 So I will be talking not about astroecology today, but about star formation in the centrum like of the zone. So the inner few hundred par six of the galaxy. So I'm going to have two main topics. So first of all, I'm going to talk at large about star formation in the central zone. And then I will share with you this Alma large program that we were just talking about before called ACES, the Alma CMZ to try and understand star formation and feedback in the CMZ. Now, as this is a talk as a part of the CTA webinar series, I'm going to concentrate really on two main themes throughout the talk. So the first I'm going to try in this very broad umbrella, I'm going to focus on trying to link star formation and feedback in the CMZ with this idea of the extreme universe and the sorts of extreme phenomena that you're going to be observing with the CTA. Then the second part of the talk. So as well as telling you why we're so excited about this ACES data and why we think it's really going to make a step change in our understanding of star formation and feedback. I'd also like to encourage people to actually to join the project. So this is ACES is open to anyone in the galactic center community who's interested. And I think there's, as I hopefully I'll show later in the talk, that there's a lot of overlapping the sorts of science questions that we're asking. It'd be great to have input from members of the high energy community so that we can make our data as useful as possible and hold some of these science questions together. Okay, so on to the first part of the talk, star formation and feedback in the central leg of the zone. An outstanding review written on this topic by Johnny Henshaw and collaborators. So this is a review that's part of something called the Protostars and Planet series. And in planet formation and star formation, this review is held every seven years. And every seven years, the community gets together and they pick a small number of reviews on key topics. And Johnny is leading one of these these topics. And a lot of what I'll be talking about today is summarized really nicely in his review. And I would encourage you if you're interested to contact Johnny about this. It's really an excellent review. I should say that a lot of the slides I'll be using, so the really nice visuals and things were made by Johnny for this talk. Okay, so to go to this is a very broad topic, star formation and feedback in the central leg of the zone. So I've broken it down into four main themes or topics. So I'm going to start really quite briefly with this is a broad big picture context. So why do we study, we've already touched on this in the introduction to this talk, which is spot on. I'll just kind of go over that, maybe flesh it out a bit more, and why we're interested in the centers of galaxies and why the CMZ, why our own galactic center in particular. And then I'm going to dive in a bit more detail to our current understanding of star formation and feedback. So I'm going to do this by explaining this long standing puzzle that we have in the galactic center and that's that when we look at the star formation rate, it appears to be much much lower than we would expect, given how much dense gas there is. So I'll sort of dive into that, explain this puzzle, and then I give you a flavor for where we currently stand in trying to address this puzzle. Okay, so then why are we interested in galactic nuclei? Well, this whole talk series is on an extreme universe. And I don't think there are many other places in the universe quite as extreme as the centers of galaxies. I think we can all agree on that. Obviously, they host supermassive black holes and, you know, even in and of themselves, they're some of the most extreme objects in the universe for testing GR and so on. But surrounding these supermassive black holes, the centers of galaxies have huge gas reservoirs and these huge gas reservoirs produce lots of stars. In fact, the centers of galaxies can account for up to this sort of the prodigious outflow and feedback and energetic activities from supernovas and wind and so on and can play a key role in shaping galaxy populations. So I think it's fair to say that the centers of galaxies, and really as we look out into the universe, try to understand why it looks the way it does, then the centers of galaxies have played a key role in shaping that. So what about our own galactic center? What can we, what role can that play in this sort of trying to build our understanding? Well, I think the single main thing, certainly for me that makes it stand out, is it's the only place where we can really zoom in down to the scales of individual stars and follow the gas as it flows down into the central supermassive black hole. Now for other galaxies, we can get a great understanding of things on sort of kiloparsec scales, maybe from nearby galaxies down to 10 parsec scales. But what's driving these huge, like these energetic processes, these galactic scale outflows are driven on sub to the 10th of a parsec scales and really all the way down to thousands of AU where these energetic processes are being launched. And within our lifetime, the center of our galaxy is the only place that we're going to be able to do that. It's the only place we can link the kiloparsec scale galactic processes that drive things down to these small scales. And then when