon guy the things that award the master of data reduction and has produced this fantastic data that is shown for the first time that the neutralized region is actually extended that up to 5010 PTC almost everywhere above and below the disk.
16:25:53 And now this is the end this, we think is partially produced by the ejection of material from the disk. But this is not the story, because as I said before, we don't see it in this image, but we can see in, if we, if we look with other type of things
16:26:16 but let me use this animation to make the point, this galaxy and this simulation of the fountain is going on in the middle of this very hot atmosphere.
16:26:29 So, when this relatively cold gas because this is each one is the gospel for 10 two to four or less, the Calvin degrees. When these gases ejected, and it necessarily interacts with the very hot gas, and this one what happened, it will be something that
16:26:52 is similar to what you see in the simulation. The clouds are breaking up, and the end it is a mixing of the cold gas that has been injected, and the hot gas, let me play the simulation again, because I wanted to concentrate on this turbulent wake behind
16:27:09 the cloud is forming and you see the theme this week. There are a number of the blue conglomeration of gas.
16:27:19 These ones and would be awfully, we can get him, clear later. These are condensation not where the guys that you see that doesn't necessarily come from the cloud itself, but it comes from the condensation of the hot gas that is cooling down very rapidly
16:27:42 and becoming blue that in this case is tend to default. As you can see, degrees.
16:27:49 And in fact, this received medically at least when we look at the evolution of the cold mass in this type of simulations and we see that the code mass is increasing with time.
16:28:01 So, the mixing between cold gas and hot gas is the beginning, the cooling of a fraction of the cost of the hot gas, and this is Sean, Clearly, in, in this in this sketch here that you may have seen before.
16:28:20 When, when we see that in in within the fountain cycle, there is, there is this the formation of this mixing material behind the cold front of the cloud.
16:28:33 And in this place is where the call the condensed gas for forums, and the reason why forms, is that the the cooling time that they are leading a time of the art gas was very long aggregate here and even more than once a year, but the cooling time in the
16:28:52 week. So, after the mixing of hot gas and coal and gas, you can imagine the cooling time decreases dramatically down to 10 mega year so effectively part of the podcast is cooling and coming back to the desk.
16:29:08 Together with fountain site.
16:29:11 Does this work in reality.
16:29:14 Well, a phenomenal like this. There are a number of phenomena like these that work here reality. I'm giving you an example here, that was at the very origin of the Industrial Revolution.
16:29:29 So these new cannon steam engine of 1720 is a very similar type of phenomenon, there is there is steam that is pushing the beast on, up until that the red van via opens and injects cold water into the steam this produce the condensation of the scene and
16:29:53 to be some comes down in the cycle.
16:29:58 Restart.
16:29:58 In, in galaxies we think there's something very similar is happening and possibly at a much lower rate.
16:30:07 So this was discovered by another person I like to think, one of my former PhD students for the decoding it in the paper in 2010, and was done with simulation VDI the solution on doing this case into the two parts of the solution.
16:30:29 And this resolution I want to stress is particularly important because you need passive resolution to start the phenomenon, therefore not phenomena like mixing and conversation.
16:30:43 In, in dismantled cycle.
16:30:46 And I like to point out another result that for the legal thing, in, in, in another paper where they looked at the exchange of momentum, between the fountain cycle.
16:30:59 So these, effectively, the cold disk and the hot around, and he made the prediction, because these two are interacting with each other.
16:31:12 The hot gas. A predicted estimated date, but it will take the land, with respect to these come about 75 kilometres per second.
16:31:27 And.
16:31:27 Five years later, actually, the rotation of the hot gases the Milky Way was measured. And it turned out on door with very large to be very much in line with the prediction.
16:31:40 Then, after these early simulations, we, we have produced many other war with simulations and I like to mention, really the last one that was, was done by a master student in groaning and and Mike was doc Dr.
16:32:04 As as go to Toronto. And in this case, we have, we have Phantom cloud that you see is, is pushed away by the wind that we are we are changing the reference system but the process is the same, but the most important thing is this simulation includes many
16:32:21 very complicated effects and not only that I did cooling but also magnetic fields and isotopic thermal conduction, and they are always farcical solution.
