Don't Judge A Galaxy By Its Cover

As discussed in previous posts (e.g. here and here), the morphology of a galaxy is a powerful tool when it comes to understanding galaxy evolution. The Hubble Tuning fork diagram, first devised by Edwin Hubble in 1925, shows that galaxies have three different types of visual morphologies: spheroidal (or elliptical), disky (or spiral), and peculiar (or irregular).

The Hubble tuning fork diagram. On the left are spheroidal galaxies, also known as elliptical galaxies. The number which follows the 'E' tell us if the galaxy is circular or flattened. On the right of the diagram are disk galaxies, often called spiral galaxies due to their spiral arm features. The 'B' in the notation for spiral galaxies tell us whether or not a bar feature is present, and the lower case letter tells us how tightly wound the arms of the galaxy are. The final galaxy on the far right is an example of a peculiar or irregular galaxy. 

On the left hand side of the Hubble tuning fork above are the spheroidal galaxies and the disky type galaxies are on the right. An example of a peculiar galaxy is shown on the far right. Not only does this image show us the different types of galaxies, it also shows us clearly that galaxies of different types have different colours. The spheroidal type galaxies are redder, while the disk and peculiar galaxies are blue in colour. If a galaxy is blue it is still young and making new stars. If a galaxy is red it is older and no longer has the fuel to make stars.

Rather helpfully, colour is not the only property that correlates with galaxy morphology. Galaxies that have a greater stellar mass tend to be spheroidal, while the lower mass galaxies have disk and peculiar morphologies. The massive, red, and old spheroidal galaxies are usually found in denser environments than disk and peculiar galaxies. Also, galaxy morphology is often measured using different parameters determined computationally, which in turn relate to the visual morphology of the galaxy.

Galaxies of different visual morphologies. Many of the important features which
allow us to tell these different types of galaxies apart have been revealed
to us thanks to the fantastic CANDELS imaging.

So does this mean that by simply looking at the shape of a galaxy you can tell all these different properties? The answer is not so straight forward. Many of the relations discussed above are what we know to be true in the local Universe, that is to say, they are true for galaxies close to us. As we begin to look at galaxies further away, we are looking at earlier epochs in the life time of the Universe. These galaxies are said to be at higher redshift than their local counterparts and may not have the same properties as those found close to us. Local galaxies have had the entire age of the Universe to form, whereas distant galaxies are younger and therefore are at an earlier stage of formation. Unfortunately, as a galaxy gets further from us, we need increasingly good telescopes to clearly see the visual morphology of a galaxy. A particularly difficult question to answer about distant galaxies has been 'What are the visual morphologies of these galaxies and how do they compare to the Hubble tuning fork?' Now, thanks to the high resolution CANDELS imaging, we can take a look at these distant galaxies and find out about their visual morphologies.

The fraction of galaxies with spheroidal (red), disk (blue) and peculiar (black) morphology as a
function of redshift. As redshift increases the distance away from us increases and the age
of the Universe decreases. This plot shows how the fraction of galaxies changes from
when the Universe was ~6 billion years old to when  the Universe was only 2 billion years old.

We can see from looking at these fractions that as we go further and further out, and the Universe gets younger and younger, the number of galaxies that don't fall nicely into the Hubble tuning fork scheme (the black line) begins to increase. This tells us that at earlier cosmic times the Universe was a messier place than it is today, and that galaxies are busy forming at these times. One puzzling result from this plot is that galaxies which look like Hubble type disk galaxies (the blue line) seem non-existent when the Universe was younger. Other CANDELS work, which has looked at the morphology of galaxies determined by other parameters (e.g. here), have shown some distant galaxies do have properties similar to the disk population in the local Universe. This seems to be telling us there are no galaxies with visual disk morphologies but galaxies which do have similar properties to disks. We can explain this when we consider results from other studies which show that disks in the distant Universe have clumpy structures. These clumps could cause the galaxy to be classed as a peculiar galaxy even though the underlying galaxy structure is that of a disk. In fact, studies have shown, through a process called Integral field spectroscopy (IFS), that such systems do exist. See this publication for a discussion of how IFS has been used to look at the underlying structure of a galaxy.