we, when the feedback starts, we can follow it back up again. So that really is unique. And we have to base our understanding on the center of our galaxy. Now, not only that, that's kind of baryonic processes. But of course, like one of CTA's key science goals is looking for possible evidence of dark matter, maybe self-annihilation signals. And the center of our galaxy is a great place to look for this. I'm sure you're all familiar with the galactic center. So the gamma ray excess is obviously debated, the origin of that. But what is clear, no matter what you think it might be, is that if you want to look for dark matter self-annihilation, you've got to get rid of the contaminants. You've got to get rid of the other stuff that was interesting for me, but is garbage and that you need to get rid of looking for dark matter signals. And of course, the center of our galaxy, we can resolve individual contaminants. So I think it's clear that the understanding, hopefully that's a big picture, it's clear that understanding star formation of feedback, and it seems it really is important. So I think that's why this long-standing puzzle continues to draw so much attention. So I'll explain what that is. Well, when you go out and you take any telescope and you point it at the center of the galaxy and you measure how quickly it's converting its gas into stars, you see that it's doing it much less than you would expect. So typically the star formation rate is one to two orders of magnitude less than you'd typically expect. So why is that important? Well, if we said star formation of feedback in galactic centers plays a key role driving galaxy evolution, so if it's different, if star formation feedback is somehow different in extreme environments like the center of our galaxy, it's crucial to understand how and why. So I'm going to spend the next few slides kind of diving into this puzzle. We're going to start I'll give, I'm not sure if everyone's familiar with the galactic centers, I'm going to start by giving an observational, very brief overview of what the center of the galaxy looks like, what kind of phenomena happen in there to get a feel. Hopefully that'll be helpful for the rest of the talk where we start looking at the physics. So we'll have an overview, then we'll look at how we derive star formation rates before we go on to explain why it's lower than expected. What does expected mean? Okay, and then finally once we've done that, I'll bring it all back together and sort of try to link it to this big picture stuff of why all of this is important for understanding star formation in extreme environments. Okay, so here is a sort of a very brief and observationally driven overview of what the center of the galaxy looks like. So we're going to build up this multi-wavelength picture. So I'm going to start here and you'll see down the bottom there's this bar and that is going to tell you what the wavelength of light is that we're currently looking at. So we're going to start with this all-sky view, this beautiful guy picture in the optical and you're seeing there, of course, this bright banded across the middle is the plane of our galaxy. These dark features are that are nearby by gas clouds and unfortunately in optical wavelengths we can't see the center of the galaxy because of all the dust in the way. So what we're going to do that white box is there showing the inner few hundred parsecs. So we're going to zoom in spatially and we're going to move from the optical into the infrared. So this is now looking, so you see down the bottom right that's going to tell you exactly the wavelengths and above the image tells you what physics, what physical things we're looking at. So this is a spitzer image and in this image here the blue is where I'm telling you what the hot stars are distributed in the inner few hundred parsecs, sorry there's a scale bar on the top left as well. So we're looking at probably a few hundred parsecs around the center. So the blue is the hot stars, the green and red is a mission from very small dust grains that's been excited by the UV radiation from high mass stars and when we can peer through the dust we see some familiar features. So right there in the middle that's the center of the galaxy so there's a supermassive black hole hidden away in there somewhere. What you're actually seeing there is the nuclear cluster surrounding SAJ star. There are some well-known and famous clusters, the arches and green tuplet just to the left on this image. But what you should also see there are these very distinct absorption features and it's these that got me certainly quite a while going out interested in the Atlantic center because this is if you look down at the bottom right this is eight microns is the longest wavelength. So these things are showing up as absorption features at eight microns. So in order to do that the amount of dust the column you have is very large. These must contain a lot of material and in fact some of these clouds are even dark at 70 microns which means they must have visual extinctions of a thousand magnitudes or more. So these are crazy compared to what clouds you would typically see in the disks of galaxies. They're incredibly dense and so I got interested in studying these objects and if instead of looking at infrared so now we're going to go to longer wavelengths and instead of eight