09:06:01 Okay everybody, it's 906. Welcome back. I see our expert panelists here.
09:06:12 In particular, Evan Schneider. I haven't if you want to wave, go ahead and wave, seven, eight.
09:06:20 And then we have Jonathan start who actually just stepped away from his computer so he can't wave right now.
09:06:27 And Max grumpy if you want to wave IMAX and and critique Sharma.
09:06:38 Here I'm particular yes hi critique thanks for waving.
09:06:40 There's Jonathan Jonathan if you want to weigh your for people so they know you're one of our expert panelists. All right, well, if everyday, that's Jonathan doesn't have his headphones in yet putting his headphones in hi Jonathan.
09:06:52 Welcome back to the expert panel discussion okay so there's a ton of really interesting questions and comments from the slack. Based on what was being widely hailed as a tour de force classic presentation.
09:07:09 Thanks drum and that's exactly the kind of keynote we were hoping for. And in particular, what I really liked, is that it juxtaposed, so I thought, Todd did an excellent job on Tuesday, have really, you know, giving us an idea of how rich, the data, we
09:07:38 are, but also that they are limited to some degree, as well in terms of what we can glean from them, and then you went ahead and showed us all of these beautiful predictions that really tell us, of this interdependence of the different physical skills
09:07:40 and processes happening.
09:07:43 That can distinguish, you know, between the different phases that emerged in the CGM and so I guess the first question I think would be a really interesting one for the the panelists to address would just be, you know what, what are the properties that
09:08:13 you most need one of the things that I noticed looks like cloud sizes or stream thicknesses, or masses or densities or medalist cities or pressures what what are the like most important constraints that observers should really focus on on pinning down.
09:08:17 Yeah. Excellent, excellent question since I just talked so much I do any of the panelists immediately want to jump in and chime in on that.
09:08:29 Um, okay well I'll start you know I kind of wanted to show that, that little candy stripe visualization at the end there as, as, you know, as a hint towards what we might need you know I do think it's very challenging because, as you saw a lot of these
09:08:48 timescales were indeed relative to a cloud size which is probably not something we're going to be able to measure so well that's the if we can get a robust observational probe of an individual closet cloud size that would be, you know, amazing but you
09:09:08 know I think we can learn a lot about the face structure and
09:09:14 yeah the interconnectedness of the different phases in the clouds and the dominant processes by really looking at you know the the line ratios and resolving the different lines like we were seeing in that multi-phase movie there at the end.
09:09:29 Yeah, so I don't know I'm a little brain dead from all that talking so so someone else I'll think of more things to that as we go okay see Evans unmuted.
09:09:39 Yeah, yeah. I was gonna say I could I could add something I think maybe just because I agree that cloud sizes are important, obviously that was part of the reason I derailed Tuesday with my question about what what observers even mean when they say a
09:09:53 mist versus a cloud.
09:09:56 But I think something maybe we could get a handle on that is important to this whole discussion is sort of the actual spatial correlation of these different phases.
09:10:08 So, you know Drummond's swipe this as I'm sure it will be known forever does a really nice job highlighting that, at least for some of these multi phase models, you know the accident six should be very spatially correlated with these lower ions, and I
09:10:35 even in you know some of the some of the absorption line data some of the really nice data for example that Glenn was showing it seems like observers are starting to get a handle on on that. And I think that not all of the sources of multi phase gas that
09:10:39 drumming outlined will be as spatially correlated, as that. So I think that's one area where, where it would be really helpful in distinguishing between some of these different models and some of these different sources of multi-phase gas.
09:10:56 I see Christmas he has his hand up Chris if you want to unmute.
09:11:00 Sure, I can you hear me. Yes. Yeah.
09:11:03 So I wanted to ask
09:11:07 you just muted muted you I meant to lower your hand, I muted you Chris, if you want to unmute yourself now I can't unmute you.
09:11:16 Okay, so I want you to know. Yeah. Yeah. Thank you.
09:11:22 This. Maybe this is I said a question for the observers to try to get to the point the drama was making about cloud sighs, What are the prospects, particularly with the upcoming LTS to actually be able to get absorption line spatially results for approx
09:11:38 approximate observations that is, instead of using a quasar which is a point so I should actually use a distributed source and do, will there be the sensitivity of resolution, to be able to do that with future instruments.
09:11:52 We have our other keynote speaker with his hand. Raise Todd track who has possibly thought about this question that you pose.
09:12:00 I just want to remind everyone about the excellent paper that Michael Roque wrote many years ago, looking at gravitationally lens quasars or just adjacent quasars which placed some very interesting constraints on the sizes of the absorbers.
09:12:17 And I think with future large telescopes that kind of experiment, could be revisited with larger samples and and maybe even other species.
09:12:30 I think Michael just looked at. Well, he looked at carbon four and H one I don't remember if there was a magnesium to paper, but that's a promising way with big ground based telescopes to get some information on sizes.
09:12:47 Also, following up on Chris's question I just want to add one thing there is some, some very nice work by Kate Rubin using background galaxies as the absorption source to sort of be able to constrain the size of the absorber because the background galaxy
09:13:03 is no longer a point sources resolved. and you could imagine.
