08:05:02 Welcome you back to our eight week festival of CGM knowledge Katie's fundamentals of gaseous halos, and this week is the week where we discuss how this gas flow into galaxies.
08:05:22 So we're, you know, there are still two and a half weeks of knowledge to come.
08:05:34 Next week is how the gas is Hell's effect galaxy evolution. And certainly the previous two weeks should prepare you well for how gases halos affect your solution because I've been talking about how this gets filled out of galaxies, and how it flows into
08:05:43 galaxies.
08:05:46 We have a featured conversation that's going on this week we're trying something different.
08:05:53 Rather than having an after party this week and Halo 21 AGN.
08:06:11 We're asking for asynchronous participation, where we'd like people to go to the halo 21 agent channel and share their thoughts on how agents interact with the CGM, and I've posted some questions over there and that channel things you might want to consider
08:06:16 talking about.
08:06:17 One of the reasons I thought it might be interesting to have this conversation this week, as I said, is I think of the original CGM een CGM inflow interaction is the subject of cooling flows, which is decades old, and in more recently, we've tied ag ends
08:06:38 into that feedback loop. And so over in Halo 21 AGN is a place to discuss these issues.
08:06:48 Also, in the last 24 hours, there have been three new, new results submissions, one by Stephanie Tennyson one bite and Lou, and one by Alex Cameron. So I invite you to go.
08:07:03 I don't think they're all up yet on the YouTube channel.
08:07:06 But you can already view those videos over a new results on slack.
08:07:13 So are to to really have to tutorials today and it's come to pass that we have to. And so we're going to space them out a little more than we've been doing it partly, maybe to give people a little more breather but also because I know it's very least
08:07:28 the two speakers, want to participate in each other's discussions.
08:07:33 two speakers, want to participate in each other's discussions. So we're allowing a little more space.
08:07:37 So, near member car is going to go first to talk about physics and cold streams. And then we're going to have that discussion time run until 9am Pacific, and I set up adjusting case breakout room, in case we do need to, if that discussion is still roaring
08:07:57 along, and we decide we need to continue it we can switch it over the breakout room that discussion is going to happen in the main Zoom Room until it needs to move on to tutorial to Jonathan stern talking about physics of hot accretion and cooling flows.
08:08:15 Right. So, without further ado, I want to introduce Neil man Tucker who I guess is in the process of moving from Santa Barbara to Israel is that correct, yes, where you are, where are you right now, and spirit I'm in Santa Barbara
08:08:38 and farm I'm slightly further north in California, but I met KTP at the moment. So we're tweeting affiliation. Yes, okay.
08:08:50 So I'll stop sharing my screen, and I'll turn the screen, over to you. So we can all learn more about cold streams.
08:08:58 Thank you. Can everybody see the screen here.
08:09:05 Looks good. Awesome.
08:09:08 Thanks Thanks so much, Mark and thanks so much to all the organizers I've been having just the best time, so far, and I'm very excited for the next couple of weeks.
08:09:20 So yeah, I am currently at KTP though next fall I will be going back to Hebrew University in Jerusalem to begin a faculty position there.
08:09:32 And it's my great pleasure to tell you a bit about work that that us and several others have been doing in the last several years studying the physics of the cold streams that we think feed the most massive galaxies at high redshift, and specifically
08:09:48 the interaction of these streams with the ambient hot certain galactic medium in these halos.
08:09:56 And I want to begin with just a bit of, kind of, you know, context by what we mean by these cold streams this came up a little bit during the discussion.
08:10:06 Following yesterday's keynote talk so this is an image from a cosmological simulation of kind of two very massive halos five times 10 to 12 so the masters at redshift, you know, to the snapshot and Z of four and what you can see here is basically all
08:10:21 the components of the cosmic web and how galaxies form within the cosmic web so what you're looking at.
08:10:28 by several very prominent dense elongated intergalactic filaments that are all co planner and all the black circles are every Dark Matter Halo in the simulation that has a visual massive bug tend to the nine silver masses.
08:10:54 You can see that for the most part they tend to lie along the filaments along an individual filament, except for the three or several most massive halos which like the nodes have several cosmic filaments, and therefore fed from the intergalactic medium
08:11:11 in a non tropic way from a few discreet directions, and once these intergalactic filaments actually penetrate the visual radius and begin to supply guess within our gear down toward the galaxy, we would commonly refer to them as cold streams or cold accretion
08:11:28 accretion streams. Now kind of as a rule of thumb, what galaxies do we expect to be fed by these a few discrete cold streams as opposed to galaxies lying along a given filament.
08:11:40 A good rule of thumb which kind of goes back to Declan Barenboim oh six is that it's a two sigma peak in the cosmic density field. So you can see here that's basically demarcated by the black line whereas all the colored lines are average mass tracks
08:11:56 for halos at different masses that Richard zero. So for example at Richard zero you really only expect, very massive groups or clusters to be stream fed at redshift of about, you know, to you expect any Halo above 10 to 12 solar masses to be stream fed
08:12:12 you would expect a milky way progenitor to perhaps have been stream fed at redshift for, or greater, and it's quite plausible that even a low mass dwarf galaxies if you go back far enough in time to reach six or above.