microns, 70 microns they're still optically thick. If we go past the peak of the black body we start to see that they glow. So now red here is the emission from the cold dust and you can see that the inner few hundred parsecs is crammed full of very dense molecular clouds shown in here and the blue in this picture sorry so the red is from Herschel and the blue is the emission from hot dust and young stars. So you can also see just it says embedded star formation that there are also some very luminous objects so this down here it says embedded star formation so my pointer isn't working for some reason otherwise I put my mouse over it. So there are also signs of prodigious star formation activity so that's Sagittarius B2 there where it says embedded star formation and that's currently it's basically a mini starburst it's forming it's 10 to the 6 solar masses a gas cloud and forming currently forming stars like crazy in fact half of the star formation current star formation in the galactic center is happening there. We can see even more energetic processes if we now go from the submiliter all the way into the radio so this is now 30 centimeters with with meerkats in red and you start to see supernova remnants popping up and you can peer right in and see all this embedded star formation that's happening around your eyes probably immediately drawn if you haven't seen this image already to these non-thermal radio filaments and if you're particularly good at noticing these sorts of things you might see two vertical again I'm sorry my point is not working two vertical features they're they're broader and we think these this is the base of a very large outflow that's been been driven for the energetic event a few million years ago. So I love this image so much this meerkat image I can't resist showing it in all its detail just to get across the point that there are there's so much activity so many highly energetic processes going off at the same time in here so if you're interested in the high energy universe so to the very right hand side of the scale bar then this is a great place to look I can't just a little plug at this came out the other day this is the new meerkat image and if you have a chance you've got spare 10 minutes I encourage you to have a look because it's the data is just quite quite jaw-dropping the level of detail here is it's quite remarkable. Okay so that was a bit of a whistle whistle stop to a very observational hopefully give you a feel for what what sorts of things are going on in the center of the galaxy but there's two main things really to take from that going forward so number one is that we have a very large reservoir of very dense gas clouds and simultaneously there's a high concentration of energetic phenomena things like supernova young stars forming star clusters and so what we want to now do is to compare those things to other environments and in order to do that we need to go from just this very qualitative picture of yes there's dense gas clouds yes there's supernova and to to measure quantitative values for that so what we're going to do we're going to now try and measure this so how do we do that well this is um my most boring slide I apologize um but it's just to try and get across the point there are many many ways to do this so I think showing a table in a talk is terrible I won't spend too long on it um but I just get across the point that many people have done this um they're using many different methods so typically what you do is you will take your favorite um samples for star formation it could be supernova or or young stellar objects ysos or you might take all the integrated lights and try and understand how much of that's from star formation um and once you've picked your favorite indicator you can estimate a timescale for you know how long does that emission last you can estimate the mass of the object that's producing it you can divide one by the other and you get your star formation rate um so as I say this is a terribly boring boring plot but it's just to get across a point that lots of people have done this and uh the take home message is at the top is that no matter what you do no matter what star formation tracer you pick um you always end up to this the current star formation in this human set is about 0.07 solar masses per year uh that's if you measured in the past a few million years but there is also um some cheeky evidences that there might have been um an elevated star formation rate over the past 30 million years that are the observations we look at so supernova remnants and the young stellar objects might not be sensitive to so there's a paper which suggests that you know evidence for this might be things like the arches and when tubular clusters are very massive uh clusters that formed probably you know in the five to ten million years uh a go range uh so there might be a spike possibly up to 0.8 solar masses per year within the last 30 million years okay so we've got a measure of star formation rate and what we now want to do is to compare that star formation rate with that dense gas reservoir and then compare to other star formation rate in dense gas reservoir dense gas reservoirs across the universe to see if they're similar or not it just so happens that there was a really nice paper did this by charlie ladda back in 2012 so charlie did the hard work here