09:13:08 You know, that taking to the nth degree with with even more powerful telescopes and really actually like looking at how absorption changes across the face of the galaxy that might be an incredibly powerful way going forward, to really get at Chris's question
09:13:24 of the spatial structure in the in the cloud size of. Yeah, of these systems.
09:13:31 Okay, I see we have a lot of hands up, I'm going to ask. Okay, what I'm going to do is I'm Glenn had her hand up before so I'll ask when to say something and then I would just I want to get a chance to all of the panelists to kind of, you know, give,
09:13:44 give their view their expert view and then we'll go back to the kind of hand raising stuff.
09:13:51 Okay so Glenn, go ahead.
09:13:54 Yeah, so I just wanted to comment on this idea of using the ELT us to map the CGM and sort of a special resolved way.
09:14:02 So, as was just mentioned if you use something like a gravitational lens background galaxy, you can actually sort of have a light table type situation, and then your resolution is basically limited by the the resolution of the battlefield unit that you're
09:14:16 using the spatial resolution.
09:14:19 I think in some sense, our, our best hope is still going to be quasars just because the size scale that they probe is limited by the actual, you know that the light from the the quasar itself which is small on at the location of these absorbers, whereas
09:14:34 background galaxies are always extended Of course, and, and because of that if the size scale of the clouds are much smaller than the projected size of the galaxy at that redshift which will essentially always be the case that appears.
09:14:50 Then what you actually measure is the covering fraction of this gas, as opposed to directly measuring, it's sort of size scale. And so I still think actually looking at larger samples of lens quasars might actually be the path to this.
09:15:04 There's also been beautiful work doing very very careful photo ionization analysis to try and get a cloud sizes, and we're at the point now when we do this sort of component by component analysis where you see similar answers coming from that as you see
09:15:15 from lens work like Michael routes work has been pointed out, and, and then a paper that I published last year also showed a similar example in the CGM specifically.
09:15:25 And so I think, you know, I agree that the sizes are really critical and it's something that I think we really need to be paying close attention to in terms of trying to do any sort of comparison between simulations and observations.
09:15:36 But I think in terms like you know I'm super excited about doing these spatially resolved CGM maps using background galaxies. This is one of the main science cases for the ELT but it's not I don't think it's going to be crazy useful for measuring sizes,
09:15:47 I think it's going to be much more useful for looking at the spatial correlation across the halo of structures and seeing whether whether you see large dramatic patterns in in that structure.
09:15:59 Okay, that's my guess. Thanks Glenn.
09:16:02 Okay, I want to give each of the panelists time to kind of process some of this on this subject or maybe they want to veer on to another subject that really inspired them from Drummond slides.
09:16:12 And I also just want to point out that some of these questions about sizes can be answered by looking at the Milky Way and being able to do kind of Halo tomography.
09:16:22 And so that's coming up week four and I'm sure we'll hear more about that then to to plug week four okay so panelists who have the panel, it looks like batik has his hand up he's on the panel so you might as well go ahead and I just wanted to add to this
09:16:37 that I heard the talk by Celine pillow in.
09:16:44 So, and she was actually talking about extended galaxies mapping the foreground CGM so it's similar to what Don mentioned. So, looks like, and also other speakers, I just wanted to add that because I had heard,
09:17:01 I think. Yeah.
09:17:03 Thank you.
09:17:05 All right. Well, uh, let's see, Max.
09:17:09 Yeah, I my first of all I want to thank Grover for Austin talk always Rockstar like of course and then and that conference relations I mean that's amazing use your shirt with all of us, but for the science I mean I also wanted to mention Sally's work
09:17:23 and also Sebastian Lopez who does this uses length background arcs, I think that's very, very nice. Or, but I think, and I think Joe pointed this out you know and Slack channel.
09:17:35 I mean it's pretty clear right that the size is small, I mean, you know, the question is just how small and I mean, seems to crystallize out and that it's, it's probably smaller than than what we can can do directly in observations except maybe not always
09:17:50 I'm very excited about that week as well. And I just want to bring up one point that you know came up in the the slack discussion in the past few days, and has to do with that that is that we have to be careful to correlate like sizes and sizes in velocity
09:18:07 space right if you look at, Kate Rubens for instance that was mentioned before, that's where size of in velocity space so to speak right and and.
09:18:17 And so the question is, you know, is, is because what what drama showed essentially right is that you know there there's these observations that show stuff it's very small, but then you know in order to make gas survive, you or, you know, did it has to
09:18:31 be somewhat large.
09:18:33 So I think that that's some kind of interesting discrepancy and I mean it maybe somebody can say something about it.
09:18:45 Jonathan. Do you want to add to that.
09:18:48 Yet, two quick points, can you hear me.
09:18:51 One thing which I think is super useful it's kind of gaining speed in the last few years is kind of mapping loud skill structure of the CGM, so kind of understanding is the cool gas in the displaying, is it a longer mind relaxes a.
