08:32:25 Excellent. Chris, take it away.
08:32:34 Alright, so I was asked to talk about observation estimates essentially this size scale structure, and the CG and and so we're going to talk about.
08:32:42 I think we're going to start first with whatever we actually measuring here, and then go through a number of approaches that are available to make some estimates of the size scales of structures in the CG Now, a couple things.
08:32:53 Firstly, I'm also going to talk to them spend quite a bit actually on the Galactic instead of me because there have been lot more measurements in some regards in the galactic center so even plus the precision that sort of measurement scale on a smaller,
08:33:04 but also I. This was is not my area in some ways it's something I've worked on before but please do not be offended if you don't see a similar result up there and let us know we can talk about it in the breakout room.
08:33:18 So I guess one thing that struck me when I was thinking about this was, I mean we have to discuss at some level what we're measuring and typically the way that many of these measurements are made.
08:33:28 Is it we're assessing something scale over which the competencies or perhaps the kinematics vary in some significant way and that that significance. What we mean by that varies from measurement of measurement.
08:33:38 The other thing is, even when we're doing direct imaging of clouds Rafa measuring some sort of size of a cloud and that definition can be nebulous there are some when you have an h1 de de que, you're able to define that a little better, perhaps, but there
08:33:53 are definitely definitional aspects of that, and it often will depend on angular resolution and comments the sensitivity and Mary Putman talked about this in, with regards to the competency and Bejeweled extreme results.
08:34:06 A couple weeks ago.
08:34:08 So, if we started the Milky Way.
08:34:10 There are sort of some primary ways in which we get information about small scale structure in interstellar, the Milky Way. And they rely on thinking about the spatial sensitivity of spatial variations in column in cities, or at least from the absorption
08:34:26 line based methods that rely on either one of two methods one is thinking about temperature variations, where you have a background source that's moving with respect to a foreground cloud, the cloud can have some motion as well.
08:34:38 And, and this can even take the form of binary star, because the binary is it goes around its orbit you're probing different sightlines to the foreground anyway so that puts an upper limit on the size scale of the structures, you probably know this essentially
08:34:57 twice the orbital simulator access of the binary. And some of this has even been done for example in the radio using pulsars is the zip across the sky and we can see absorption of 21 centimeter it hits the ball starts to give us some estimate of the changes
08:35:07 in that column, or that absorbed.
08:35:10 Optical depth as a function of time.
08:35:13 The other is to rely on spatial variation so you're, you're measuring multiple sightlines through some foreground cloud. And this was kind of first done in the 50s actually but there's a long history of doing this, both in the Milky Way, and thinking
08:35:25 about multiple segments the queen of swords in the CGM of more distant galaxies.
08:35:32 Now I should point out that there is a really nice job of sort of micro structures and diffuse Interstellar view the Milky Way by snares and lm that appeared in 2018.
08:35:43 Now they're talking about size skills of not only subpar sec but sub au in some cases that we did sensitivity to the TSA S is tiny scale atomic structure here, CNN stuff is sort of the sodium, one of the things that you would pick up and absorption.
08:35:57 And then, extreme scattering events come from.
08:36:01 Usually studies of pulsars and such. So between simulation and measurements of for example the optical depth of each one against radio lobes, and how that changes in time and space, and even the temporal type variations that you can see sometimes here's
08:36:18 for example up some of the work by date Meyer showing the absorption from this specific cloud that we know to be a foreground, very small scale thing in the local bubble that period in time.
08:36:30 So, these micro structures that get discussed in here are typically thought of is either tracing the turbulent cascade of energy, down to very very small scales within thermal instabilities and they're often found to be over pressurized with respect to
08:36:43 their surroundings so they're, they're perhaps transmitted in some ways, I'm not going to discuss a lot of that because that gives way down on the size scale.
08:36:51 But there's another reason for not spending a lot of time on it so this is just to focus on some of the stuff that the northwestern group led by Dave Meyer did over the last few years and.
08:37:01 And one of the things they did was taken, if you the dense packet, which is, you know, 10s of seconds on the side essentially I'm just pointed out a globular cluster, and look at the variation in the column density of sodium one as they look across that
08:37:15 cluster and what they find is factories have to type variations in those comments that he's over sort of a few thousand eight you type skills.
08:37:24 It's not ubiquitous in the sort of total amount is, it depends on which direction and looking, but in a couple of your clusters we've seen this with some regularity.
08:37:33 But part of the reason I'm not going to spend a lot of time on those sort of very very small structures, is that the thinking at least in the Milky Way crowd right now.
08:37:41 Are we starting to standing of it, based on things like binary stars that are separated by a few thousand to you.