08:12:26 They were likely also stream fed long at the nodes of the cosmic web in this fashion so this is indeed a phase that we think almost every galaxy went through at some point during their evolution.
08:12:39 Now what happens when these intergalactic filaments actually do make it all the way toward the galaxy.
08:12:44 I'm going to show you now a movie, showing the evolution from Richard six to rich for kind of a massive star forming galaxies and cosmological simulation, this has a halo mess of two times 10 to the 11th still the masses that Richard six, and this is
08:12:59 three streams, which in this case, at least seem to actually make it all the way toward the central galaxy. Although we'll discuss that, and a lot more detail.
08:13:10 You can see here the three streams which are all co planner and seemed to be spinning up the galaxy supplying the galaxy, not only with additional gas if you will start formation, but allowing it to grow its angular momentum in a coherent way and there's
08:13:22 been a lot of work written about how cold stream accretion helps galaxies grow in terms of their I'm angular momentum.
08:13:45 You'll also notice that as the streams hit the disk they seem to drive a lot of turbulence in the disk and put puts puts this galaxy in a state of what we call violent disk instability where you have lots of dense clumps forming a strong turbulent motions.
08:13:46 So it's quite clear that the streams are, if they make it all the way toward the galaxy they're going to be very important in setting the gas content of galaxies the angular momentum content of galaxies and the turbulent content of galaxies.
08:13:59 You may have noticed that here the stream seem to have disappeared by the end. The only reason that they seem to have disappeared, is that the.
08:14:07 There are really two reasons the interaction region where the stream seemed to mix and join the galaxy has grown to be on the scale of the plot, which is set here to fix plus or minus 20 kilowatts, and also the plane of the streams is not always aligned
08:14:20 with the plane of the central galaxy. And since the plane of the image is here focus on the plane in the central galaxy. If the stream plane has been slightly tilted with the strength of that plane that would also make the stream seem to have gone away.
08:14:31 Now that kinematic signature of streams flowing in as we saw an inspiring toward the central galaxy. There are suggestions in observations of the CGM of very massive galaxies in high red shift that seemed to be at least consistent with that picture and
08:14:46 I'm showing here some results from a work by Chris Martin, using the KCWI, looking at lyman alpha emission of halos of few times 10 to 12 solar masses at Richard two to three.
08:15:00 And you can see this large scale kind of hundred kilowatt sick rotation signal or at least sharing motion signal in the lyman alpha mission of the Halo, and there's been a lot of work done.
08:15:11 Also some work in absorption about how these kinematics signatures are at least seem to be consistent with the image of inspiring cold streams from the various scales down toward the central galaxy.
08:15:25 However, the thought that these streams are able to actually make it all the way down toward the central galaxy, especially in very massive halos which we've heard a lot this week we expect to have a stable hot phase, a stable accretion shock with the
08:15:39 low temperature. It's not at all clear that streams can actually make it all the way down toward the central galaxy and indeed they may very well break up or be disintegrated due to hydrothermal or gravitational instabilities do do shocks or collisions
08:15:54 between streams in the central what we call, kind of like the messy region or the interaction region which is typically sphere of order 30 to 50% of the variable rate is.
08:16:04 And there's been a lot of work using different cosmological simulations that produce different results about how far into the halo the streams were actually able to penetrate and similar to everything else that we've been hearing about the small scale
08:16:21 structure in the CGM cosmological simulations are not really the best tool to use to study this because the resolution that they achieve out near the Halo is really quite bad only have ordered 10 or 20 cells per stream diameter so we can't really use
08:16:36 them to model the detailed physics of the evolution of the interaction of streams with the CGM.
08:16:43 And in addition to the general question of how deeply into halos two streams reach and how much can they supply galaxies the gas and angular momentum.
08:16:56 We mentioned the alignment alpha emission in the halos and one very interesting question is, could that be directly due to the dissipation of gravitational energy of streams, as they flow from the view real radius down toward the central galaxy.
08:17:06 It was been hypothesized that the gravitational energy gained by streams as they flow down the potential well, would be enough to basically power the giant lineman alpha Nebula or giant lineman alpha blobs that are so commonly observed around these galaxies
08:17:21 hybrid shifts. However, the details of that dissipation are not exactly clear and nor how it would depend on other Halo properties or if indeed this could even work.
08:17:31 So those are really I would say the two big main motivations for studying the interaction of streams with the hot ambient CGM, which leads to the following cartoon of Kelvin helmets instability in streams.
08:17:45 So imagine that we have a hot variable Halo with a temperature of order Tim the six Kelvin streams that are of order. 10 before Kelvin.
08:17:54 And if we assume that the streams and the halo or an approximate pressure equilibrium, that leads to the first of several dimensions numbers that define the system.
08:18:03 In this case the density contrast between the stream and the background which we'll get back to the back to the numbers in just a moment. The second dimension is number, defining the system is the Mach number, which is the speed of the stream divided
08:18:15 by the sound speed in the Halo, and since the variable velocity is of order the sound speed of gas, the variable temperature, the Mach number of the stream with the strength of the Halo is of order unity, which implies that the stream is going to be very
08:18:34 supersonic with respect to itself with Mach numbers in excess of 10.