09:19:19 I think these kinds of observations which we kind of need lots of statistics, all these a next generation of absorbers is very valid because once you know the location of the cool gas, right that already kind of knows downs, which mechanisms could create
09:19:39 it, so it tells you a lot about that. If you know that the cool yes is not volume feeling like in a couple of like showing that there's a by modal distribution of gas as a function of anger from the mind relaxes.
09:19:52 That also kind of narrows down switch mechanisms because that tells you that whatever mechanism is trading cool guess it's not happening in the entire Halo it's only happening at some specific places in the handle.
09:20:03 So I think those kinds of observations which are becoming more and more available are becoming a very will be very useful into an can have to understand where we are in the School of fortune that a TV show.
09:20:16 And that's one thing, one more kind of to add one more thing, a cause of crude gas is location. Okay, when the hot gas, when you go small scale the hot gas is expected to actually locate.
09:20:29 That's another mechanism, which would create a cool yes and that's there's a few very interesting studies about that. And just to make the picture even a bit more complicated.
09:20:41 Yeah, so just wanted to mention that.
09:20:45 Great, and and something that I just saw come up on the slide but maybe somebody wants to weigh on maybe, maybe Evan, even as the person to weigh in on this but, um, so crystal asked and I think that this really gets to the the crux of it.
09:21:00 So, how is size, even defined for one of the simulation like those kinds of simulations that we're seeing right there's little clouds with a distribution of sizes and they're organized into larger scale coherent structures right so so how, how do you
09:21:13 actually on a simulation say now you have all the data on the simulation, what, how do you define it so Evan, I'm going to let you go, since you're on the panel, and then I'll take some hands.
09:21:23 Thanks. Yeah, no, I would love to weigh in on this because I think this is a question that we, I think we've gotten a little bit. I don't want to say distracted because I think these questions are theoretically very interesting but little bit distracted
09:21:34 by the sort of minimum size of the cloud that we think should exist, but something that has struck me, at least in the vast majority of the theoretical work I've looked at you can look at for example, you know, the potato cloud, you know shattering versus
09:21:51 not shattering case from Max's paper that drumming showed is that even in the case where you shatter and you have many, many tiny, tiny little, little clouds, there's always large scale clouds as well.
09:22:02 And so it's not clear to me from the observations that those two cases would look any different, right, especially if all you have is an absorption line.
09:22:11 And so, so I think that this is an important question for us to sort of address, theoretically is, you know, we kind of, I think, agree that in our simulations, we're, we're almost always getting some structure down to the resolution scale of the simulation,
09:22:28 but is that the structure that matters. And we talked about this a little bit in one of the, one of the channels and I've already forgotten which one but but drumming alluded to it and his talk to where it's sort of like well I think it depends on the
09:22:40 question that you're trying to answer the question you're trying to answer is you know how much cool gas is there in the CGM, maybe don't really care if some of it is in tiny clouds if that's not, you know, the picture that we should have in our heads.
09:22:54 And so far from theory I haven't seen any simulations that indicates to me that the picture I should have is an actual, you know, volume feeling missed.
09:23:05 I almost always see these larger scale structures.
09:23:10 So I think I think that is an important point to think about and whether or not, observational, we would be able to distinguish between those two cases.
09:23:18 And that's that gets me thinking too. It's like, so what do you what you said what's the question that we're trying to answer right from for me I think about where did the guys come from and where is it going.
09:23:30 Right. And so this gets to something that Joe when said, is just like, Is there a way with some of these parameters that we can determine cloud sizes masses to actually distinguish between the different origin scenarios or and or fate scenarios.
09:23:47 Okay, so unless, and so okay maybe that maybe that just gets tangled I said I would go to questions. I've seen near with his hand up for a while.
09:23:59 Thanks. Thanks very much. And also thanks to Drummond again for a great talk and congratulations on the wonderful news.
09:24:06 This might be kind of slightly a separate issue but we've talked a lot about the formation of the multi-phase gas kind of down to tend to the four. What do people think about the molecular gas content of the CGM.
09:24:21 Are those Is it at all possible to form that due to NC to thermal condensation or instabilities or do those are does molecular gas necessarily originate in either an inflow and outflow or RAM pressure stripped you know galaxy do we think it can form an
09:24:37 inflows.
09:24:40 Yeah.
09:24:45 panelists.
09:24:43 I can. Yeah, so I think, in principle, if you're dense enough to self heal from the movie backgrounds. Right then, you can include the very low temperatures and then create more liquid or gas.
09:24:53 So I think that the density is relatively low at low which if so it's unlikely, but perhaps if you go to a higher chance that through that you have three or four, then see how much loud you said cheating becomes much more important than it seems reasonable
09:25:07 that maybe you even reach the point that you get two molecules
09:25:15 from thermal condensation in the hot CGM or you're talking about an influence streams or, or, or both.
09:25:22 If you manage to extend to the 4k, whatever pulses you choose yeah okay and then but you'll dense enough to be self shielded, then you will further cool.
09:25:31 So I guess the question is do we expect precipitated clouds, to be able to become dense enough to self shield.
09:25:39 Yes, that's expected that at higher densities are generally higher.