The results discussed here are important when considering the visual morphology of galaxies. It could be that disk galaxies in the early Universe are simply ‘hiding’ from us because they have different visual morphologies when compared to classic disks from the Hubble tuning fork. This is telling us that judging a distant galaxy based on our ideas regarding visual morphology in the local Universe may not be the best approach. Fortunately the CANDELS dataset has imaging available which is even deeper than what is used in this study, and will have visual classifications for many of these galaxies. These visual classifications come from projects such as Galaxy Zoo and the CANDELS team wide effort to visually classify all the CANDELS galaxies (this will be discussed in a future post). Data from CANDELS will play a key role in the continuing to investigate what visual morphology really means when looking at distant galaxies.

Not a derby but the CANDELS 2013 team meeting

As we have for the last few years, the CANDELS team members come together to present the fruits of their labor over the last year to the rest of the team and discuss and make new plans for the coming year. This year, we're meeting at the University of Kentucky in Lexington.

Those of you who are following us on Twitter (@CANDELS_team and #CANDELS2013) might already have a pretty good idea on what yesterday was all about. If you didn't, let me give you a short description on what we did yesterday and you still have the chance all week to follow our live tweets.

Yesterday was all about giving status updates to the team, from the PI's, the data reduction and observation schedulers, most of the working group leaders and quick lightning talks from each member on their current CANDELS project. This is not only useful for long-term team members but also offers all the newly joined students and postdocs who participate in their first team meeting to get a quick update on available data, catalogues and on-going science projects.

After the first welcome and general logistics (and breakfast of course!), Harry Ferguson and Sandy Faber - the two PI's of the CANDELS survey - summarized the team's scientific accomplishments of the past year, listed their goals for the meeting as well as big science questions to address in the future. We learned for example that in the last three years, the CANDELS team published on average one paper every two weeks. That's pretty impressive and amounts to quite a number of publications. Many of which team members have already posted here about.

Poster advertising Sandra Faber's public talk at the University of Kentucky
Image credit: University of Kentucky, Dale Kocevski

With regard to observations and data reduction, this team meeting happens at a very special time. As Harry Ferguson already told you in this post, all planned observations for CANDELS are now completed. We have all the data! 

Then we moved on to the lightning talk round. A lightning talk round is exactly what it sounds like, it's over in a flash of a second. Everybody (about 50 meeting participants) had the chance to summarize their current CANDELS science projects in one slide and maximally two minutes. With all the different projects on-going, that is quite a tough job. But I thought everybody managed well and I'm looking forward to hearing more details in the science talks scheduled throughout the week as well as talking to people during the week about their projects.

Finally, most working group leaders gave short presentations highlighting some of the science results achieved within the working group in the past year. They also provided an overview over what data products and catalogues, like the redshift catalogues or multi-wavelength catalogues, are available for the team to use and where to find them. We heard updates from the Spectroscopy, High-Redshift, Extragalactic Background Light, Multi-wavelength catalogues, Clustering and Environment, AGN, Theory and the Education and Public Outreach working groups. Of course the blog was featured in my summary of the CANDELS outreach efforts. The day finished with a few theory-related science talks.

Tomorrow, the day will be structured differently. We will listen to more science presentations from team members and in the afternoon we will split into sub-groups to discuss current as well as future projects and "work to be done" in the working group sessions. And if you find yourself in Lexington, don't miss your chance to listen to Sandy Faber's public talk on "Modern Genesis: The Amazing Story of Our Cosmic Origins" at 7pm!