of going through the literature and measuring uh all of the collating dense gas measurements um from all the way from gas clouds on the far bottom left in green are clouds in the milky way then all the way up in mass so sorry masses on dense gas masses is on the x-axis so in log 10 solar masses per year um going from sort of 10 up to 10 to the 10 uh solar masses with a very big dynamic range in mass um so all the way from from galactic clouds clouds nearby earth uh all the way up to high redshift galaxies up in the top right so there's the masses on the x-axis the mass of dense gas on the x-axis and then the y-axis is a measure of the star formation rate and so this is the the plot from charlie's paper and the really nice and exciting thing about this was that everything fit seemed to fit on the same line and that line was linear so everything from milky way clouds all up to high redshift galaxies appeared to fit on this really nice line and the the interpretation of that is that perhaps there's a universal density for star formation now the reason this is so interesting uh if it's right is because that means the kind of implication of that means that if you study the things way down the bottom left of the plot if you can study um nearby star forming regions which of course you can see in so much more detail and you can high redshift galaxies then if you can understand what's going on there that will tell you everything you need to know about these high redshift galaxies so if this is right it's really important so what do we expect the cmsz to be in there our own galaxy well we've already said that all the observational evidence suggests the star formation makes about 0.1 solar mass per year so that's minus one on the y-axis and you can draw your head or on the screen a line across so you'd expect there to be about 10 to the six or 10 to the seven solar masses of dense gas there um but what we in fact find is that there's way more gas than or at least an order magnitude more dense gas so flipping that around another way of putting it is that given the amount of dense gas in there the the center of the galaxies under producing stars by a lot so the this little inset on the top left here is if you take away so everything fits on the slope if you normalize um get rid of that slope and then the blue are showing extra galactic centers and you can see that the the cmsz so that the solid dashed line is that is where everything should line if it was uniform if there was a universal density threshold and the cmsz is at least an order magnitude lower than that so that is intriguing that's the puzzle why is this so different it's annoying because if everything was the same we could understand star formation but it's not it's different some physics is making that gas different okay so as the steam said just weird what about other the center of the galaxies so what you really want to do so if we go back to this plot here you see there's lots of blue or the hexagons so that there's lots of measurements of nearby galaxies but all these galaxies are different they're different masses they're different types um so comparing to the cmsz is not an apples to apples comparison so what you really want to do is find a trend of the Milky Way and it just so happens that um m83 is a nearby galaxy and what i'm showing you here in the left column is the central molecular zone of the Milky Way and the right column is the central molecular zone of m83 so again there's loads of information here it's a boring slide in many ways but the the key thing to take away is that most of the the key physical properties you might care about you know the mass is the the gas content stellar the velocity dispersant the gas electricity all these things are you know very very similar between the two galaxies but notice the star formation rates the cmsz as we said is only 0.07 solar masses per year 0.07 solar mass of pure star formation rate whereas the um incentive m83 is an order magnitude higher as 0.8 solar masses per year so what's going on this is we went looking for for twins of our galaxy but we found a twin that we didn't really expect okay so we've covered a lot of ground here so it's time to kind of stop and reflect where where we've got to and set a stage for for going forward okay so we we said right at the start and we know that star formation and feedback in galaxy centres plays a key role in in shaping the evolution of galaxy populations so if there is an environmental change in star formation it's crucial we understand why we've just seen certainly that the research over the past five ten years it has shown that the cmsz is underproducing stars by one to two hours of magnitude given how much dense gas it contains so what's going on well we've basically got one of two possible scenarios here two potential explanations either the the star formation in a central micro zone is currently at a low point in the star formation history and then will will rise again at some point or there's something that's actively inhibiting star formation at the centre of the galaxy and you might say well yeah so what you know who who cares what why do we even care about this well we should care and the reason is because the extent to which feedback changes a galaxy depends really sensitively on the the spatial and temporal distribution of that feedback and a very