09:25:48 Well I don't know because of the densities are higher their sizes will be smaller, presumably given the cooling length argument.
09:25:55 Right, so do we expect them to have a column density that would allow them to self shield.
09:26:03 Yes, so exactly what you care about is kind of what's the characteristic Columban right so the density is increasing as one to 1% to the third, and the sizes right only decrease you guys want to the one place that to the minus one.
09:26:19 Right. So, in column, the columns in the CGM are much larger that higher rich. Right, okay.
09:26:28 Right. I said I was going to go to hands right sorry really really quickly Mark added a great point you most likely need dust to form molecules. And so I know Max and Ryan Farber are working on the cloud crushing problem with dust and seeing how it can
09:26:46 survive. So, if you're just if you've just got sort of like a dust free hot CGM with some perturbations, and it's collapsing, even if it's self shields.
09:26:59 I don't know if you're going to form molecules. So that's you know that's that's a, you know, an additional point to consider.
09:27:04 Thank you. Yes, dust is the main way that molecules for him in the first place so it's good to remember that.
09:27:11 Okay, so I have lost track of the time I think my son Marcus his hand, a long time ago so marketing to add something here Well, maybe you just want to make two points.
09:27:25 Start was writing on the slack as well. I liked.
09:27:39 Romans Wheel of Fortune chart, and I think there's a bit of analogies, just like with equilibrium dynamics cooling is trying to pull the guys away to a new point of equilibrium, and all the other points Kevin Hamels mixing free for wherever you want to
09:27:44 try to counteract this, and this, this may be two points one could make one, one of these other competing processes is thermal conduction. And sometimes, thermal conduction doesn't actually work the way it is.
09:27:59 You think silver production would act against it but I've shown in simulations with Emmons gonna pay for that conduction actually, because it cause causes evaporated winds of the surface of these clouds, makes it really actually compresses the cold clouds
09:28:20 and makes them actually cool faster so sometimes things are a little unexpected in with these competing processes. That's, that's not easy. So the other thing that can complicate things if you got another face in there like awesome laser magnetic fields
09:28:29 that talk to the gas, and they've got different state variables and different dynamics and different equilibrium, that they like to seek.
09:28:37 And if they communicate with the gas then you know all, you will have the rough, anything can happen then and and some simulations have shown this that if you've got other phases talking to the thermal gas things become much more complicated.
09:28:54 Maybe it's the bleeding obvious but anyway, this is cast.
09:29:15 And those are those are really excellent points. Thank you, Marcus I you know the equilibrium dynamics is definitely a useful way to think about this and as far as conduction goes I'll just say for my for my, my own sake you know Chris McKee who I'm happy
09:29:08 to see is on the line was the first person I worked with in graduate school. The first paper I wrote was with Chris. And so I feel like I was, I was raised on, on, on some of this stuff in a sense you know, like lately, in particular, Greg Brian and I
09:29:27 have been looking over Cali and Mickey and Kelly 1977 78 to really, you know, understand exactly these points you're saying conductive evaporation conductive condensation and really trying to fold this into our understanding, I would say that, at least
09:29:47 from the turbulent mixing layer perspective, I would say, yeah, Mark just said props to Chris Mickey in the chat. I mean, yeah, exactly I keep on thinking I discovered something and then it turns out Chris wrote a paper on it 50 years ago.
09:30:03 But, Yes, yes i think i think that's a statement of being a good beer so that's that.
09:30:15 But the point I'm just going to say about the turbulent mixing with conduction included is if this sort of effective turbulent conductivity swamps, the actual thermal conductivity, then the, the overall evolution doesn't seem to look that different based
09:30:36 on experiments I've done in work that Brent can published last year. And once they start to become comfortable i think that's that's a really important question and as you say, you know, add magnetic fields or non thermal pressure, and it just gets just
09:30:52 gets more more exciting, so I'm sure some of the other panelists probably want to add.
09:31:00 Yeah, it looks like critique your panelists, you don't have to raise your hand critique as a panelist, right. So, I had no I had a comment about molecular gas in galaxy clusters goals of galaxy classes, most of the mass is in the molecular phase and not
09:31:21 in the Atomic Age alpha phase. And I think one of the very important reason for that is also the pressure, if you look at the two phase models, you know there again, Chris is another pioneers modifier at all type models, you know, the pressure plays a
09:31:37 very important role in determining which phase.
09:31:41 Does the cooler, you know, do you have two phases coexisting or is it the dense molecular phase of the less dense atomic Phase I think pressure in addition to dust and self healing, these are, you know, these are all very very important and pest pressure
09:31:58 i think is, you know, like galactic high velocity clouds do not really show evidence for Molecular gas genuinely, but cluster filaments are very molecular so and and the big difference between clusters and military Halo is the pressure I think that that's
09:32:18 an excellent point I just outside very quickly I just started a thread in the Slack channel because this is something that Greg and smell, and I have been talking about exactly this point pressure, pressure being key sorry I've been Go for it.
