08:30:14 And otherwise now starting here, we have Jane Charlton with a tutorial on multi-phase cloudy modeling. So take it away.
08:30:30 Okay.
08:30:43 Okay, perfect.
08:30:45 So, this presentation is something that Samir my graduate student and I put together together. So it's very much a collaborative effort.
08:30:58 And it is very much a tutorial.
08:31:02 It is not a presentation of current thinking or tech, you know, profound technical models. It's really painting a picture of how absorption profiles are shaped and I believe that that is very important to sort of the next step in our ability to pull physical
08:31:22 parameters. Out of these profiles. So here I just show a bunch of different chemical transitions the linemen series lines and metal lines spanning a range of ionization states and the results from some years Bazan cloud by cloud modeling and the contributions
08:31:46 of different phases of Gabs to the different clouds and so we're just going to briefly come back to this later. But the idea here is to explain how these profiles are shaped and how the different physical conditions of the gas, change the appearance of
08:32:06 the profiles. And so I'm just going to present a series of simple simulation models.
08:32:16 But first, What do I mean by the physical properties.
08:32:21 We're going to consider that there are clouds of gas that are shaping the profiles, and each cloud in each phase, has a different number density medalist dr always define that as zero for the solar solar value for logs in the temperature, which is determined
08:32:42 in cloudy. If info ionization equilibrium, but we can have a higher temperature cloud, where conditional processes are dominating the line is shaped by the turbulent the parameter as well as the temperature.
08:33:02 And then of course the abundance pattern which is beyond the scope of what I'm doing here today. And then finally thickness, which can be calculated from the total hydrogen column density, divided by the number density, and I say thickness here, rather
08:33:18 than size because I think it's very important that many of these are nothing close to the spherical structures.
08:33:28 The main insights and so if you already know these things you can you can go out to the breakout room now.
08:33:35 But I'm hoping to illustrate it in a way that might bring up new ideas, the ideas that just shape of these lemons series lines very sensitive to the face structure and they're different contributions to these lines from the different phases, which means
08:33:51 that there's hope of determining medalists cities separately for different phases, even for super imposed clouds.
08:34:00 The second point that I want to make at the end will be that if we're tracing absorbers by a particular ion like magnesium to absorbers carbon for absorbers.
08:34:12 These are not produced by the same types of structures at different read shifts, because of the evolving ABR and so we really need to hold this into account when making interpretations of things like changing covering factors.
08:34:30 This is the first series of models that I wanted to show and these are just idealized simulations.
08:34:39 In this case, I am showing a specific absorption cloud with a column density of 12.5 in magnesium to, you see that there.
08:34:50 The be parameter is of the magnesium two is three kilometers per second.
08:34:56 And I'm showing what happens to the other profiles for clouds of different densities listed here from low to high density which corresponds to high to low ionization parameter.
08:35:14 And you see that carbon for is only here for the lowest density of corresponding to the cloud.
08:35:24 But yet, the iron to his strongest for the higher densities.
08:35:30 And so this sort of shows how the difference additions are used to figure out the density of the structure.
08:35:37 Let me describe a little bit in more detail how we do this, exactly what we're doing is the very simple procedure of using an extra galactic background.
08:35:52 In this case chemistry and on a team for the purpose of this talk, different background radiation shapes and amplitude lead just slightly different results but this is just a broad brush view of things.
08:36:07 And that radiation field, we're going to start it read read just one hears incident not a constant density slab, which has an assumed medalist at a solar abundance pattern assume.
08:36:19 When it is incident on this. It of course affects the organization state of all of the different transitions in these experiments we're always going to be specifying optimize transition, which is going to be a metal line transition.
08:36:33 And so the column does give magnesium to and the parameter of magnesium are going to be specified.
08:36:41 It's best to use a very high resolution data set, to get the optimized transition because that God's how many components, there are, then we're rather cloudy model and cloudy will provide a temperature and column densities for all of the other species.
08:37:03 And then, the temperature, and this is an important point that temperature can be used to figure out from the magnesium profile, what the turbulent the parameter is for that cloud.
08:37:20 Once that is known that turbulent the parameter can be used along with the massive any chemical element.