16:32:33 And the.
16:32:35 The interesting thing that we find is that also in this case, the mass of coal and gas increases with time, meaning that is condensation and going decision is in fact desired solution simulation consistently predicted.
16:32:49 And there are several other authors now, they're finding the same resolved. Also in different contexts, for example doors of galactic winds variable, but these are only simulations, you may say, next to see if there is evidence of this code really going
16:33:09 on in galaxies and and to look for this I have to go back to NGC, nine one.
16:33:16 I was said. I said that then you see no one, as all these extra planar gas.
16:33:24 Like, several other local galaxies but I said that this doubling of gas, we're talking about cold gas.
16:33:32 The temperature, that I was describing before. Is this a planar gas rotates, more slowly than this but I didn't give you the evidence for this. The evidence is showing this plot to this is simply NGC a man one rotated, and we end the points in this block
16:33:52 to showing the rotation velocities above the desk for KPCM over these down near five k PC above the desk. In this case, and you see that this this notation is much lower than the rotation of the disk, that is in this dashed line appear.
16:34:13 So the southern gospel days most lonely but what you also see is a fountain loaded, so the simple know that that I was describing at the beginning and I was saying that this predicts the gas utility faster than observe and daily when you see that the
16:34:29 fountain over the exultation by a large margin, essentially everywhere in the disc.
16:34:36 Why is this happening to understand why is this happening we have to look at the trajectory of clouds that they've injected from the disk in the founder model, which are shown here in this movie on the left, you see that all these clouds are going up.
16:34:57 and going to the outer parts of the Halo, and then falling down to the disk at the landed video.
16:35:06 And in this, this, this plot that I'm showing here, there is no interaction with the hot gas, so the fountain is moving in a vacuum and essentially what drives the motion here is so called the gravity.
16:35:23 And obviously they are conserving anger because of Israel, makes the velocity and I'm showing the defy of the component of the clouds in the exoplanet layer in in red, makes the velocity remain more or less than that, at the same level it as this velocity
16:35:42 which the disc speed which is this rotation of speed, which is this black curve.
16:35:50 Now we go to a completely different model in which the particles are interacting, like in in the fountain of creation.
16:36:04 With the external hot meal, and they are pulling this medium. So now the code gas is not represented anymore, only by the particle by particle, plus, this week, where there is x.
16:36:17 Halo material that now is schooling and coming back. And because the hot gas is rotating more slowly. This movie modifies the orbit. And as you were you were seeing there is, there is the radiant motion that is produced, and also when you look at the
16:36:34 rotation. These particles are all rotating significantly more slowly.
16:36:41 So this essentially tells us that there is an imprint of the condensation of the hot gas in the kinematics of of the cone the extra gas, and this imprint is characterized by two aspects, the notation, and the slippery slope.
16:37:03 So when we go to implement this for the model of NGC 891, you see. Now, this blue, blue curve, which is Phantom blast the equation of the corona into the fantasy cycle reproduces the data very well.
16:37:19 But not only.
16:37:20 We can also do to add this, this, this production of the absurd rotation. We also have to input a certain attrition rate because more condensation would lower and lower the velocity of discipline or gas.
16:37:42 And the interesting thing is that we find the effect of the data for an acquisition rate, which is very much of deal or there possibly a bit lower than the star formation of this galaxy.
16:37:56 So this essentially means that the fountain accretion mechanism, not only reproduce the kinematics of this airplane of gas that before we couldn't reproduce, but also triggers a condition of the course oh nine so cooling condensation, including of the
16:38:21 at the rate that we need to feed the star formation galaxy. This model was developed further by another XPS a student of mine was now postdoc in Florence, and Selena Marasco who applied it to the old sky age one data way again, called gas.
16:38:41 And, and this this this in this plot here, I'm showing what they call the longitude the velocity plots. This is a relatively complicated work because you have to look at.