08:18:34 And the third dimension was number that defines the system with only the physics we've talked about so far only hydro dynamics and cosmology, is the stream radius divided by the variable radius which is another way of saying the sound crossing time of
08:18:47 the stream, divided by the variable crossing time of the stream the time it takes it to make into the Galactic disk. Now all these parameters can be constrained by cosmology and in fact just to reiterate if you assume that the Halo is that approximately
08:19:00 virile temperature, the streams are at approximately 10 to the four and you have approximate pressure equilibrium between stream and the hot Halo, you can derive the density contrast is a function of the Mach number, and, and, and the redshift.
08:19:13 If you then take this density contrast and you have a model for the halo density near RV or, and the free parameter of what the hot gas mass fraction at our via would be, you can actually derive the mean volume density in the streams again as a function
08:19:26 of Halo mass and redshift. And then once you know what this actual volume density is assuming the streams are flowing at roughly the visual velocity and we know the accretion rate on to Dark Matter halos from cosmology.
08:19:40 If you have an assumption of what fraction desecration is Lama given stream, you can constrain this our stream divided by RV, and for example, for three times 10th the total solar mass Halo at redshift to you expect stream densities of order, tend to
08:20:03 minus two hydrogen atoms for cubic centimeter which is quite high for what we usually think of is the CGM, and our stream over RV or border 10%. Now what does this imply for the stability of the streams or the or the revolution, you can actually derive
08:20:08 what I'm plotting here as a function of this three dimensional is numbers density contrast the Mach number and the radius of the stream compared to the visual radius, the number of holdings of growth in the linear regime within a vehicle crossing time,
08:20:31 and the two takeaways from this plotter number one for a large region of the expected parameter space, these streams should be highly nonlinear Kelvin helmets instability as a lot of time to grow.
08:20:44 And number two, which is somewhat interesting you'll notice that there seems to be kind of a phase transition in the dispersion relation going from very fast growth to somewhat slower growth that has to do with an interesting transition Kelvin Helmholtz
08:20:55 instability in general going from what are known as surface knows which what we all study in our fluid mechanics classes, and are indeed caused by the sharing of two independent surfaces.
08:21:09 Compared to the body mode so at Highmark numbers, these Kelvin Helmholtz roles actually stable out due to the strong sheer, but what is becomes actually destabilized our sound waves reverberating basically back and forth between the two sides of the stream
08:21:23 and due to constructive interference growing the density and the pressure perturbations from the inside out.
08:21:30 Just to give you a sense of what that would look like because I think these movies are fun. What is killing helmets look like in a three dimensional cylinder.
08:21:37 So this is the evolution of a surface mode that has a density contrast of 10 and a Mach number one. And this is kind of what we're all used to thinking of I think when we think about killing helmets instabilities, the two sides of the stream here act
08:21:50 independently of each other, but all you do is up the Mach number to do those modes are stabilized at this point, and the way the instability grows instead is again through these sound waves reverberating back and forth in the stream growing kind of a
08:22:05 pattern of density pressure from the inside out and we know how to, how to model all of the different
08:22:13 growth rates. So, that was just the linear regime we already said well chemicals is going to be highly nonlinear so what is the final nonlinear disruption and streams actually look like well that looks a little different in the surface mode regime versus
08:22:26 the body mode regime and the surface mode regime you grow those Kelvin Helmholtz Eddie's rolls from each you know surface and they begin to slowly devour the stream from the outside in, through what can be modeled is kind of a diffusion process and you
08:22:39 can model that analytically obviously it scales as a stream crossing time it's going to be shorter, the narrower the stream is the body modes behave a little differently what you actually wind up doing is developing a very long wavelength sinus soiled
08:22:54 perturbation across the entire stream that typically has a wavelength of order, 10 times the thickness of the stream, and that eventually leads to very rapid generation of turbulence in participating disruption of stream in a timescale that also will
08:23:10 scale is the sound crossing time of the stream so, and actually both cases, the nonlinear stream disruption will be shorter for narrower streams. And this allows us to develop the largest stream, which is normalized where the deer ladies that will be
08:23:26 completely non linearly disrupted in less than a variable crossing time and again depending on our two dimensional numbers density conscious in the Mach number that can can change but as a takeaway message I would say if a stream is narrower than 5% of
08:23:40 the visual radius. We expect it to be completely shredded and destroyed in the CGM through hydrodynamic instabilities.
08:23:50 However, I haven't talked about any other physics what happens if we add cooling.
08:23:53 Well, as we've heard a lot about in the first few weeks through all the great work that's been done by all our friends Maxim Pang, searching Drummond Martin Vickery about the cloud question problem once you add cooling to the mix, you have to think about
08:24:09 a fourth dimension this number, which can be thought of in this case is the ratio of the sharing timescale so the non radiative sheer layer growth time to the cooling time in the mixing region, which can be translated to a stream radius divided by a critical
08:24:23 stream radius, and for cosmological streams if I use the same model that we introduced at the beginning to plot this actual ratio is a function of handle medicine redshift, you learn that cooling is predicted to prevent stream disruption by Kelvin helmets
08:24:37 instability this ratio is almost always expected to be larger than one.