simple analogy or way in this context so we say the star formation rate is currently 0.07 solar masses per year and let's imagine that we just let the the cmsz trundle along at that rate for the next 20 million years and then we should observe it in 20 million years now instead of that imagine we take that same integrated star formation but we cram it down into a two million year window in a very small spatial region the galaxy is going to look completely different so the first scenario there's no way that could ever drive anything like the firmy bubble it's just not enough accumulated energy all the energy will the of the star formation supernova will will dissipate and cool before it can do anything on a galactic scale whereas the latter scenario is going to cause serious damage drive large-scale outflows and so on so we should really care and strongly and if we're interested in looking at these phenomena with high energy telescopes like cta it's really important that we understand which of these two scenarios we're talking about okay so what are some potential solutions to this puzzle okay so um we've got these two scenarios and uh through i guess in investigations of last few years we narrowed it down there's two plausible physical mechanisms that can be responsible for this so if the case is that we're presently observing star formation in a kind of a low state and it's going to go back up again then the obvious physical mechanism for for doing that is is large-scale process so galactic scale processes and are driving this spatial and temporal variation in star formation whereas if if this is you know if the star formation is low and it remains low over long periods then there has to be something that's locally um causing star formation to be different to be suppressed for a given amount of dense gas in the center of the galaxy so these are the two things that we we want to investigate and we want to understand if that's true what could be causing this okay so let's go i'm going to go through each of those in turn so let's um first of all could it be galactic scale processes well to see if galactic scale processes are are responsible we need to understand what we think drives in the first place so uh a good a good place to start is why why do we have a cmz at all in the first place not all galaxies do um so what what you're seeing here this is a um a top-down view of what we an artist's impression of what we think our galaxy might look like and probably the the key factor in all this your eyes already been drawn to and that's the fact that we have a bar we have a stellar bar like two-thirds of all spiral galaxies in the local universe we have a stellar bar and that stellar bar doesn't ask these stuff to the the gas in the disk so the stellar bar is rotating and as it rotates the gas and disk uh near the the the end of the bar fuels a torque and because gas is dissipationally can shock it can lose energy it can lose momentum and then it can plunge in along the leading edge of the bar into the center so we've got a good idea of what's going on here so there's great work by um so some simulations here by Matteo Sormani uh Robin Tress and Rav Klesson their their group uh showing how this works in practice so they've taken the simulation of a milky way like galaxy they've put in a milky way like bar uh and you can see so the different panels it's the same simulation they've just done different processing so the top left is the total gas then stepping through you see the atomic gas then molecular gas and going down you see the CO so that's what we'd actually observe carbon monoxide mission there and on this or bottom left image of the simulation is the star formation uh going on so we have a good understanding if we know what the potential the gravitational potential of the bar is we've got fair idea of what um of what's happening and it's basically these the gas comes in in what we see in external galaxy or dust lanes now the important point is that the gas um because of the gravitational potential the gas build up you can see these um these rings uh so I was saying that I mentioned it's unstable are you are you still can people still hear me can someone just say hi yeah yeah okay fine right yes thank you thanks um yeah so so the gas so the one particularly important thing to notice is that so the gas is funneled in but you see that there's these these this ring that builds up and that's because of the stellar the stellar potential which is dominant in so far in towards the galactic center um basically sets up a stalling point where the gas builds up in in a ring so that's what we we observe that is the the central molecular zone that we're talking about the inner few hundred parsecs where this gas piles up on a ring now we're interested in this question is star formation static is it quasi continuous or is it bursty so well hopefully simulations would give us the answer right well uh unfortunately there are two different different answers there so I'm showing you here that are star formation so simulations of a disc like the milky way with a bar and following the gas in and asking the question is star formation bursty or or quasi continuous so the one on the left this is by Lucia Armolotta I'm showing some results from from her simulations where you've got the so star formation rate is on the the y axis on the