09:32:31 Oh no, I was just going to use panelists privilege and tag on to that that this is related to a question that I saw in the slack that I get a lot about whether or not these cooled clouds are going to become self gravitating because people want to know
09:32:44 about star formation. It mean, it depends. 100% on the pressure on whether or not you can actually cool down to the molecular face so in the average, you know Milky Way Halo know you're not going to precipitate out cool clouds that are going to become
09:32:58 No, you're not going to precipitate out cool clouds that are going to become self gravitating, but in in more, you know, in higher pressure environments, I don't know.
09:33:07 Excellent calling Stephanie Thomason who's been thinking about this in the sci fi in the entire cluster medium in that simulation I showed, so I don't, she doesn't necessarily respond now but good person to talk to about that if you're interested.
09:33:23 Okay, I want to get to something on the Slack channel, but I've seen you on lead with her hand up for a while so I'm going to ask you want to ask.
09:33:35 Yeah, I think I had a question earlier but now I want to follow up on what Mark mentioned about dust, and mostly I guess my question is for the observers.
09:33:47 I really don't know if we've observed Dustin the CGM either in the quarter face or de warmer phase hotter phase whatever you call that. So what what's the current status on observations of dust in the CGM.
09:34:02 There was a really cool result back in. Gosh, I don't remember the year anymore but Bruce Menard, and he blogs and they found this like really cool like dust correlation in the CGM and I've always thought about that, like they see dust out to 50 kilowatts
09:34:21 parsecs it's a stalking experiment with SPSS data and using like extinction. And it's amazing, and so I will point out to my own result of far as Dustin a CGM in the Milky Way, we think, probably the ionized gas can also be dusty Chris help did work on
09:34:38 on this that in the whim at least the warm eyes medium that's kind of puffy maybe that there's probably some dust there too, there's evidence at least that there's significant amounts of dust there I don't know about others.
09:34:54 There's been a lot more progress on the halo calls into question the result by Menard.
09:35:01 And it was by Johnson I think within a year or two after that.
09:35:10 And
09:35:10 Hodges cluck has seen just scattering UV scattering by just as a function of height above edge on galaxies.
09:35:21 And so one can see that the creases and actually may change the dust type may change about twiddle 5468. Thank you.
09:35:36 Okay, so there, there's one thing I want to get you on the slack I see you all with your hands up I will come back to you if there's time.
09:35:43 But I do want to give some priority to the slack which I have strongly encouraged using. And so one I think very interesting comment that's gotten some discussion and replies, is by Frank Vanden Bosch, and he said, You know he loves the Wheel of Fortune
09:35:58 but he thinks the really hard question is how to heat, cold gas, and in particular, how can we trust simulations of the dominant heating mechanism, other than a diabetic compression is not treated properly so if any of the panelists want to talk a little
09:36:14 bit about heating.
09:36:17 That would be.
09:36:19 I think useful.
09:36:37 More specifically Renzo this cosmic ray heating is radiative heating, but often has not included except for maybe you'll be background and drama you showed at some point this idea where you had this outflow and you had some cold gas in it, and then you
09:36:45 show that the little young to kill a plastic or something you argue that's on that cool guys being transferred back into the hot face.
09:36:46 And you link that sort of a launch kill turbulence of the material, and I'm trying to understand what you're trying to imply that I have the impression of what you're trying to say is that you know the logical turbulence sort of stretches it out, Greece's
09:37:06 that area of the surface layer, and I will promote conduction, because that's basically the only heating that's in that simulation I suppose so. Yeah, no, yeah, I'm wondering about the new metrics and then what do we actually, you know, are we fooling
09:37:11 ourselves. this is all numerical rather than physical.
09:37:14 Yeah, so. Okay, so, you know, we, of course, are doing all of this numerically, as you say, and you have a cold phase it's got a contact discontinuity with the hot phase and then you've got some turbulence and that turbulence is going to mix up that contact
09:37:31 discontinuity until the effective surface area gets so large that the conductive time no matter what the actual conduction is becomes fast.
09:37:40 Right, so this is as as Brent tan put in his paper. This is why milk mixes into coffee, even though the molecular diffusion time is of order the age of the universe, but you stir it with a spoon and it builds up a surface area that so large that you back
09:37:57 Eventually, mix and as you say, heat the gas you know conducted the heat the gas. So, you know, I think there is definitely a lot to be questioned about our simulations and the fact that we're not resolving the fields blank which is really what you would
09:38:13 need to do to properly to properly do this. I think both Brent and I have turbulent mixing layers simulations brands are really nicely published in their recent turbulent combustion analogy paper, where they were they show that even resolving the field
09:38:31 winning. You know you.
09:38:34 You get this mixing in this meeting and so the point I was trying to make about Evans.
09:38:38 Beautiful simulation with a turbulent background in the hot phase is it's doing exactly that, as you said, it's stretching out the clouds it's splitting them into smaller and smaller parts, until you know their surface area gets so large that in the case
09:38:59 of her simulations and I would say, essentially, 99% of our simulations, we reach the sort of the disability scale of our simulation the grid scale where they're numerically mixed, even if we had infinite resolution and some small degree of thermal conduction,
09:39:09 I think the same process would happen.
09:39:13 That's my that's my personal perspective, I think, you know, there's about 1000 people in this chat who could who could add.