08:24:41 Now, in practice, what does that look like in the no cooling case what you're showing here results from two simulations of just a passive scalar to trace the mixing of the fluids and the case with like know cooling, you see that the stream tends to fling
08:24:53 material out into the background tends to pollute the CGM with stream material was the core of the stream remains relatively unmixed with cooling with strong cooling.
08:25:05 You see that that is not what happened to stream remains very, very animated and actually a lot of the background material has been trained on to the stream and is really mixed very efficiently into the core of the stream.
08:25:17 If you change this into the slow cooling regime, then I would hope you agree it looks very similar to the no cooling regime we're all that was done here is changing the cooling times.
08:25:28 You can see the same thing in the density so with, you know, I'm out cooling the stream density becomes very diluted as it flings material out into the CGM whereas with cooling the stream can remain very dense, well mix and very column aided, and with
08:25:43 slow cooling again You seem much more similar to the case without any cooling.
08:25:49 You can actually model, the mass and treatment, using similar models to what we've heard about for due to the cloud question problem.
08:25:58 And you can ask well by how much can the stream as grow in the CGM and it can actually grow by by by the factor of two or three in the simulation seemed to match the analytical predictions practice and treatment occurs through these turbulent mixing layers.
08:26:15 Now as a streaming trends material, it slows down this is kind of the opposite question of accelerating a cold cloud in a hot wind. So now he wants to decelerate a cold stream and a hot CGM by allowing you to train material.
08:26:31 And let's just do to conservation of momentum, and indeed the. We haven't, you can derive an analytical prediction for how the stream should slow down as a function of, you know, as a function of time.
08:26:43 That leads to dissipation of kinetic energy of the stream and it also leads to dissipation of thermal energy from the background as the background cools and condenses onto the stream.
08:26:53 So, you can put all of those and elements of the problem of the problem together dissipation of kinetic energy from the stream dissipation of thermal energy from the background and also include generation of turbulence in the stream and slightly heating
08:27:08 up of the stream both of those turned out to be somewhat negligible. And you can do the bookkeeping of all the energy generation and dissipation in the simulation.
08:27:18 That's what's shown on the left and kind of the left panel, and then the right panel is what the cooling function of the streams and the ambient CGM would give you at any given time step and the fact that the left hand panel and the center panel agree
08:27:31 with each other, means that all the dissipation mechanisms which we know how to model and are just due to this killed and helmets was cooling interaction are exactly what is fueling the cooling and the radiation so we now know how to model that.
08:27:44 And if you look at the distribution in terms of the temperatures, it turns out that most of that emission will be admitted in the linemen alpha through a thin layer around the interface between the stream in the background exactly through that Brady lovely
08:27:57 Lee cooling turbulent mixing layer.
08:28:01 And then, if you assume that we now have a stream in the, in the gravitational potential of a dark matter Halo, so it's accelerating toward the center of the Halo.
08:28:10 There's a density profile and the pressure profile both in the hot gas and in the cold stream, and also the stream is becoming somewhat like narrower as it approaches the center of the halo it's no longer a cylinder, but it's being kind of pushed into
08:28:24 a into a conical shape, but that locally at every given Halo centric radius, the models for kinetic energy dissipation and thermal energy just a patient that we derived for the uniform case can be applied.
08:28:38 You can basically derived quantity such as this, the velocity at point one RV or normalized with the visual of velocity, the function of Halo messaging redshift that by how much the stream mass has grown as a function of elements in redshift, and then
08:28:52 importantly how much lyman alpha luminosity has been emitted in the halo as a function of Halo mass and redshift. The upshot being that between 10 to 42 to 10 to 44 hours per second can be released from streams in the halo just due to this interaction
08:29:07 between streams and the certain galactic medium, which seems to be able to explain the at least low and intermediate luminosity lineman alpha blobs. I'm going to skip this discussion of oxygen six in the mixing layers in the interest of time, but I'd
08:29:24 be happy to come back to it during the discussion. If there's any interest in in the last two minutes if I may, I just want to say a little bit about self gravity streams can be modeled to self gravitating either thermal cylinders.
08:29:38 And the thing about a silver everything is a thermo cylinder is that it has a maximal mass per unit length, that it can, that it can have before hydrostatic equilibrium is no longer possible.
08:29:49 It's basically the equivalent of the jeans mass, but for a cylinder, instead of a sphere.
08:29:55 And, and this was given by Jerry Ostreicher 1964 depends only on the temperature of the stream through the sound speed. And if you draw this.
08:30:05 Our fifth dimension this number now the ratio of the mass period length of the stream to this like maximum mass per unit length or hydrostatic equilibrium, you learn that for a large regional the prime MySpace this should be larger than we should be should
08:30:20 be larger than one.
08:30:22 Now, in the star formation community we know that star formation in giant molecular clouds happens along filaments, and if any of those filaments has this new parameter larger than one that implies okay we know that filament should be forming stars sort
08:30:35 have gravitational instability. This would seem to be a prediction that cosmic streams in the CGM might be actually start forming.
08:30:43 And this seems to be seen in certain simulations so this is the same simulation that I showed you the movie of a few a few moments ago. And you can see here the dark matter, the gas and stars that are younger than 100 million years which is indicative
08:30:56 of star formation. And we're highlighting here two very dense clumps of gas that seem to be forming stars, but are not associated with any substructure in the dark matter and this seems to be consistent with the predictions of streaming stability, due
08:31:10 to gravitational instability. And we actually discussed that this might have some interesting implications for formation of metal poor globular clusters.