top plot and then the time in in mega years and so in her simulations she finds that star formation is is very bursty so the that sort of orange horizontal stripe is the the current estimate of the the cmz our own um galaxy's star formation rate of sort of 0.1 solar masses per year and so her simulations do get down there but it's it's a kind of low point and then there's like a burst of star formation so that's these simulations are very bursty so on the right hand side these are our simulations by Amityus or Manny and they find something different in their simulations again global global simulations gas falling in um their their star formation rates are much more more continuous so uh I think the certainly on the simulation side that this is still an open question okay so let's look at it from um so simulations you know we're working working this out what about from the observational perspective well we can try and tackle this by asking what happens to gas when it enters the essentially the zone and we can we can do that in a very simple mass budget so you can see right we know gas is getting funneled in we know it builds up in this ring and so we can just ask how much is coming in how much is going out how much is going into stars am I doing this kind of mass budget we can estimate is it likely you know do all those masses cancel out in other words are we in a quasi continuous thing or does it look like there's a sort of a mismatch um between the mass coming in and mass coming out and maybe that's some indication that we were having more star formation diversity okay so this is um I'm sure you hear this is a very simple uh attempt to do that so on the left hand side we've got m dot in which is the sort of mass inflow rate coming along these dust lanes into the center and SFR that's the the current star formation rate m dot out is the the rate at which gas is being blown out of the cmz and then the m dot cmz is the the the change in mass of the stars in so it's a change in mass of the gas in the cmz okay so we've already said let's look at these terms we've already said the star formation rate's about 0.1 solar mass per year currently um we can measure uh the mass inflow rate is about one solar mass per year this is a paper by uh Matias O'Malley and and Ash Barnes where they they picked out this figure just beneath that is showing um the the CO position velocity diagram and you can pick out the dust lanes that's what's shown in the blue and orange you can measure uh the the mass of the CO in those two two components and then if you've got a model of a galaxy you can get a rate at which it comes in and there the number is about one solar mass per year so the rate at which gas is being expelled is about 0.6 solar masses and here's uh you know I just I'm blown away by this just that this year scale of this but it's clear that the large amount of mass is being blown from the cmz zone I like doing this as an observer is that I can tell that the right hand side must be building up so in order for this to to match one solar mass per year then the amount of gas that's in the cmz must be must be growing if those other numbers are right so this may be observational again this is so very hand wavy and there's quite a bit of uncertainty in these numbers but this is potentially observational evidence that that the star formation is bursty in um the the cmz okay so it certainly says so going back to our our original you know too pronged idea or two two different mechanisms certainly seems that variations on on large sort of kiloparsec galactic scales may play a role in the reason why the star formation rate seems low at the moment um so what about this other idea of kind of more local processes somehow keeping star formation very low over a long time so well before we we get there what do we mean by extreme we need to quantify that before we can understand what physical mechanisms might cause it to be extreme so here we go this is the same top-down view of the galaxy and one thing that we can say about um the star formation in the center of the the gas in the center is that it's really very dense so just to give you an idea of flavor for that so the inner say a few hundred parsec it contains between three and ten percent of all the molecular gas in the galaxy and yet the surface area is point one percent so that tells you immediately just those two numbers that compared to the gas in the rest of the disk this gas is super dense so that's number one so that could be um these but then that would be strange because all all star formation models think that as you increase the density of the gas then your star formation should go up so this is one thing that's different but it's different in the wrong way completely the wrong way so what might be stopping it well another thing that we know about the said the gas in the center of the galaxy is it's incredibly turbulent so what does that mean that means that there is a lot of the for a given fixed size scale if you take a molecular cloud in the disk and a molecular cloud in the galactic center and you have to measure how much kinetic energy there is in the gas on the same size scale in both there's way more kinetic energy in the galactic center clouds and that's what's shown here this is a typical line width size relationship for for clouds so the x-axis is you go around and you