09:39:25 I think that's a great perspective. Okay, I'm going to go back to the hands.
09:39:31 And I've seen Todd with his hand up for a while so Todd, go ahead. Thank you very much, so I really liked the drift skin thing at the end, drove into the have a question related to that so it's a sort of a two part question.
09:39:46 So the first part is that we we use metals to try to get more information.
09:39:53 There's just a lot of information there but we have to have some kind of ionization correction, often.
09:40:00 Um, so we shouldn't code like cloudy, which students total balance and ionization equilibrium.
09:40:06 But the densities are expected to be low. So have folks looked at whether or not the timescales are indicating that that ionization code is even valid do mean do we expect those equilibrium.
09:40:32 Oh, Todd.
09:40:34 Yeah, I think, I think we're losing the tide.
09:40:39 Anyway,
09:40:41 Todd is now frozen. So, all right let me.
09:40:45 I think I think I got the the gist of it so let me try to start the answer to this and I'd really encourage help from everyone.
09:40:54 You know I think this relates back to a question Greg asked about Todd's discussion on Tuesday where Todd showed some oxygen six absorption.
09:41:07 That was incredibly narrow that pointed to very very cold oxygen six, and he hypothesized that this might be sort of over ionized auction six something that auction six that has cooled so rapidly that its ionization hasn't been able to keep up and I think
09:41:25 that's a very compelling idea to explain those sorts of observations Greg asked this question in particular, asking how common that is and I don't think that question got picked up so I'd like to just re highlight it because I'd love to know how common.
09:41:41 That is because it bears on this question taught us now. I think some of the time, basically. Wait, so I'm sorry I actually lost my connection and miss the juicy answer I was looking for.
09:41:54 So as far as how common those narrow oxygen six absorbers Are we really don't know because it's a super hard and expensive observation.
09:42:04 I think I might have looked at the one Quasar that's bright enough to do in an amount of time that a panel would go for so that might be a question for future space telescopes but, and I'm continuing to think about it.
09:42:18 Yeah, so I'll just very briefly say searching g looked at turbulent radiative mixing layers like I looked at with non equilibrium cooling and ionization states there I think they didn't quite probe the rapid cooling enough regimes, where you would get
09:42:38 some of this out of equilibrium, you know, over ionization of the auction six but I think it's a, you know, the timescales aren't, especially for oxygen six aren't that different between ionization equilibrium in the cooling time.
09:42:52 So, I'm sure a bunch of people need to correct me on things I said wrong.
09:42:59 Thanks.
09:43:16 Thanks, awesome God government. So my question is, it's rather a comment so I really liked your wheel of fortune. So, yeah, in the, in the wheel of fortune for all the different physical setups, you present a different criteria is based on the cooling
09:43:35 time.
09:43:36 and the flow time to be very specific the flow time So, can we generalize all these criteria based on the damn cooler number presented in present tense paper.
09:43:49 As your simulations are nothing but hydropower schooling setups. So the reaction time skill is nothing but the cooling time, and preferably it is, it has to be a cooling time of the mixing phase because that's the most relevant phase, and the flow timescale
09:44:02 scale is nothing, depending on nothing but it's the time scale for turbulence depending on the physical setup and damn color number is nothing but, the ratio of the reaction time scale to the floor time skin so can we sell more generalized all this criteria
09:44:17 based on the physics included in the setups, let's say, in New York is cooling and the flow timescale What do you think, um, yeah I think you reiterated exactly the point I was trying to make you know when I ended on the mixing timescale that's that's
09:44:33 really exactly, exactly the point yes that if the cooling time is less than the mixing time the Eddie turnover time or the ratio of the two which is quite similar to the dumb color number, then I think this, this is a great way to look at it in, you know,
09:44:50 in general across all the different systems it's, it becomes a little, you know the reason why I wanted to put it the way I did is because when you're talking about, you know, thermal instability in the stratified medium it's not.
09:45:03 Yeah, mark is making a point in the chat right now.
09:45:08 Gravity changes things pointy waves gravitational gravity waves rather are different so it's, I tried to be a little more abstract but I think you're you're hitting the nail on the head really, I'd love to hear what Max, or Brent has to say about this,
09:45:22 or critique to just one point I just want to add one point in that case, if there is gravity or let's say there is magnetic field or let's say there is thermal conduction or cosmic rays I think the reaction time scale would change, it would just become
09:45:39 a function of all those all the non dimensional parameters which relate to those physical effect for example, here the reaction time scale is equal mix, which depends on the cooling function at the at the intermediate temperature to be precise, I think,
09:45:54 in that case, that would be a function of all these parameters.
09:46:00 Do you agree with this point.
09:46:05 How about how about we hear from Max.
09:46:09 Yeah, I mean, I mean I think you know like I mean we will have a lot of interesting discussion in about related fields and so on in the non thermal week I'm pretty sure but that's I don't know how much we want to get into this now but, I mean, delay for
09:46:25 non thermal delay the right.
09:46:31 But I think your main point, a certain.
09:46:34 Good. What can I say like your main point I mean was.