08:31:19 I also want to highlight this really awesome recent paper by Jake Bennett and Deborah see Jackie, who developed kind of a new and very fancy method to get enhanced spatial refinement on streams and there's simulation, and they also found that as the increased
08:31:34 the spatial resolution they found more and more star formation outside of galaxies in streams and this again might be indicative of this new larger than one stream which which should require some further study.
08:31:49 And in cases where the gravity, where this new parameter is less than one so you actually can beginning hydrostatic equilibrium.
08:31:56 But you still have now gravitational instability versus sharing instability of the Kelvin helmets instability.
08:32:04 Even if a cylinder has me less than one and it can begin hydrostatic equilibrium. That's an equilibrium configuration it's not a stable equilibrium configuration, it's still a lower energy state for the stream to fragment into discrete spherical clumps.
08:32:17 And the question is what is going to win fragmentation two discrete spherical clumps or shredding by Kelvin helmets instabilities. That's our sixth dimension this number, which is basically the timescale for this gravitational instability normalized by
08:32:30 the sheer by the sharing of time scale and this is work by Yale graduate student Han Han on at low basically mass per unit lengths when the helmet helmet shouldn't should when you see that the week gravity case looks like the no gravity case, except the
08:32:47 the central core of the stream survives for significantly longer because it's stabilized by actually due to buoyancy forces within the stream, which are basically parameter is by this Richardson number here, but at more massive stream still new smaller
08:33:06 than one so we can begin in hydrostatic equilibrium, but above the critical values so gravitational instability is stronger than Kelvin how much instability, you actually do form discrete clumps.
08:33:18 In the stream which while they're not self gravitating in this case they are actually pressure confined when you include cooling. These can become gravitationally unstable and start forming and will certainly affect turbulence generation in the, in the
08:33:31 disk itself. I'll skip MHD just to, we can talk about this in the discussion if we wished just to mention that this is of course the seventh dimensional is number, the plasma beta parameter.
08:33:42 So just to summarize cylindrical streams are kind of an intermediate case between playing with sheer layers and spherical clouds is a lot of very rich and interesting Physics for the pure hydro case sufficiently narrow streams can disrupt in the CGM do
08:33:57 to Kelvin Hamilton stability. However, once you add either cooling or self gravity, or MHD assuming still laminar flow for your initial conditions, cold streams do survive and the viewer to Central galaxy it's very difficult to get them to be completely
08:34:12 destroyed in the CGM cooling will lead to mass and treatment plus mixing might explain help explain lyman alpha blobs and has some interesting implications for collision the ionized oxygen six in interface layers self gravity can make the stream fragmentation
08:34:28 and star formation in streams which may be important for the formation of globular clusters at high redshift MHD which I didn't talk about might actually lead to magnetically dominated share layers between the stream in the background and kind of the
08:34:41 big open question is what happens when you combine cooling and so gravity and and HD and the halo potential. Can we come up with a description for the evolution of streams of the function of these now seven dimensional is numbers that we've talked about
08:34:54 the talk. And what would happen if the CGM itself were actually very turbulent and has strong shocks due to the visual accretion shock or galactic outflows which are interacting with the wind and again decidedly non laminar initial conditions, and I think
08:35:08 I'll end there and happy to discuss anything else. Thanks very much.
08:35:13 Okay.
08:35:14 Thank you very much.
08:35:16 That was already very instructive and we're going to have a bunch of discussion time.
08:35:22 People can raise their hands in the chat. And they can also I see some questions appearing in Halo 21 week six inflows and there was the first person to have his hand up was tough trip and I noticed in the chat I counted.
08:35:35 There's a comment with 15 exclamation points in one line of text. so it looks pretty urgent, Todd.
08:35:43 Very well. Yes, I will bring that slide back so this is from a recent paper by gastronomy, oh sorry I can ask my question first. I'm sorry I mean, you can never have enough exclamation points.
08:36:00 Good. My question actually is seeking clarification.
08:36:05 It may be hard but when you brought in the extra physics, it seemed to change that you know the micro guests physics seems to change the picture substantially So at the beginning of the talk, you mentioned that you know in the cosmos Sims you don't expect
08:36:21 stream feeding except for in the most massive galaxies at redshift zero.
08:36:28 So have you evaluated, whether the, the additional gastro physics changes that to the point where, well, maybe at x equals zero. You could have stream feeding because of these additional complications even for lower mass galaxies.
08:36:46 Right, so that's a great question.
08:36:52 So, these plots that I showed kind of a few times throughout where I've kind of tried to demarcate the different parameters of the streams of the function of Halo nice and redshift you'll notice that I never actually went below redshift one or or be away
08:37:07 from this 1011 to 10 to 14. That was kind of deliberate, I was really focusing here on the more hi Rachel streams, which are feeding you know 10 to the 12 to 10 to 13 solar mass halos it intermediate to high redshift low redshift where we do expect streams
08:37:23 to be feeding very massive clusters. The situation is a little different because we don't actually expect the streams to start out outside the villa radius at cold, Tim the for Kelvin, I'm temperatures the streams themselves are already somewhat more
08:37:41 hot. Turns out that they actually form and accretion shock around them. That was something that I didn't get into here but streams in the intergalactic medium also have had a Christian shocks around them just like you know your dark matter halos have
08:37:55 spherical Christian shocks around them and they expect the low mass halos to be able to cool and form a cold core at their center, whereas the MSA those are likely to be all hot.