measure clouds in the disk and clouds in the center and you plot their size that should be in par six on the x-axis and then in the y-axis you measure on that same size scale you observe something like CO and you measure the velocity dispersion of that line and so you have a size and you have a line with them you plot them and so you can see the the yellow are the cmz clouds and for a fixed size scale if you go up in you take a fixed size scale next axis and you go up in the y-axis you see that the cmz clouds are can be 10 times greater the velocity dispersion that means there's a lot more kinetic energy in the gas so that clearly is an important consideration when you're thinking about star formation and star formation is basically self-gravity of the gas fighting against things like kinetic energy and so on there's trying to stop eclipsing so that's obviously important and indeed so that's so the gas is denser it's more turbulent and in fact we can expand that for pretty much any property you know turbulence but also magnetic fields gas temperatures density pressure cosmic realisation rates all these things are an order of magnitude or more greater in the gladiator center than solenoid so pretty what means by extreme we say you take any measure um any physical property and it will be at least an order of magnitude larger in the cladding center and you'd think surely that's got to play some role in affecting the star formation and also the feedback as well so when stars do form and the feedback goes off I must play a role okay so um this is a very visual again another thing that when I started looking at the gladiator center kind of blew my mind um and let me show you that and I still I still find it quite amazing so what I want to do is when we say dense extreme how dense is dense so this let's look at this little cloud here's one of my my favorite objects are called the Colbert brick and this is one of the sort of densest and most massive molecular clouds in the galaxy that doesn't have any signs of of star formation so that's what's shown here this is uh the the red is a Herschel and then this beautiful uh yellow orange image here this is an Alma showing individual star forming cores in this this gas cloud so that just looks you know it's easy to to take that for granted but it only the the scale of how extreme this is only becomes important when we compare that to something in the disk so now what I've done here is I've taken that gas cloud and I've compared it in size to the Orion like a cloud now Orion is our um local um extreme star formation environment it's the nearest place in the galaxy where we're forming high mass stars and it's often looked to as you know our our nearest extreme example of star formation so actually what has happened this is showing so you see the the Orion filament here and that's about 10 to the 5 solar masses of gas and that's forming stars like crazy what the universe has somehow managed to do is to cram all of that gas so that tiny little gas cloud there is the same amount of gas as in the whole Orion cloud it's managed to compress all of that down to a radius of a few par six and stop it forming stars so that that to be that that is extreme how the the sort of physical question we're entering is what what can stop the this gas cloud from forming stars as you compress it to such a degree so we have a fair idea of what might be causing that it's a combination of of different things obviously increase in magnetic magnetic fields the huge amounts of of kinetic energy in that gas and the gas is effectively being pushed to very very high densities by things like the external pressure and by the the strong surrounding gravitational field and a lot of the gas is dense but it's not self-gravitating so there's a figure is trying to show that here so what there's a paper we published a few years ago we take this spectacular almond image of this gas cloud and we ask the question well what does this what's this density distribution look like so we've got this the the image here in orange on the left what we've done is we've done a probability density function of the column density so on the x-axis is basically the the density of the cloud and on the the y-axis is basically the number of pixels at that density so you can see this is makes a really sort of nice log normal shape and that's what you get predicted by if the gases is very turbulent I can explain why that is if if anyone's interested but the key point here is that vertical dotted line here this is that universal density threshold so remember the the the ladder plot I showed where everything was lying on this nice line the the prediction here is that at a density of about 10 to the 4 particles per centimeter cubed everything begins forming stars and what was clear from this almond map is that pretty much all of this gas cloud is above that density and yet virtually none of it's forming stars the only bit that's forming stars is this tiny little bit that's just off that log normal at the very high density and there's one little clump in here that we now know this is another beautiful almond image that made by Dan Walker this is now one sort of thousand day use scales where we can see these are little protosteller outflows coming from from stars right within there but most of this cloud is doing dilly squat it's above this density and