08:37:54 Is that why we see these variations in the cold neutral gas, the very very dense as cool as gas, and in the non dominant ionization stages of guests such as sort of one carbon wings you want things like this.
08:38:01 That changes, don't seem to be present to a large degree in the dominant ionization stages that we see things like that, we're used to seeing in the lower hands things like zinc and magnesium and such.
08:38:13 And so, it seems that the structures in the wonderful medium are significantly larger than this few thousand 18. Now again, part of this depends on what your definition is and how we're measuring this book.
08:38:25 It's important remember them all we're doing some level is seeking and looking for, and in some cases measuring column and see variations over some spatial escape, but it doesn't seem like those are our predominant or particularly important in warmed
08:38:40 up.
08:38:42 Now, in the local group and little beyond we can actually do direct imaging of clouds that gives us some handle on size scale so this for example is a look at one of the tangent.
08:38:51 Tangent point velocity. So we have a distance to the gas.
08:38:55 Just a section of the attendees can pick disk in the interstellar medium. We saw this earlier from July, but also showing the Smith cloud.
08:39:04 And typically what we find in the Milky Way is that these each one clouds or they're likely cloud complexes with some substructure that's just not quite resolved cure we're we're, we're not measuring the find scale structure but typically sizes are of
08:39:16 This is again showing the work by shoe at all from 2011 The Mary showed him and one thing I want to point out here is that, you know, these are probably pretty reasonable sizes that get measured you know again a few 10s of parsecs it at complex see because
08:39:33 the resolution is very far down here, but we also do find that as Mary emphasized to in the word Piper Walker and some others that as you go to interferometry data, and you look, you will find structure on many many skills as you go further down so this
08:39:47 is sort of a definitional
08:40:03 I wanted to have a brief interlude here to for just to talk about the 31 and 33 system because this map by Brandon Joker that came out in the early 2000s has been mentioned a few times over the last couple of weeks.
08:40:14 And, one has to be a little cautious with this because so they image the in 31 and 33 system using Westerbork and, you know, total power mode and effectively use sort of very large spatial skills and very large velocity skills, it turns out to integrate
08:40:28 in order to get to very low cognitive. And one of the things that happened in that case was they picked up both some residuals emission from the Milky Way for in the in the special direction but especially in the velocity smuggling the that they did that
08:40:42 brought in a mission from the side lobes that looked like it had the right velocities to be associated with him 31 and 33 system. So a lot of this material is is not quite real anymore.
08:40:56 And in fact, when you do see the stuff that is real. It is much much smaller scales that will be implied by the structures that you tend to pick out in the so this is where by city Wolfman, and others, and just showing that, you know, again you, you can
08:41:12 resolve some of the submission into extremely small clouds from the standpoint of the scale that was shown here. But even, even though it's like we have substructure that we're not quite measuring you.
08:41:24 I will say it is possible then to in the sort of warming to medium and a little bit of a cold neutral unity by galaxies look directly at traces of that either an HR for for the warm ionized medium or in things like that dust structures that you see in
08:41:38 the thick disk of john spiral galaxies and such, and we typically find that, again, once again, you know, typical structures, the smallest clouds, probably resolution resolution limited statement have, you know, a few to, you know, a few 10s of parsing
08:41:52 type scales. And this complex is the host how's them, have you know sort of hundred times to almost killer carsick timescales.
08:42:02 All right, if we move on to the transition temperature yeah so this is sort of guests respect who was sick carbon for perhaps in such, it appears that the transition temperature guests nuclear varies on sort of 10 to 100% skills and that that statement
08:42:15 statement may be a function of the alien that you're actually using the protest just because they probe different energetics in the Milky Way.
08:42:22 Certainly we know that the transition temperature gets traced by oh six at least has structure on degree type timescale.
08:42:48 Link skills, angular scales.
08:42:46 At long highlighted to sightlines but not augmented type skills. So we have many years ago, use the data that in the large and small metal in the cloud to measure all six coming from the milky way towards a few 10s of stars. And we didn't do that and take
08:43:00 50% variation on all the angular skills throughout this essentially the dispersion of those six competencies in the Milky Way is about 30 to 40% so there's a lot of bouncing around, even in this relatively small angular part of the sky.
08:43:11 Variations of seen it all velocity that includes both the low velocity guest interview velocity as high velocity. So, there is a lot of structure in this.
08:43:20 When you do a, an auto correlation you find there's no sort of preferred scale for this down to the smallest skills that we can measure. Now, if you make the assumption that that all six resides within about five kilowatts activities, which is kind of
08:43:33 what you expect for high velocity clouds and such.