08:38:07 The same is true for filaments and once you get to the very massive in terms of their mass per unit length, the very massive filaments which are feeding the most massive clusters at low redshift.
08:38:18 They should be all all kind of hot, so it's no longer a lot of this interesting physics where we talk about the strong cooling do to attend the for Kelvin, etc.
08:38:27 And then the streams being very you know narrow and coherent, sort of breaks down when you get to low redshift very massive clusters, there's still a lot colder than the various temperature of the entire cluster medium so you're talking about, you know,
08:38:40 100,000 to a million Kelvin compared to a 10 plus million Kelvin burial temperature.
08:38:46 But, but some of the details that I've been discussing those would be basically the different regime of the parameter space, which which I haven't studied so explicitly so quite yet but right so so clusters are one thing but what about lower mass halos
08:39:01 it low redshift Do you do expect the same breakdown or could there be still cold streams at low redshift for lower best things. Um, so that's that's a good question.
08:39:16 I would argue, if you're talking about the this situation where you have several separate large intergalactic filaments that are really coming on very large scales from discrete locations to penetrate the Halo is probably not going on, and for example
08:39:32 a milky way mass Halo at Richard zero or lower mass healer, zero because those should be aligned along your, you know, like large scale filaments because the Milky Way is basically at the press Schecter master smaller, what you are very likely to have
08:39:48 is that these individual filaments, you know, could have sub filaments in them or smaller in the star formation community there's sometimes referred to as like fiber bundles or filament bundles.
08:40:00 So I do expect you and have some smaller scale filament theory features that that might be present in lower mash halos it at low redshift but that's not yet really been studied and those are very poorly resolved in cosmological simulations and their properties
08:40:19 might be a little different from the kind of large prominent filaments that I'm describing, but it is a good question, and worth more study.
08:40:27 Okay, so it looks like Mary Putman had a question in the slack which she now believes you have answered, would you expect star formation within cold streams feeding clusters at z of zero, and she after listening to she believes the answer is no.
08:40:44 Is she correct about that that that would be my. If I had to guess I would say yeah I don't expect that likely to happen in fact indie.
08:40:53 So I really only expect this. So if you okay I discussed the concept of students becoming gravitationally unstable. The other thing you have to ask is what is the cooling time in the streams from 10 to the for down to you know 10 or hundred kelvin.
08:41:08 For that you have to make some assumptions about the middle of the city of the streets but turns out that even if the streams are only enriched about 1% silver medalist at the densities at high register so high that above richest for so the cooling time
08:41:22 from 10 to four down to 10 or 100 becomes shorter than the vehicle crossing time, but that breaks down at lower said, so even once you get to ratchet.
08:41:31 Two. I think the densities are such that you that the cooling would be the bottleneck from from 10 before down.
08:41:39 Okay.
08:41:40 Max cranky has a question.
08:41:44 Yes, Thanks a lot near for your for your top.
08:41:48 Thanks a lot near for your for your talk. My I was wondering about, you know, in this cartoon you showed these, these opening angles essentially of the streams, how large are those in reality, and do you think, you know, basically heating or you know
08:42:01 additional terms due to dis compression affects the evolution.
08:42:06 Thanks. No, that's a great question that's actually something that we're studying that we're studying now.
08:42:13 So I don't I don't have a plot here but what we're doing now is actually, together with collaborators at at the CFA and
08:42:24 Jerusalem and yell, we're simulating a cold stream actually trying to penetrate a halo potential where we account for that, you know, as you say the change of the cross section.
08:42:39 I'm analytically, I think it's reasonable to assume that the same mass and treatments scaling should be able to be applied locally at any given Halo centric radius given the cross section of the stream and the density of the the stream there.
08:42:57 What we find when you actually include the halo potential. It kind of slightly messes up descriptions of pressure equilibrium, because the stream is traveling in so super sonically through a steep pressure gradient that if you have kind of if you start
08:43:15 out in pressure equilibrium, then by the time the stream is gotten further in its pressures now much lower compared to its surroundings, but it hasn't had time to react yet because it's traveling so supersonic Lee, and that creates a bit of havoc, and
08:43:29 I don't really know the answer of what the net scaling is going to be but but that is under investigation if that answers your question.
08:43:40 And how large are these opening angles.
08:43:44 Um, well, so if you believe these numbers were the kind of expectation for our stream divided by RV or to be, save ordered 10 or a few 10s of percent.