09:46:39 It was, it was along the lines also but Marcus mentioned earlier right at this point I think they're just great analogy So, can
09:46:53 I since there was a question directed at me. Right.
09:46:56 Yeah. The reason gravity is different, is because it makes what's going on depend on the macroscopic environment. And so, When a medium is stratified.
09:47:09 Then what's happening. depends on a larger scale conditions. Okay. And that's different from all the different other things that can happen on the micro scale.
09:47:23 I also have want to respond, CT mix is something which is, you know, we cannot, we cannot get it a priority. Right, it's good to think in terms of, you know, it's a good physical quantity, but it's an incredibly difficult quantity to measure, because
09:47:42 it depends on how mixing is driven is it through thermal instability or, you know, penetrating filaments, so we need something which is more measurable and more physical, and eventually of course it leads to turbulence and mixing.
09:47:57 But, you know, we have to sort of distinguish the physics of it and you know the, and how it is actually driven, given a set up.
09:48:10 Thank you.
09:48:12 Said critique Thank you.
09:48:14 Okay, so I have seen Joe McNally with his hand patiently raised for the last 20 minutes or so go ahead Joe.
09:48:22 Yeah Thanks Hi, Joe Hello everybody, UC Santa Barbara.
09:48:45 So, gentlemen, first of all amazing talk, I think it's cool that Chris is here because obviously there's a clear arrow of progress from client McKee at all 1994 where the these sorts of first idealize calculations of cloud crushing etc were being done.
09:48:44 My question is how for that for the entire panel is, how do we build a bridge from all of this. All of this I, all these idealize simulations where we're actually really the resolving the physics and learning a lot about the physical processes, whether
09:48:57 that be crushing or condensation etc growing, growing small scale structure or dissipating small scale structure and like the cosmological simulations that come nowhere near resolving that structure in other words if somebody claims that they get the
09:49:12 covering factor of silicon to absorbers right in such and such cosmological simulation. So should I should I believe that should I not believe that, how do we build that bridge.
09:49:27 Um, maybe I'll start. So, you know, to my mind, there's there's, there's two directions.
09:49:34 One is you know people are throwing more and more resolution out in the CGM right in these cosmological simulations, you know look at Dylan Nelson, and the rest of the tangi 50s group look at, you know, Tempest and foggy and Frank have onboard simulations
09:49:50 and so there's lots of stuff out there and I think there's a lot to be done with very careful analysis of those simulations to see if the processes we're seeing in the idealized setups translate in are at play in those simulations.
09:50:07 You know I think Dylan and critique just did a nice look at this in the of the code clouds in the CGM of lrG galaxy so that's, that's sort of one direction to go it's to try to push the CGM to higher and higher resolution in cosmological simulations and
09:50:23 make a connection there and then I guess I'll, I'll echo Cameron humbles his point from the chat room and he says, answer, colon, sub grid models. So, Cameron has been a big proponent as have many of us about actually coming up with a sub grid model for
09:50:44 the sort of unresolvable or incredibly difficult, difficult to resolve cold phase in the CGM, so maybe that's what we need to do is just say punt. We can't get the hydrogen MX right, while still getting the global dynamics right so so let's move it all
09:51:00 to a sub grid model, I think, Neil cats and his student who I'm embarrassingly blanking on just put out.
09:51:07 I think one of the first attempts to start to do this. And there's many of us working on this on this now so I would say those are the two Pathways Forward that I see and I think, because I think you've really address a key question for the theorists
09:51:22 is what can we have to bridge these two worlds. Just one one small follow up which is so how, what is the minimal resolution I guess this is the thing I'm trying to understand is how far away are we from this i'm not i'm not discounting that that the
09:51:38 the cosmological simulations that load all this resolution into the CGM I think those are incredibly important but just how close are we.
09:51:48 Yeah. Can I talk. Okay, okay. I think this is directly related to the point that I brought up earlier about which size scale we care about. So I think that if the CGM is truly a mist right there aren't big clouds, everything is in tiny droplets.
09:52:04 Then there's no getting around it, we have to have a sub grid model. Right. But if the CGM is actually composed of much larger scale structures, and they have some, they have some small droplets, you know, within them or surrounding them but that's not
09:52:18 what's determining the both dynamics, or say the covering fractions, then maybe we're almost me maybe TMG 50s there, right. So, so I think that that is a really important question because I think that it's essentially you know which size scale Do you
09:52:34 care about do you do you care about the smallest sizes or you care about the the bulk structures.
09:52:42 And I think that, you know, if it's the bulk structures that in some sense that this is going to be easier, but we don't i don't think that we know at all and that's why I made the point that I think it's really interesting that so far from the theory
09:52:54 side I've not seen evidence that we should believe that it's the tiniest scale that matters.
09:53:02 At least for, you know, understanding the properties at the CGM.
09:53:07 Oh well, I think I just showed three plots that show that we do need to resolve GST cool if you want to get the face structure correct if you want I mean, there's been all these questions about pressure equilibrium.
09:53:17 And so if you want to make a detailed observational prediction and prediction, you need to get the face structure right.