16:38:55 Phantom models from inside. And what Antonia did he created the mock observations of the models, and then compare them directly to the observation, the actual observation that you see here in this last corner, and you can buy you can see already that
16:39:11 the second column year was better than the first column, which is the bureau found in London, but if you're doing statistically, you can actually obtain a very precise value for the best fitting accretion rate that you need to reproduce this this result,
16:39:33 and this turns out to be about two solar masses per year. So the fountain is circulating continues the eight sort of masters video. But when the clouds are coming back, that they are bringing the eight that has been ejected last two, that is coming from
16:39:52 the cooling of the corona so we are gaining continuously gas, gas for the future star formation in the galaxy.
16:40:01 And let me remind you that the information needed in the Milky Way to feed this the gas equation needed in the Milky Way to feed the information is essentially precisely to sort of necessity.
16:40:34 spiral galaxies.
16:40:36 They are still not many but you have to realize that, to see the exoplanet gas we need to sleep the deep observation so this is exactly that goes extremely deep.
16:40:46 And so we don't have these observation for many galaxies. And once we found the year, we, we, we had the, we, we did the kinematics and feet of this this galaxy so this is not the dynamical model, yet.
16:41:01 But what we found is that the kinematics of most of these galaxies, that is the plane and gas is is perfectly compatible with what we expect from the fountain occasion, in particular, that is this location, and that is this radial flow that you can see
16:41:19 as essentially the oldest point of the article Borland sort of radio velocity, negative.
16:41:53 And this essentially Texas the local spiral. The disappear gases Lucas fire seems to show this evidence for fountain accretion type of kinematics, and the dynamical model is in development, and these the work of another PhD student and silly at the campaign's.
16:41:53 company's. Finally, moving towards the end of this talk, I would like to mention other three results that are very much related with with Dr. Taylor and now we conclude with, with a depiction that is emerging from on this, the first result is as been
16:42:15 obtained by whichever doctor was also a PhD student of mine, some years ago and she is now putting stuff.
16:42:26 And she looked at the effect of condensation for different temperatures for the hot gas, and what she found is that as you move away from the temperature of the Milky Way, which is about two times.
16:42:43 10 to the six to 2 million degrees, and you go and you move to higher temperature, the efficiency of condensation goes down dramatically, essentially, already for four times as six there is, there is no conversation.
16:43:00 And this is essentially due to the form of the cooling function, because the Milky Way or even colder hottie and those are very close to the peak, while.
16:43:13 When you move to higher temperatures you're very far away, and essentially the cooling time does not decrease this bit the.
16:43:23 Despite the mixing with with cold gas, this, this is potentially quite important, because, as I said, I must galaxies tend to have high fever temperature, could be because of this inefficient accreting gas through Phantom accretion.
16:43:45 And the second work that I would like to mention is work done by Gabrielle soli was my PhD student, some years ago, and now is fan of the campaign Institute, and he looked at the angular momentum of the accurate in gas without assuming any galactic fountain.
16:44:05 He essentially started with this iPod This is, which is the following. If, if you ever rotating this and, and it is material that is accredited onto the disk so forth into the base, but it enjoys the disk with a different specific angular momentum locally
16:44:27 with respect to these, and especially in Nowhere to. This is bound to drive radial motions. This
16:44:38 is unavoidable. And, and in particular regular flows. Now, what Gabriela found is that this effect, as, as profound implications for the Middle East, the gradients in galaxies.
16:44:54 So we, so it is the chemical evolution model, from which you can use the Middle East, the gradient absurd. For example, in the Milky Way. As you see, as a senior to reconstruct what was the specific angular momentum of the accurate in gas.
16:45:12 And what he found is that the accrediting material master for falling onto the disk with a rotational speed, which is 70 80%, the speed of the disc locally.
16:45:28 So, with the definition. And this means with the land of about 5075, kilometers per second.
16:45:36 Now, this is, as I said, it's not related to the fountain but during that you will remember this, this number from what I said before that this is very much the land that we expect for the hot gas, very close to the disconnect we think is accreting with
16:45:54 the fountain phenomenon. So essentially, these can be seen as an independent confirmation of fun to leverage.