08:43:57 Whereas,
08:44:00 so that you basically expect the radius of the you so pure central gravity. If the stream is on a purely radio trajectory, then you would almost form a perfect cone, where that this our stream over RV or that like ratio holds at any given Halo centric
08:44:19 radius and practice the streams are not perfect cone, are not a purely like radio orbits they always have some non zero impact parameter. So the scaling is a little you know different but but I would say the first order you can think of this is having
08:44:34 that that same access ratio at any given Halo centric radius so opening angles of a few 10, you know, a few tenths are so
08:44:46 I'm Cameron great talk, great tutorial near, I just had a question you you you mentioned and maybe I missed this
08:44:57 that a lot of the analysis that you you provided here is, is based on these being laminar flows and their initial conditions and, and I know we've been looking at the cosmological simulations and seeing these things flow it, they look laminar, but I'm
08:45:14 wondering if there's been formal analysis on whether on, on how turbulent it is and how the turbulence affects the overall progression of these things once they get into the various.
08:45:25 Yeah, no that's that's I think at this point that's the $64,000 question
08:45:33 it. I would say that the next frontier of studies like this, is to include turbulent, and initial conditions in the ambient medium.
08:45:44 We expect turbulent Mach numbers to be again kind of order Mach one perhaps slightly sub Sonic with respect to the hot Halo. But again, that would imply with compared to the stream itself highly supersonic motions in the background.
08:46:00 And it seems like that must affect the evolution in some in, in some way, either by kind of destroying the, the clean and treatment of coal of additional mass onto the onto the stream or, especially we talk about MMMHD, kind of a very, you know, tangled
08:46:23 turbulent magnetic field is going to behave very differently compared to a laminar magnetic field and in terms of flux freezing and magnetic amplification etc so I agree it's, it's, it's unclear exactly what the net effect of Germans are going to be.
08:46:37 If I had to guess why some cosmological simulations still suggest streams being destroyed in the inner Halo in certain cases.
08:46:50 If I don't just want to blame the resolution and and I think that might be, that's a bit too easy of a solution. I would say that it might be highly turbulent like motions in the inner CGM that that that the stream can't handle.
08:47:06 But, yeah, absolutely. And there's been some interesting work recently by.
08:47:12 I think the first author is Bonanza Barragan trying to study.
08:47:17 What would effectively amount to the cloud crushing problem but not a single cloud but a turbulent cloud complex, and there have been few other results I think the star at all cloud question problem had a turbulent cloud setup and I think there's kind
08:47:31 of slowly moving in the community of redoing all these idealized simulations cloud crushing the stream stability etc and more turbulence initial conditions and I think that's kind of the way we all have to go.
08:47:43 So, so I have a. There's a lot of questions on my mind mice will ask it now, which is of course it's very interesting to understand the idealized problem of a cylindrical flow.
08:47:55 And we know that instabilities develop.
08:47:58 But of course, you know, a filament isn't going to be perfectly cylindrical, as it falls in there going to be pre existing irregularities it could be quite significant.
08:48:10 And, and so the kind of two sides of it is are there reasons to believe that the stream can be self column meeting.
08:48:18 In other words, the conditions of your regular inflow it because you have wakes and such things lead to some self condemnation, more, I could it be that starting with, you know, kind of nonlinear irregularities in the stream begin with could lead to significantly
08:48:39 different results.
08:48:43 Right, well, so it's an interesting question I would say so long as you're simulating the stream kind of in a periodic box.
08:48:54 You could input the initial perturbations as irregularities in the shape of the stream and and that is something that we've experimented with that, in terms of the nonlinear saturation of all the effects, that's equivalent to inducing a linear perturbation
08:49:09 in your like velocity or anything so even if you drastically perturb the shape of the stream some somehow, as long as you assume kind of a periodic flow and you allow infinite time for the instability do a progress that doesn't make any difference when
08:49:23 you have the finite flow within the halo where there's a finite end so you're not looking at how instabilities grow with time, but how they grow with flow with kind of a spatial scale.
08:49:35 There does seem to be more dependence on how you initiate the perturbations and how large you make them because there's only a finite time and again perturbation will grow.
08:49:46 So, I might might yeah I don't have a good answer to how everything would be affected in terms of self colonization, I would think at least when you account for self gravity.
08:50:02 I would. And I think that that to me was, was one of the most remarkable realizations of these streams, is how so many of them are likely to be so close to self gravitating and and in that case I think you'd be hard pressed to severely perturb the shape
08:50:15 of the stream with, you know, without its self correcting itself due to due to gravity, but, But that does remain to be further studied.
08:50:27 Okay.
08:50:28 I'm Nicholas.
08:50:31 I knew I had a question is also a plugin at the same time, the question is, in the Philippines. Sometimes the focus is on the massive Halo is where the filaments Connect but between halos, where you have these, these strings of galaxies as you showed
08:50:46 me one of your first slides, what is the typical mass of galaxies in the filaments on scales of a nickel passing between the massive handles because there's been a recent observation, with the news, extremely deep field at 140 hours on a single deep pointing
08:51:06 of news where people are now starting to see the fuse mission between one and five meters, which might constrain these, these models.
08:51:17 Right.
08:51:19 So, to first order, I would say you kind of expect any like typical halo of order whatever the pressure masses that redshift down toward you know smaller scales.
08:51:32 Of course, a higher order answer would have to take into account clustering and the two point correlation function of different, different masses, that's something that would be very interesting to to do kind of to point correlations statistics along
08:51:49 filaments versus basically not not alone filaments.