08:37:30 In this case, hydrogen, to figure out what the bead parameter is of hydrogen.
08:37:39 Knowing that can break some degeneracy he's inferring medalist study with cases where there are saturated lines. So using the metal lines to guide the, the parameter of hydrogen and what that would be.
08:37:58 So this is showing actually something very similar to the first series that I showed with the only difference being the be parameters. This is a little bit broader magnesium to wine.
08:38:10 And it's not making a huge difference to the situation.
08:38:18 In this case though, the, the turbulent is dominating over the thermal be a for the magnesium and the hydrogen lines if we made a comparison would just be a tiny bit broader.
08:38:35 The thicknesses of these four clouds range from 50 parsecs down 2.1 parsecs for the higher density.
08:38:45 These are very, very small.
08:38:50 Here is a plot that I think brings home the idea that we really can constrain metal listening.
08:38:58 At least we can always place a lower limit on what the metal is city has to be, because here we are holding the density fixed and varying the metal is city from minus two, where you see tons of hydrogen necessary to produce the optimized mg to profile,
08:39:23 increasing to minus one, zero and one.
08:39:27 And so what we observe the hydrogen lines to look like is definitely going to be very important in determining the metal listening.
08:39:40 The thickness is very dependent on The Mentalist be with, even for the largest in this case it's 400 parsecs ranging down 2.1 again.
08:39:56 So, the thoughts about the low ionization phase from just looking at these examples, that the degeneracy between the Doppler parameter and. The Mentalist he can be broken using the metal lines to figure out more about how broad these lines really are.
08:40:16 And this is very important.
08:40:21 In cases where we might just have access to lemon alpha and alignment beta in the spectrum can still do something, even with women, alpha and beta and their ways of testing that of course, the low ionization phase tends to contribute to the higher order
08:40:38 alignment series lines, and it also contributes there's a little square bottom of the lineman alpha. That's important for these narrow lines and that's why it does this because these are very small be parameters, typically observed at redshift one values
08:40:55 between say two and eight kilometers per second or common.
08:41:01 Don't get six from photo ionized phases that produce low ionization absorption though of course there are variants on photo ionization equilibrium models that that can perhaps, and then some cloud thicknesses are quite small meaning parsecs scale, meaning
08:41:17 that in most simulations, the cell sizes are bigger than these objects, which means that the low ionization absorption in simulations, is often probing a different kind of structure than the real structures.
08:41:37 So, for low ionization absorption. There are going to be differences, which are going to be subtle and hard to understand.
08:41:49 Now I want to go on to the intermediate ionization phase. So this is a contrast by carbon for, and we're going to set the carbon for column density at 13.5.
08:42:01 And again, very the density, corresponding to these ionization parameters.
08:42:11 The
08:42:14 highest ionization parameter, lowest density that we have here of point oh one per cc is giving rise to oxygen six. So photo ionized oxygen six, we can actually go to a lower density yet, and get a significant amount more of oxygen six in a photo ionized
08:42:39 phase at redshift one.
08:42:41 So that's an important point.
08:42:44 and a difference with redshift zero that we're see. We'll see later.
08:42:49 The lyman alpha profile does depend upon density. In this case, because the more ionized.
08:42:58 We are, the less neutral hydrogen relative to total hydrogen that there is. And we see interesting differences of course in the shapes of these h1 profiles, depending upon the density.
08:43:12 If we make a slightly broader see for cloud.
08:43:17 We see rounder and broader lyman alpha clouds, as well.
08:43:26 And so I just wanted to show that, because we're going to be super imposing these different phases and a little bit.
08:43:34 Now we're going to look at a constant density and a changing metal listening.
08:43:42 So the lower metal listening, showing a lot of hydrogen. Lemon alpha absorption.
08:43:50 But you see how the shapes of these, even for the high metal is the case the super solar metal is the case, the shapes are different than they were for the narrower.
08:44:04 Magnesium to low ionization phase. And so this bit this rounded bit of the profile. We're going to see that that's necessary to explain certain observational data.
08:44:19 The thicknesses of these structures can be significantly larger particularly of course if we have a high ionization parameter, but they can also for very high medalists at the very small.
08:44:36 And so there's a whole range of things out there, producing potentially carbon for absorption as well in this intermediate organization fit.