Making Statistical Inferences with Images: Using CANDELS Data to Learn About Our Universe

The data from the CANDELS program have been, unquestionably, a boon for astronomers, providing them with an unprecedented means by which to view galaxy evolution in the early Universe. But these data are a boon for statisticians as well. That's because of their complexity: going from, say, images to making inferences about the Universe requires the use of statistical techniques that can be considerably more advanced than simple linear regression. (And it may require new advanced techniques as well.) The application of the newest, most cutting-edge statistical techniques to CANDELS data: this is where I and my collaborators come in.

I am part of a small but growing class of astrostatisticians. We work at the boundary between astronomy and statistics, understanding the data and the science of the former, and applying the latest methods of the latter.  For my part, my Ph.D. is in astronomy, but for the last decade I have worked in Carnegie Mellon's Department of Statistics and with the International Computational Astrostatistics (or InCA) group, a collection of CMU statisticians and computer scientists as well as astronomers at CMU, Pitt, and places beyond. I work to facilitate communication between statisticians and their astronomical counterparts and, to borrow a phrase from computer science, I try to "abstract away" the complexity of astronomical data to make them more immediately accessible to statisticians, particularly to statistics students.

One major aspect of an astrostatistician's work is working with experts to internalize the nitty-gritty details of the science underlying a particular dataset. But another involves looking beyond these details towards the "big picture."  Are there newer and better ways to analyze a particular dataset, or to answer a particular scientific question? For the specific case of CANDELS, thinking about the big picture has led me to ask the following question: how exactly should we turn galaxy images into constraints on parameter values for cosmological and astrophysical models? Below, I'll describe how one might do this...and long story short: it won't be as easy as performing simple linear regression.

An illustration of the question posed in the text above: how do we turn galaxy images (in this case, the four representative H-band images of high-redshift galaxies from the CANDELS program shown at left) into constraints on parameter values for cosmological and astrophysical models (in this case, the 68- and 95-percent confidence regions for the values of two cosmological parameters shown at right)?  The pixels for each of the galaxies at left are colored according to relative intensity: for instance, we observe less light in a pixel colored green than we do in one colored pink, or red.  Yellow-colored pixels are associated with maximum galaxy intensity.  One might wonder about the two galaxies at left, where the yellow pixels appear offset from the image centers.  These are examples of disturbed galaxies, which are relatively common in the chaotic universe of 10 billion years ago: what we see as a single "galaxy" actually might be two galaxies that are completing the process of merging together.

The basic recipe for constraining the parameters of a given model (like the Lambda CDM model) should be familiar to anyone who has ever tried to fit a curve to a set of data: assume parameter values (like the slope and intercept of a line), construct predicted data based on these values (determine the amplitude of the line at each observed datum), numerically evaluate the difference between predicted and observed data (such as by computing the squares of the differences), and iterate, changing the parameter values until the difference metric is minimized. This recipe seems clear and easy to follow...but with CANDELS data the devil will be in the details!

The first devil-infused detail is "constructing predicted data." Our predicted data are galaxy images, and to map a set of parameter values to images we need state-of-the-art simulation software that takes into account all the intricacies of the physics involved in galaxy formation. This is a detail I leave to the experts; it suffices to say here that members of the CANDELS team including Joel Primack, Avishai Dekel, and others are on the case, combining cosmological simulations with code that models how stars evolve and how photons diffuse through dusty environments to create lovely images of galaxies. So while there is presumably still much to do to  perfect the simulation models, the construction of predicted data is not something that we should have to worry too much about in the long term.

The second devil-infused detail, "numerically evaluating the difference between predicted and observed data," is more problematic. How exactly does one compare (up to hundreds of thousands of) simulated and observed images? A direct image-by-image and pixel-by-pixel comparison is not appropriate, because of the random nature of simulations: we cannot expect a simulation to reproduce the structural details of galaxies that exhibit bars, arms, and/or clumps of star formation. Instead, what we want to do is to compare the entire ensemble of simulated images with that of observed images.  For instance, suppose that each galaxy image is a "postage stamp" measuring 100 by 100 pixels. One can use each of these pixels to define an axis, creating a 10,000-dimensional space; a given galaxy's value along the first axis would be, for instance, the intensity in the lower-leftmost pixel, while the galaxy's value along the second axis would be the intensity in an adjoining pixel, etc., etc. Once all the galaxy images are mapped to this space, we'd have two sets of points, for simulated and observed galaxies, respectively. Then all we have to do it compare them: how "far" is one set from the other? Eventually, we'd want to find the set of model parameters that minimizes that distance.