it's doing nothing so that can't be so it cannot be a universal density threshold there has to be additional physics that's stopping this cloud forming stars and so there's been lots of work on this and this is just calculations if people are interested the take home message is that the local environment is really important it really matters on these small scales if you have a lot of excess velocity emotions whether that you know the kinetic energy in the gas that can be from injected from shear it can be for whatever reason if you have strong magnetic fields all of these things mean that star formation is strongly environmentally dependent this this just right what I'm showing you here fundamentally rules out star formation being environmentally independent just it can't happen so we know that star formation must be environmentally dependent the question is what is the key physics that's driving that okay so we had these two potential explanations and unfortunately as always seems to be the case that it looks like probably both of them play a role both galactic scale processes the things that drive the gas in and shape the big picture shape the sort of big scale gas motions but also what's happening right down on the size scales of individual forming stars both of these things and in fact it's probably the case that they completely interact with each other and it's you know it's a sort of oh where are we how do we make progress on this well that's where we get to aces so aces the the ALMA CMZ exploration survey and its goal is to do exactly that so aces is going to drive the the the properties of all of this star forming gas all the way from 100 parsec scales all the way down to individual forming star scales and it's going to measure the the the gas the young stars and everything in between from all these different scales so I'm going to spend the last probably two minutes just giving you a very quick lot something meter expert so there's a whole lot of information these sites I can come back to if people are interested in but I just want to really spend time on one key figure and that's this figure here so what we're showing you here is lots of different colors I like to draw your attention to everything except the red so the red is aces that everything except the red is what was there before so the galactic center is one of the most highly studied regions in the sky and there have been lots of pencil beam studies of this object and that object and we've learned a lot about star formation but the thing that's been missing is we have had no way it's been completely each object is a little isolated island so if you look at the blue and the orange there these little pencil beams and we've not been able to link that to the the big scales that we now know are crucial in setting the small scale scale properties and again it's the small scale properties to then feedback so aces what one of the the real step changes is that the red outlines this is the inner 200 parsecs aces is going to map the whole thing all of this red all of that dense class all of the dense gas clouds all of where we saw those supernova remnants and the young stellar objects and the very center all of it from 200 parsec scales all the way down so it's down to one mark 0.05 parsecs and a whole bunch of different lines and we'll measure all of the you know have a complete census of everything down to 0.2 kilometers second resolution so that's about the the thermal about the thermal lines so yeah there's I'm going to skip over there's a whole bunch of please a whole bunch of information on this you know what lines we're looking at what sensitivities are you know what the structure the project is and our key sort of science goals I'm happy to come back to that I'm not really sure what people are interested in so I've got lots of information there but it's very easy to join if you're interested it's just the case of you know contacting myself for one of the other co-pias and filling out a Google forum and you know we'd love to have you have you join you know just even a discussion if you don't want to join this discussion how can we make this data available most useful for the high energy community that would be absolutely fantastic so please do do that right that is so I just thought there was a question in the chat I'll come back to that oh dear I can't sorry I've lost my cursor not probably in the SIVA I can read it so there was a question from could you hear me SIVA okay yes so there was a question at late so I've got one more slide should I just finish with my my last slide okay if I can move it so I'm having I don't know if you can hear that my thing seems to be frozen so I'm going to stop sharing now there we go okay so finally sorry about that little technical hitch so final slide what role can studies of the CMZ play well right at the start we're seeing the the the CMZ is the nearest environment that we can simultaneously observe many of the extreme processes that shape universe but it's our you know understanding the star formation feedback is currently limited by the lack of this kind of unified framework from linking from from the 100 parsec scales down to individual star formation and feedback points and ACES will sort of bridge that gap and it's open to the community so if you're interested please let me know and that is my final slide