08:44:50 So, in this case, in some cases for some densities, you can get low ionization and oxygen six absorption at redshift one.
08:45:02 These are often broader clouds, and that changes the way that they contribute to the lyman series and Lama and alpha lines.
08:45:12 The typical neutral column density. For these are smaller than the low ionization phase, but their contribution to lemon alpha can be very important, and even dominant due to their larger be parameter.
08:45:28 And then the cloud thicknesses can cover a large range but they're typically larger than low ionization phase clouds.
08:45:38 Now I want to look briefly at oxygen six, and this is going to be a collision away ionized model, where the oxygen six has a column density of 13.5 so relatively weak and the temperature, changing, 5.3 5.35 5.5 and 5.7 we start to see the neon eight just
08:46:03 barely at 5.7.
08:46:09 And we see carbon for at the lower temperature. So there can be carbon, or from a collision Li ionized says as well.
08:46:18 These can be broader and notice the hydrogen, that there is a broad profile, and for certain lower temperatures. We see interesting wings here that are going to be important for explaining some observational profiles that it seems really cannot be explained
08:46:41 in any other way.
08:46:45 Here is the example of looking at the metal listening for a fixed temperature.
08:46:53 And we see that the medalist he does not affect the ratios of the metal lines at all.
08:47:02 As it shouldn't.
08:47:04 And we see that the metal issue it is a very important diagnostic of how strong or I should say the other way around. The wings are going to be a very strong diagnostic of what the metal is the have such a collision only ionized phase would be relying
08:47:22 on a temperature that can be determined by constraints from the metal ones.
08:47:28 So the thoughts here depending upon the temperature, these different species can arise
08:47:40 from occasionally ionized phase, the typical nh one is really quite small, but it can be very broad, the density can't be measured but it's likely to be small and, if so, there are six feel most likely.
08:48:04 this phase, this is the same thing that Todd said yesterday. It's easy to do. It's about 10 times higher temperature than lower intermediate ionization phases.
08:48:12 And so the density would need to be about a factor of 10 lower.
08:48:18 Let's put these phases together. Let's do a three cloud model where they're all three clouds centered at the same velocity.
08:48:27 And so the low ionization phase, you see here in magnesium to the gold is the carbon for intermediate ization phase. And then there is an oxygen six phase that we see in green.
08:48:45 And we see how nicely. These fit together to shape a lineman alpha profile which is shown in the dotted line here.
08:48:58 So for the low ionization phase.
08:49:05 The medalist he is fairly clearly going to be constrained by anything we see in Lyman beta and below but even also by this little square region at the bottom of the lyman alpha profile, one really does see this and observational data.
08:49:21 The carbon for is going to be constrained by this region of the woman alpha profile.
08:49:30 Right, so that's a little bit subtle, but also you need something to explain this.
08:49:37 It doesn't do it for the bottom notch but it will do it here. And certainly, you can place a limit on it because for any lower medalist at, it would exceed the observed profile substantially.
08:49:51 The oxygen six when it exists produces these wings, which also are sometimes observed and so that can also be constrained and then metal is it can be constrained
08:50:08 the sizes of these clouds. Four kilowatt hours for parsecs 164 six. And then, we're not sure about the six exactly without knowing the density.
08:50:23 Hey, let's add in another cloud.
08:50:27 This time, it's another see for cloud we often see these that's offset by 15, kilometers per second.
08:50:34 So these carbon four clouds are blending together and producing an asymmetric profile in the lime and alpha again something that we often see as well as in these spaces.
08:50:46 So the important point here is that we can constrain the metal liberties. For each of these by using little tricks in certain portions of the profiles, right for the low ionization.
08:51:03 It's the series lines.
08:51:05 In this case, the square bottom isn't really doing it for us but it certainly would for Lyman beta.
08:51:13 In the case of the carbon for on the left, that one can be constrained by this left side of the lemon alpha.
08:51:22 The carbon for on the right is clearly constrained by this region on the right, and then the oxygen six by these waves.
08:51:35 So it really is possible to separate these profiles into different phases, and several groups are working on this, on looking at variations of metal the city across the system.
08:51:50 There was some pioneering work in 2019.