08:43:36 And it's a few times as typical scale height that's calculated for the action and six in the Milky Way, then the skills that you're talking about here are sort of less than a few 10s of course it's typically.
08:43:46 Now I will say, we tried to do this on an even smaller scale where we use these. I love this we use post extreme horizontal branch stars in in this globular cluster.
08:43:55 This is an ultraviolet image from the UAT instrument the pool on the shuttle, and we at this distance each of these stars, one arc minute is about a killer par six separation so we were probing skills down to about two to 10 kilometer six or so, and we
08:44:09 didn't see any evidence for any structure in the oh six on with sort of variations on the 25% level or more on the sort of less than 10% scales know we don't know exactly where this guest is it besides the velocities that probably place it in the disk
08:44:33 the low thick disk of the Milky Way, certainly no larger than the height of this globular cluster which was about two kilo per 600%. All right, and there's one other way to sort of estimate the scale of oh six in the Milky Way that I found really interesting.
08:44:40 One of the things that happened was fuse had two apertures well three episodes but two that were used it on for really bright stars you would use sort of a slip by capture and that left your large 32nd temperature pointed in some random direction in the
08:44:52 sky. And because of that people then Dixon and Robbie sacred and others, put together all that those data that we're just making skin blink sky observations throughout the galaxy, and look for options six to few sites in 16 and mission from the Milky
08:45:04 Way.
08:45:05 And there are a couple of ways in which they estimated the size scales of the immediate regions. The first was, if you just do this sort of standard thing of saying we'll look you know the mean density is something like the admission measure over the
08:45:27 density and if you divide the column that's you by the mean density. So let's comment c squared over here, you get some measure about like scale, as long as you're sort of assuming that the conditions don't vary by some huge amount there. And they did this all over this guy in there sort of 30
08:45:30 all over the sky in their sort of 30 detected regions, but in particular in a couple of directions that sought admission from complex See, and the measurement extreme, they can make some crude estimates of what was the the sort of typical length scale
08:45:43 of the meeting regions and they come out to be of order again tend to maybe 100 part six or so depending on the assumptions that you make it a little crew because they didn't have absorption measurements along exactly the same sidelines but you know of
08:45:53 course.
08:45:56 You do what you can.
08:45:56 Now the other one that and I have to say I've talked to them about this measurement since and while it comes off is very positive and robust in their their paper.
08:46:05 There are little dodgy about it now when they think back on it but one of the cool things that you can do is fuse has an aperture size of about 30 kilometers per second.
08:46:12 that you can do is fuse has an aperture size of about 30 kilometers per second. And when you involve that the essentially square, had widespread function you can get from a pure 32nd wide aperture with instrumental spread function, you should get a line
08:46:25 that looks something like this it's sort of a Gaussian coupled with the touchpad, and it should be about 100 kilometers per second across. And what they found was it in about a third or so of the directions where they detected oh six and a mission.
08:46:37 The, the width of the mission lines that they detected was smaller than they would expect for a completely filled aperture. And so if you make some calculations to say what fraction of the aperture we have to be filled in order to get the lines as narrow
08:46:49 narrow as we see them. They come up with some extremely small size here so if you the you know the typical size gala they measure something like 20, seconds, across and stuff, but the for 30 seconds of being.
08:47:01 And if you think that that sort of gives you the full size scale of the less than you know sort of a 22nd war zone size for the 6 million reasons that they're viewing.
08:47:12 You know, these can potentially correspond to some very small size skills. Now, this is at some level intensity waited measurement as opposed to, I'm sorry, did c squared way to measurement as opposed to a density where the measurement like you might
08:47:23 might otherwise get, but nonetheless it's kind of intriguing that there may be some extremely small filaments, even in the sort of transition temperature regions that in order to be excited have to be pretty much at 10 of the food Kelvin a robot.
08:47:38 Alright so if we move out then to think about what we learned about the CGM from from Quasar absorption I think so, I mean, a lot of us were introduced to this idea that Michael route and the work that he did over the years.