08:51:54 So, I don't have the direct answer to that at the moment but I would say, depending on the like redshift I would expect anything of a typical Halo mass typical L star galaxy at that redshift or smaller to define them along the filaments.
08:52:09 These are riches, three, and the galaxies that are in the films tend to have very small now center the 80%. So by redshift three i would say i mean it wouldn't surprise you the most massive Halo you found along there would have a massive 10 to the 11.
08:52:26 Something like that so that might not be too inconsistent with the numbers that you're saying, maybe a little high, but but those would be the most massive ones I would think
08:52:37 there's a question that in the in the slack from Jake Bennett, how like feedback like an agent Shockwave impact the streams as they installed would destroy them.
08:52:46 Yeah, so I mentioned turbulence a few moments ago as being the great unknown yet of this industry I would think that the other great unknown is interaction with strong shocks.
08:53:01 Due to either galactic feedback, or just the stream actually having to pass through the various shock, in the in the first place now interaction with a gn wins etc.
08:53:12 I suppose it depends who you ask. Some would would say, and we've heard a lot about this that you expect the inflows to be kind of alone the major axis in the plan to the disc where'd you expect the strong outflows to be more of a more of a bike conical
08:53:24 shape. So I don't think there would be unanimous agreement about whether or not the winds should actually run into the streams or not.
08:53:34 Certainly plausible that they might in which case it would have to be studied how the interaction of the stream plowing through such a strong shock would would actually work and Jake is long as I was answering your question your great paper, and as I
08:53:49 mentioned on the, on the slack, where you have the trajectories of influence streams through the various shock, I would think would be a very similar question so it might be that streams are going to find kind of low Mark number holes in any kind of shock
08:54:03 shock or wind, and maybe make it through, through there but that should be studied further say next hand up was Avishai.
08:54:16 Just to relate to what Mark was asking network near just said, I want to remind you that the origin of the streams is the cosmic web.
08:54:22 And the shape, and our mail is stopping by some processes that make them into cosmic web on top of the documentary films.
08:54:32 So it's a very interesting question by itself, what happens before they cross the finish organ become and everything that you said about what's happening in the CGM.
08:54:44 We have to first understand what's going on and how to become so narrow and state.
08:54:48 As you saw them in the first writers interview showed, which was a very last term. Freedom 19 big M, which was already narrow and pretty straight pretty significant.
08:55:02 So crystal has both a question in slack and her hand up. I wonder if it's the same one.
08:55:11 Indeed it is.
08:55:14 So I put a picture in slack of one of these head, tail work galaxies, sometimes called commentary.
08:55:23 Galaxies but there's a little dwarf, and there's like a big star forming region on one end and these regions tend to have low gas phase medalist cities compared to the rest of the galaxy.
08:55:35 So it's pretty it's pretty clear it's due to some sort of accretion.
08:55:40 And, you know, perhaps the satellite has been created, but you gotta find the, the evidence for for the interaction right and something has to have dumped you know tend to the seven solar masses of gas and have kind of undetectable stars in it.
08:55:57 If it's a satellite.
08:55:59 So there's been some papers written pointing to these things say you know these are cold streams, hitting dwarf galaxies it Zf zero, these galaxies are very rare, you know, in the in the local universe.
08:56:14 But is this, it sounds like you know from the theoretical expectations.
08:56:20 Cold flows could be completely ruled out for these objects, or if they could be proven for these objects that we can completely derail the theory. So, so how tight Is this okay well I mean I'll say, I guess to at least two things, maybe three, but two
08:56:38 things one the kind of hard limit on the masses that you know have to be like a to sigma peak or to be spoon fed that that's not a hard limit, I mean, in principle, depending on the local environment, especially if you're talking about small galaxies
08:56:53 that are in otherwise voids, there could be local small scale filaments, you know because perhaps like locally that that galaxy is the most massive thing anywhere near it, in which case it would be at the node and be fed by perhaps smaller, more narrow
08:57:09 field and so that that certainly is quite possible.
08:57:13 But the other aspect is and this kind of came up a little bit yesterday in the discussion. I think it.
08:57:21 It's a little hard in our in our discussion to really differentiate the, the thin, like narrow cold streams that are connected, is I wish I said to these intergalactic filaments to just as I think Jonathan will tell us in the next talk, you know, cooling
08:57:38 flows that occur as a result of more isotopic spherical accretion and and then do the slower processes such as you know the cooling and gas being supported by some that angular momentum that they do cool and flow towards the center so I think it's interesting
08:57:57 to try and think about what the telltale signatures of one versus the other would be so that we can see if there's any change in observation Lee and what we infer the main motive accretion to be in the galaxy such as your.
08:58:14 You just showed versus much more massive ones at high redshift, I would think, more in terms of a cooling flow than a cold stream but but that's not to say we can rule out cold streams on 2%.
08:58:27 Okay, well there's been a convenient level and the questioning at two minutes before the hour.
08:58:33 So I think we'll take a five minute break here and have Johnson, start at the three minutes after the hour so those of us who need a break can take it.
08:58:46 And then in discussion following Jonathan's talk will have cooling flow questions but after a while, you know, that we can talk about any mode of accretion so let's all take a break, see three minutes after the hour, and thank you again near that was
08:59:00 excellent. Thank you very much.