08:51:55 Many people had done it more by hand.
08:51:58 For the last two decades really but but now it's possible to do you know a more rigorous Basie and cloud like cloud modeling and infer medalist cities and densities with error bars.
08:52:15 Samir my grad student has one of these new methods and his really relies on the shapes of the profiles compares simulated profiles from fidelity to the data and then optimizes what the parameters are in the different phases.
08:52:37 And so, here are some quick results from his paper but I direct you to his four minute presentation on the YouTube channel or his paper in Monthly Notices that's already available there that you can see the variation in metal listening of different clouds
08:52:59 across these four different absorbers and how much more there is to see with metal is the compared to averages, that can be determined just by a single column density.
08:53:13 So the final point is, how does how did these structures evolve and how did the absorption line profiles, get affected by that. So a simple thought experiment here to do is let's take the redshift one example that I gave example to.
08:53:33 and let's fix the density.
08:53:35 So the same as in the redshift one case, the metal listening.
08:53:41 The nh total in the be turbulent for each of the components. So let's try to take a physical structure that existed at redshift one.
08:53:53 And let's plop that same structure down at redshift zero, where there's a different extra galactic background radiation, really simple nothing too terribly profound.
08:54:07 Let's keep the ionized phase, the same node, having the same density and temperature, like as if galaxies were behaving the same way and the same processes were producing structures.
08:54:18 But let's see what the absorption system would look like.
08:54:22 So here was the case that I showed you a little bit ago at redshift one.
08:54:27 Notice the offset see for cloud.
08:54:30 The single component in magnesium, two, and the oxygen six with a little bit of a contribution from the sea for photo ionized phase evolve to redshift zero.
08:54:49 We're not seeing
08:54:52 the same situation at all.
08:54:56 We are seeing a situation where the magnesium, two is stronger, and would be detected in the offset see for cloud.
08:55:07 So, this cloud was alone in the sea for cloud, then this would be a
08:55:17 magnesium to cloud at low retrofit it would have a lower density than those then higher redshift so the whole population of low ionization absorbers at low redshift are on average lower density, especially the week once
08:55:35 we see that the photo ionized oxygen six which could have been considerably stronger if we had gone with a lower density is absent at low redshift.
08:55:47 And we see that at redshift one we could have a situation where we had more photo ionized guess where that would completely dominate this collision line ization.
08:55:59 Okay.
08:56:02 So, I know you're just wrapping up now, I want to do a time for for a little bit of a break so I know this is your last slide so immediately after this slide, you know, people can join the breakout room and you can finish this discussion, and yeah we'll
08:56:21 start the other tutorial right at 9am.
08:56:25 Okay, let me just finish up here. So what I wanted to say is that there can be hot gas and halos at low redshift, and why wouldn't there also be at higher redshift that it might be hidden below a photo ionized phase.
08:56:43 And so, because of this change. When we think of like Halo covering factors for gas we should think of Yes, of a certain density, not guess praised by a certain chemical species.
08:56:57 So I'll just put up my closing thoughts, and people can take their break if I'm allowed to share for just a tad longer. Yes you are. And actually, you're allowed to share this in your breakout room which might be a good way to kind of transition to the
08:57:12 discussion that follows this thank you so much for that masterclass and cloudy modeling that's really great. As someone who's done it, but kind of in bulk it's some really interesting stuff.
08:57:25 Okay, so we're going to take a little bit of a break now to give everybody a chance to, you know, do what they need to do.
08:57:32 And, and so there is a breakout room that you can join already and actually I think a few people have already joined it. It's called cloudy tutorial creatively, so you can.
08:57:47 I think that there are a few ways to join these open breakout rooms, but if you have the breakout room button on the bottom of your screen that's the easiest way all of these rooms are open, unable to join.
08:58:01 So, if you want to participate in the cloudy discussion I highly encourage you to head over there. If for some reason your zoom isn't like up to date.
08:58:10 You can DM me, and I'll try to send you directly there I can actually move you physically if you need me to do that.
08:58:20 I'm happy to.
08:58:22 And yeah, I will see you will see back and just a couple minutes now for a Shmuel's tutorial.
08:58:30 Thanks everyone.