Before answering that, we should probably admit that working in a 10,000-dimensional space is actually infeasible: we would suffer from the so-called "curse of dimensionality," wherein the amount of data needed to achieve a precise statistical result generally grows exponentially with dimension. But all is not lost, because we wouldn't want to work in such a large space anyway, if we can avoid it.  We expect that galaxies "live" in some subset of that space, perhaps one of much lower dimensionality. For instance, all the galaxies might inhabit a line or curve running through our large space, or perhaps a plane. We don't expect the space in which the data live to be quite so low dimensional, but it may not be much more complicated than that.

The "noisy spiral": these data live along a
one-dimensional spiral embedded in a
two-dimensional space, much like we expect
galaxies to inhabit a low-dimensional subset
of the high-dimensional space defined by
image pixels.  From Lafon & Lee (2006).

There are various flavors of "dimension reduction" techniques that we astrostatisticians use frequently. Some are relatively familiar to astronomers, like principal components analysis, and others less so. Here we'll concentrate on one familiar to galaxy morphologists: using summary statistics. A summary statistic is simply a mapping from data values to a number, with the most familiar one being the mean, or average, of all the values in a dataset. A number of statistics have been developed for summarizing galaxy images in a way that retains important morphological information. (For instance, in Freeman et al.  (2013), we propose three new summary statistics that are useful for detecting disturbed morphologies, which the reader can think of as separating those galaxies with clumpy profiles from those that appear smooth.)

So, let's assume that we have summarized all of our simulated and observed images with some number of these oft-used statistics. Now, instead of two sets of points in a 10,000-dimensional space, we might have two sets in, e.g., an eight-dimensional space. That's more like it...but what do we do now?

One answer to this question involves the statistical concept of density. A probability density function, or pdf, is the probability of sampling a datum, per unit (multi-dimensional) volume. For instance, there is a pdf from which human heights are sampled: we can compute the probability of sampling a height between 66 and 68 inches by integrating this pdf over the range (66,68), and we would find that that probability is much larger than the probability of sampling a height, for instance, between 80 and 82 inches. To compare our sets of points, we could estimate the pdfs for each, then compute some metric that encapsulates how different the two pdfs are. Or even simpler, we could utilize work by my colleagues Ann Lee and Rafael Izbicki and base our metric on the ratio of pdfs at each cluster point, which can be estimated simply without knowing the pdfs themselves. We don't know yet what the optimal method will be, both statistically and in terms of computational feasibility. It's an open question, which is the kind of question statistics researchers like best!

So check back in a few years: maybe by then our group here at CMU, or some other group, will have solved the problem of making statistical inferences in an effective manner using galaxy images. Hopefully it will happen, and if it does, don't worry that astrostatisticians like me will be left with nothing to do. The great thing about astronomy is that there shiny objects everywhere that can grab an astrostatistician's attention. There will always be more data to analyze, and with these data there will always be more statistical problems to solve.

Astronomer of the Month: Karina Caputi

Each month we will highlight a member of the CANDELS team by presenting an interview introducing them and what it's like to be an astronomer. This month's Astronomer is Karina Caputi.

Tell us a little about yourself!