08:47:48 You know he he started looking at, and other people have done this before but I think this was sort of when, at least it got into my brain, it was because of my age or something but he started looking at lens quasars and looking at the structures in the
08:48:02 museum two systems in particular. And this just shows a series from from this famous Einstein Cross of sort of a redshift of roughly a half system. And what he argued was that look you can trace the complexes of magnesium to over, you know distances that
08:48:19 are sort of half a kilo person to kill or something like that so complexes are correlated on large scales, but the individual cloud that so looking at the individual components in here for example are difficult to trace over more than a few hundred, or
08:48:42 Now, this distinction about this, you know, these are customers data that this distinction about how you, you look at that absorption lines like this, it can actually ask if they're changing both in velocity, and in, in total column is your equipment
08:49:01 might get lost at low spectral resolution so it's something to be aware of as we move forward with one of the work that we're doing with if us. I should say to there's some been attempts to, there have been some attempts to do this via temporal changes. The, there was a, an upper limit for the localization stuff and art, back in the
08:49:06 the localization stuff and art, back in the 80s published a potential sort of case of each 120 percent of your variability on sort of, you take times with skills based on timing and but they were never quite clear what the origin of that was.
08:49:19 There's been a lot of work done. More recently, looking at sort of wins quasars to prove foreground CGM and in other galaxies and, and a lot of the time, just depending on the separation of these places but but typically when we're able to do this.
08:49:34 Most of those are sort of probings five to 10 type, type, type skills so again they're telling you about large scale correlations of the absorption, but but they're not often given quite as much information about the very smallest case.
08:49:48 If you go from the low ionization state absorbers to the more higher to the higher ionization state guess. This serves another plot, plot from another rap paper in the late 90s.
08:50:00 And what you can see is in the carbon two and silicon to, for example, there's, there are components that come and go in various ways. But the carbon for in silicon for tend to be much more in agreement between the two sites and then in fact he has this
08:50:13 nice part of. Essentially, the fractional change in the competency is a function of the transfer separation of segments, this is even just from one site line of course for gravitationally means quasars that you're seeing different separations depending
08:50:26 on Richard, but you'll see you don't get maybe 250 percent type variation, for the most part, until you get above a particular carsick or so.
08:50:34 And this comes up to with action sticks in there this is a paper from Sebastian Lopez, it shows in black and blue here, two different sight lines for various redshift This is actually six and absorption, and they also were arguing that the quote unquote
08:50:54 coherence link of the action stick should be bigger than a particular parsing.
08:50:52 Keep moving into 2018 paper had a nice little summary of sort of the picture of this. On the left is the fractional difference in the equivalent with coming from magazine to Ryan tune so low ionization stickers.
08:51:04 And on the right there you see the same quantity for carbon for now I should say, is as you get lower on this plot that means a larger difference between two sightlines pro by gravitation admins quasars.
08:51:18 And what you can see is in the low ionization state guess at all physical scales there's sort of a lot of, you know, it's sort of filling this whole space.
08:51:26 And when you go to carbon for though, as you look at those small physical separations there's a lot less of this space occupied. Okay and so that's just it's just implying that the typical cycles are which carbon for varies are somewhat larger than you
08:51:48 see.
08:51:43 So, last two things here let me talk a little bit about density estimates, their density based estimates for science skills that come from photo ionization.
08:51:50 So, these, these all are going to depend on the assume radiation field intensity in particular, but if you understand that you can make some Catholic good estimate for the length of your, your sight line through a bit of low ionization Yes.
08:52:06 Now, It's a little.
08:52:08 Well, but let's look at it this way, if you think about this as sort of a quote unquote realistic cloud or structure where it has some density variation within it, maybe a high density core and some lower density in the, in the way.
08:52:21 So, the density is a function of distance might look something like this. In the core competencies Hi, you're going to be, you're going to prefer lawyer positions that gas and it's the density goes down again prefer higher annotations that gift.
08:52:32 Now when we do the modeling for this most often not always but most often. We're sort of taking that core of the low ions and we're saying, okay, we're going to model this as a constant density structure, and it's going to have some links that goes through
08:52:44 it and.
08:52:46 And in order to sort of account for the way in which we're cutting this out we're only going to take out the lowest ionization or some mixture of ionization states that we think occurs in this this high density core of the, of the structure.
08:53:00 So our model structure is a very, very, very much simplified version of this.
08:53:05 And then we're going to say well look the link scale, we can calculate by taking some money on and measuring its colonising dividing that by the model based column did or density physical density of that I on.
08:53:17 Now typically if you did something like this that for each one you say what we measured each one competency, our model gives us the particle density, and then we have an ionization fraction we also has to have to include in there in order to turn that
08:53:29 sort of total particle density into each one particle density. Now, because of the way in which I mean really when we do these models were trying to imagine ionization parameters, which is the ratio of both tendency to particle density.
08:53:42 And so your density that you get and here, down here for the model and some level, depends on your normalization of intensity in the photo IDs radiation.
08:53:53 But nonetheless, some of us have been brave enough to actually you know present the results from it so Jess has been sort of brave enough she she's shown this in a number of conferences, but it didn't get into the paper so this is the link scale for sort
08:54:04 of the photo monetization model and it comes from the cost heels analysis fires, so he plotted or showed this as a disease of functional competency for the cause allergies are really the key and show when that up.