09:53:25 If you want to get total amount of code gasp below, 20,000 Kelvin, that might be easier. I know, so I yeah I will I will retract not retract but but weakened my statement by saying it 100% the answer depends on the question you are trying to answer it.
09:53:44 Yeah. Are you fed me, please. Yeah, I just want to also dwell on the point that if you want to compare two observations, I mean, I'm interested in lemon author radiative transfer or lemon continuum escape for instance I think these small structures are
09:53:59 very important right so so if you're interested in just the total cold gas content I think Frank if I'm to forgive a very nice talk here at can't up if you're in this multi Facebook show to show you know that even in this enhanced resolution simulations,
09:54:14 they are not Converse yet on this call structure and and in from the theory side I would say, you know, we know that at least we don't have to resolve the field length in order to get this right.
09:54:26 But, but to just make one extra point on you know that it's not just the size of this just called gas structures I mean in these turbulent boxes Drummond was showing i think but it's also important.
09:54:36 You know is where basically your turbulence pulls off because of your numeric right and that's not the syllabus, that's in fact, you know, many times the cell size right so I'm actually quite worried about you know and simulations, we are also running,
09:54:51 and that you know if you if you maybe keep cold gas small cooker structures artificially because of this attack because your dissipation. You know numerical dissipation scale there is much larger than your new yourself with.
09:55:03 So that's something to to care about so to just answer your question, Joe, I think, you know, like cosmological stimulations not resolved in this total called gas mass as for occur showed, you know, not, not even sure if our simplified turbulent boxes
09:55:23 but sure about the turbulent mixing layers, sorry, I just want to point out there's a lot of really good stuff happening in the slack, but there's some interesting stuff happening in the zoom chat to the people who are typing these very substantive you
09:55:36 know remarks in the zoom chat, I encourage you, Joel Bregman especially Claude Andre Martin. Go head over and put these in the slack. That's where these comments are going to be preserved and commented on asynchronously by everybody who's available at
09:55:51 the top today we don't have infinite time, go over to the slack. One more announcement, a drum and referred to an after party in the hotel lobby Just kidding, um,
09:56:05 the after party if you want to know the details I guess head over to Halo 21 precipitation channel on slack where the details have been posted that's a half hour we have four more minutes to people have been sitting here with their hands raised for paid
09:56:18 patient, you know 30 minutes or so wrong man Kartik, I'll take your questions and then we're going to conclude our plenary discussion and thank everybody again but wrong.
09:56:28 Go ahead. Thanks just, I just want to push back on your comment actually on the slack that we have somehow or observations are lagging behind theory, right, as a lot of pushback it's maybe my observer bias, but I just want to point out that we have a
09:56:42 fantastic laboratory, right next to us the Milky Way, which is amazing. For some, you know, small scale distribution of guests for example the Fermi bubble perfect example of multi phase out flow where we have hot gas.
09:56:58 We have hundreds of cool resolve clumps seen by this incredible paper been recorded to leader and collaborators of 21 centimeter cool gas, which also exists in molecular gas which kind of goes away after a few people process.
09:57:12 Then we have the UV absorption we see in train gas. So, there is a fantastic reserve or observation that exists, which I hope the theorists will look into to compare their predictions.
09:57:26 You know how it kind of attendees up like journals beautiful simulations the beautiful.
09:57:32 The 2d laminar flows, do you actually can make predictions like we've seen the Fermi bubble might be a great place to compare and try to constrain them perhaps.
09:57:41 All right, thank you. Rama, I think you just volunteered yourself to sit on a panel during Milky Way week. And of course, most people here know I agree with you about the Milky Way being the best galaxy, there is a halo 21 Milky Way channel, by the way,
09:57:55 where I think a lot of the future of the CGM progress observational progress is going to happen, however that channel if you're interested Milky Way week is week four.
09:58:03 Don't forget, okay, Kartik.
09:58:06 Hi.
09:58:08 So I was wondering you know he talked about all this. Importance of cooling in the mixing layer.
09:58:16 I mean, the radiation that has been cooled. Now, we're assuming that we all take when they do hit Isagenix simulations that you know they just leave the system.
09:58:25 So I was wondering how much radiation does it, you know, get out of this box I mean, how much radiation. Does one system go out is, can it be a significant source of ionizing radiation in the CGM or in the, you know, our GM.
09:58:44 So, how much of it is coming out that the, the question what fraction of the kinetic energy is related.
09:58:56 As we know if the radiation.
09:58:59 Boy, this is like a qualifying exam right now I'm trying to like do the math in my head really quickly i think i think i think this is a really a really interesting comment you know and protect you know when I hear that I think okay so we have options
09:59:14 six it's admitting really short wavelength photons and that could then ionized nearby.
09:59:21 You know, neutral hydrogen or something like that and I remember I had a conversation when I was visiting you guys that I see with the mon not about this exact question this is now four years ago, and I still I still don't have a good answer so I'd love
09:59:36 to hear if anyone else here has a good answer and maybe we can follow up with this over, you know we should start a slack thread on this so we can. And that's exactly what context, would you mind starting a slack thread on this exact question so that