16:46:03 And finally, I want to mention this work of Academy as a student, by always working on
16:46:13 social features in NGNPGN spectra that are essentially showing us the cold warm phase of the silicon galactic media, and in particularly I'm showing the detection of this medium around our neighbor, the Andromeda galaxy.
16:46:33 And what time today is to build the models of cosmological equation, to see if this cosmological recreations of coming clouds coming from the deja vu stores these can reproduce this observation.
16:46:50 kids about drama dies, beyond the classic to do this would take several Giga years. And interestingly enough, the clouds are probably not going to make, because they will evaporate coming down, as you see happening in this simulation here, they will simply
16:47:13 evaporate and disappear in in the corner, and they will not lead to the risk so this is not a mechanism to feed the disk of coal and gas.
16:47:24 Okay, though, then this is my concluding slide, which I'm trying to wrap up. All I've said in the second system picture. So, that is gassing flow from the intergalactic medium into the dark matter a lot.
16:47:42 And wherever these gases flow, at least for large fraction of the life of galaxies like the Milky Way. That's not feed the disk directly. It feeds the hot Halo to feed the disk we need something else because we have to cool this hot gas in the hot cocoa
16:48:03 in a look around the galaxy. And what we, we think is happening is that cooling is triggered by this fountain mechanism that I described as long as the galaxy has a cell phone disk, and can eject cord material that will mix with the hot in the NGO, and
16:48:27 this phenomenal wiki going until one of these things, things happen either the disk is lost, and that would stop completely the phenomenon. This could happen.
16:48:41 For example, as a consequence of mergers, or the temperature of the hot gas becomes too high, and so the conversation is very efficient as I said, this can happen because the, the massive the ego of the galaxy becomes I or or because that is a particularly
16:48:59 effective supermassive black hole or because the galaxy enters an environment with very high temperature, like for example, galaxy clusters. And so at that point, the galaxy becomes LA Galaxy, and loses the ability to gather new gas.
16:49:22 And so with this, I think I've tried to answer the two questions that they've said that those stages at the beginning, How did spider goddess and keep gathering good gas in the Otter Tail or ebook.
16:49:49 With this phenomenon of fountain a condition, and the condensation of the, of the hot gas. Why do some galaxies keep going gas, don't because to dad there's one of these three things is has taken place.
16:49:55 So this concludes my lecture, and I thank you very much for your attention, and I'm happy to take any questions you may have.
16:50:23 Thank you very much indeed for the most interesting lecture. Um, can we move to the questions, Louise course, and thank you very much for Philippe that was a really great talk.
16:50:27 So first question that I've got at the moment is Allison Lovejoy deLory. He was asking about the time scale of the developments which are being discussed.
16:50:40 And now I think so. I think the point at which that question was asked was during the part where you started to talk about fountain condensation so I'll just summarize the timescales from yours.
16:50:57 So, the typical cycle of the Galactic fountain.
16:51:03 He's time of the order of 10 to the eight years, few times 10 to the seven tend to be eight years. So it's, it's actually a relatively short time. That's why I was staying.
16:51:21 The. Even the Milky Way to one thing that I haven't, I haven't specified, is that in this extra planar layer, there is roughly 10% of the cold gas in the galaxy.
16:51:36 So, 90% is in the desk and 10% is in the plane at late, and to keep this layer there because the landscape is relatively short, you have to have a circulation, that is actually quite active, so that was saying, eight sort of masters video ejected continuously
16:51:54 in the Milky Way to keep this planet later that, but yes the times are relatively short. I hope this answered the question much. My catch the market man's has had a question, is the chemical abundance of the in flowing accreted gas as expected.
16:52:14 I mix of primordial and do.
16:52:18 So, we know, not so much about the metallic city the chemical abundance of the hot gas that is surrounding galaxies, the estimate that we have, go between point one to point to the solar.
16:52:41 So, relatively metal pool but not extremely metal pool but this is also due to the fact that this is gas is relatively close to this so there will be some pollution that is taking place so it isn't.