08:54:18 And you can see lines of constant link ceiling here. They give a sort of typical length of about 100 parts six or so for the models that they have. And then, Nico and collaborators in the CCC survey of a PDF essentially have the link scales are involved
08:54:36 in their modeling a blind limit systems and partial management systems so that the sort of takeaway from this is that the little ionization stick case has scales of order, and I'm going to say of order point one Do you know even 10 to the power six if
08:54:48 you sort of take the 60% confidence intervals here for example, but you have to remember too that this really is dependent on what strength of the radiation field.
08:54:59 And then lastly, just a couple sort of a hodgepodge of some things that I found really cool that I was in some ways less aware of as I started to put this together, there's some evidence from the fact that if you look at the continuum, the incidence of
08:55:12 managing true absorption systems against the continuum of quasars which arises in sort of a very narrow range of the accretion disk versus the incidence of magazine two systems that you see if you look on the, on the broader mission lights from quasars
08:55:27 the statistics of those counting are the same. And so that tells you that gives you an estimate or sort of a lower limit on the link scale of the magazine to absorbers which is bigger than about a few thousand kilometers or 2008 you rather keep Rubin
08:55:42 has a really nice paper where she's looked at essentially the incidence of managing two systems against background galaxies and ask the question How big are the background galaxies have to get on the sky before you start to get statistics that are different,
08:55:55 that you get for sort of quasars, and that tells you something about the again what they refer to and we often talk about is it coherence live with these it, it's not necessarily telling you the sizes of the individual clouds I'll do with me.
08:56:16 you that the sizes of the structures are the correlations of magnesium two systems on the sky and they get a number of about to kill Part Six and more. And then, Jeff cookie and john Romero did this thing where they essentially look they found a deployment
08:56:21 of a system that gets the background galaxy and looked at whether essentially what the covering factor of that template in London office system was against the background galaxy.
08:56:30 And they, that gives you an estimate of the area of that absorption which is a few to, you know, 100 square to the projects which is quite a bit but again this is more of a complex level idea.
08:56:43 And then last 15 and proliferation recently of lots of measurements against arcs and such, the strong gravitational lensing and clusters, with the, we can measure the magnesium tool is a function of impact parameter or even as an from from galaxies.
08:57:00 And this strikes me is extraordinary because if you look at this platform the most recent Sebastian Lopez at all, paper, the magnesium to fall off from this individual CGM sort of follows what you get from sort of ensemble surveys of managing to absorption
08:57:19 around galaxies. It shouldn't work that well it shouldn't be kind of a monotonic fall off I mean it should be more bizarre and random than that. and yet it is this very recent paper by Chris Mortensen and collaborators also find the same thing.
08:57:32 These are the green points here is the Lopez points around the black there so again what that doesn't tell you so much about the very fine scale of these many increases and what it does tell you is there a correlation some pretty large scales that are
08:57:44 important.
08:57:46 Alright, so I'll just summarize here. I don't worry I'm on time so I hope I didn't go over too much but in the Milky Way, you know the CNN the non dominant position states certainly very odd extremely small scales.
08:57:56 The one neutral medium guests though tends to be or at least have consistent column that says across sort of 10s of parsnip type scales. Even though within that they're probably things were missing that relatively smaller scales.
08:58:08 When we look at the transition temperature gas. It seems like the skills that are important they are sort of 10.6 and above. And, and you kind of see a similar behavior as you go to some of these larger scales in the CGM are in CGM measurements that you
08:58:24 know as you go from the magazine two systems a higher end ization state systems, you go to smoothing over larger scales. Certainly we know that there are, well, we think we know there's not structure on well below of course tech in medicine two systems
08:58:40 but the thing that sort of intrigued me is there certainly coherent over very large scales, even if we're not.
08:58:45 We don't see them very often sort of the smallest skills that we're looking for. So I'm happy to answer questions and thanks for Thank you Chris Yeah.
08:58:56 That was a good comprehensive overview and really just, you know, covering every size scale measurement of the CGM and more, and the ASM.
08:59:08 We that was about 25 minutes, so we won't take questions, except in the breakout room, but I this is our time for a break so at 9055 after the hour we are going to start john Davis's
08:59:28 here in clearing tutorial. So, you know, take a break or go out, go to the breakout room with Chris.
08:59:39 And that was a very intense first hour so excellent job by everyone.
08:59:47 Thank you.
08:59:49 So we'll be back here in about a little bit less than a little bit more than five minutes.