16:52:57 It is certainly a mixture of material that is coming from outside. Probably most of it, and also somebody that is coming from the disk.
16:53:07 Thank you.
16:53:10 Stephen King is asking, why does hot Halo gas rotates more slowly than the disk is the accumulation of gas slowing galactic rotation.
16:53:23 So okay, the first question.
16:53:27 Essentially, The, the hot gas.
16:53:32 In principle could even not have a day to talk, because, because it is so hot that can be sustained that its own pressure so you can be Nigel started in the room with the pressure.
16:53:46 Then, then from this statement you can understand that the.
16:53:50 If there is a notation this notation doesn't have to be the only mechanism that is keeping the gas there, so it can be lower than the, the rotation of the disc, the disc completely essentially rotation and support your thesis place the first question.
16:54:15 emulation of gas.
16:54:18 Electric rotation, this is a, this is an extremely good question.
16:54:25 So, in principle, this would be a worry. But actually what is happening in our models is the following, is that it is true that the gas is coming down as a lower rotation with respective disk.
16:54:42 But this gas is not coming down in the center of the galaxy, these gases coming down at a relatively large ladies, typically 10 kilo passing from the same.
16:54:54 And this is very important because then even if the patient is slower, the actual specific angular momentum of the material, which is RV. So, the there is the radius involved is actually higher than the than the angular momentum of the disk so this type
16:55:14 of phenomenon can actually increase the angular momentum of disks in long timescales and produce the inside out growth of discs, that is, this is observed, and respected.
16:55:36 This
16:55:37 Yeah, there is another part to the question that I've missed actually which was does temperature of the hot Halo control the rotation speed of the desk.
16:55:52 Not a not sure I understand this question, because the rotation of the DS is very much determined by effectively, the distribution of matter. So the disc, the disc, we are talking about into this we're talking about the rotation of cold material.
16:56:18 So, gas, the gas attend describing as a very little pressure support so the rotation, that is determined by the distribution of the math of visible matter and dark matter which keeps the flat rotation curves for most of the disk size and then the increase
16:56:37 in the center and possibly increasing the outer path, we actually never see. So, I'm not completely sure I understand the question. Sorry.
16:56:57 I think we've probably just got time for one more question, and we've got a question from Belinda Wilkes. How do you determine the accretion rate of the cold gas falling back onto the desk.
16:57:04 Does it include original mass of cold gas in the ejected cloud, and the hot gas, which has been called and comes into the depths.
16:57:15 Okay, so what when I talk about the, the accretion way, that is coming to the desk.
16:57:21 I mean, the essentially only the part that is condensing from the corner from the hot gas. Okay so, so that is that is the part that we are interested, because the Phantom cycle, define that cycle, to some extent, I don't want to say anything available,
16:57:43 but let's say is the relevant because, because the gas goes out and comes back was out and can smack maybe comes back in a different place, but, but the the galaxy may lose the ability to use that gas for a little bit, as we said the timescales that are
16:58:00 but then he gets it back, because, because it comes back somewhere else.
16:58:06 But the bottom part is the part that is cooling and coming down.
16:58:11 That is fresh, new guys, that is then used for the future star formation and that is the gas equation we are interested in. So I'll do we calculated we calculated.
16:58:25 Trying to reproduce the the kinematics of the, of the extra planar gas, because the, the, given that they're creating material as a relatively low rotation, you can imagine that the more you, you make the the cooling efficient, and the more the rotation
16:58:45 of discipline or gas will do that. But our data tested the efficiency here, so once once I'm reproducing the rotation, I have the activation rate that that I need to reproduce a rotation.
16:58:59 And the important thing is that the same that you need for to reproduce a rotation is the same that apparently we need to feed this information.
16:59:10 Thank you very much, Philip or unfortunately we're out of time for questions now.
16:59:15 But it was it was a great talk I'm going to hand back to Mike Edmonds now.
16:59:22 Just thank you so much for the clearly explained, and I must say beautifully illustrated and presented Talk. Thank you very much indeed much enjoyed. Thank you very much.
16:59:32 Thank you.