My name is Karina Caputi and I'm an Assistant Professor of Astronomy at the Kapteyn Astronomical Institute, University of Groningen, in the Netherlands, since 2012. I'm originally from Argentina, and Iived there until I permanently moved to Europe in 2001. 
I studied Physics at the Instituto Balseiro,  in 
the beautiful town of Bariloche, in the Argentinian Patagonia, and then I did a PhD in Astronomy at the University of Edinburgh in the UK. After my PhD, I worked in different parts of Europe: the Institut d'Astrophysique Spatiale, in Orsay, France, the ETH Zurich in Switzerland, and I have been back in Edinburgh for some time. Finally, I have settled in the Netherlands with a faculty position.

In my spare time I like traveling (more than what I usually do for work!), reading fiction, listening to music, cooking, and shopping -- I love buying clothes and perfumes! I'm not a very sporty person, but I do enjoy jogging outdoors when the weather is not too bad.

What is your specific area of research? What is your role within the CANDELS team? 

I'm an extragalactic Astronomer, mainly focused on infrared galaxy surveys. I study galaxies at high redshift, which are so distant that the light we receive from them today was emitted when the Universe was less than half of its present age. Working in the infrared allows me to select galaxies whose star formation and/or black-hole activity was hidden by dust, an effect that was very common when the Universe was that young. The UV photons produced by this activity heat the galaxy dust, making it emit at infrared wavelengths. And, apart from the dust emission, the light produced by the oldest stars in high redshift galaxies also arrives to us redshifted into the infrared regime, so studying infrared astronomical images is a very powerful tool to search for all kinds of galaxies in the distant Universe!

My role within CANDELS is mainly searching for galaxies that are counterparts to those appearing in the infrared images provided by the Spitzer Space Telescope. In a previous post, in particular I referred to a special kind of galaxy that is very bright in the Spitzer images but much fainter in the CANDELS HST images. These objects are extreme cases of distant, dust-obscured galaxies, and suggest that future infrared images -- to be taken, for example, with the James Webb Space Telescope -- will reveal many new galaxies that we cannot see with the HST.

What made you want to become an astronomer? At what age did you know you were interested in astronomy? 

As a child, I was always very curious about how different things work. By the time I started secondary school, at age 13, I already knew that I wanted to be a physicist. In parallel, I developed my love for Astronomy, which is where different areas of Physics can be seen 'in action'. The book and TV series COSMOS by Carl Sagan had a tremendous influence on me as a child -- being an Astronomer just appeared as something fascinating. I definitely recognize myself as a product of the 'COSMOS generation'. In the end, I decided that getting a solid Physics basis was the best thing to do first, so I did a Bachelor's and Master's degree in Physics (with no Astronomy at all) and only turned into professional Astronomy for my PhD. It took a bit of extra effort to gain the Astronomy specific background at the PhD stage, but I'm very happy to have followed that path.

What obstacles have you encountered on your path to becoming an astronomer and how did you overcome them? 

Coming from a developing country, making a career in top European Universities required hard work. But fortunately my education was quite strong, as Argentinian universities, and particularly the Instituto Balseiro, offer high-quality education, as virtually all scientists there have spent at least a few years working in Europe or the US.

I recognise that it also takes a bit more effort to make a name for yourself in science when you are a woman, as there is still some unconscious reluctance to believe that women, especially when they are young, can be as hard-working and ambitious as men. But that improves with time, so it's just a matter of being perseverant and self-confident.

Who has been your biggest scientific role model and why? 

I admire many scientists, but I wouldn't call them a 'role model', as I don't think that I've been looking for an example to imitate. As I said before, Carl Sagan has been very influential to me as a child, because he was a great scientific communicator, and made me realise that being an Astronomer was really cool. And of course, I owe a lot to my teachers and supervisors, as all of them have contributed to different extents to make the scientist that I am today.

What is it like to be an astronomer? What is your favorite aspect? 

The constant challenge: you can spend several days not understanding something, but when you do, there is a great feeling of accomplishment. And the fact that you never get bored: once you have answered a question you will have in mind several more.

What motivates you in your research? 

Never-ending curiosity.

What is your favorite astronomical facility? (This could include telescopes or super computers, for example) 

The Spitzer Space Telescope has been my favorite facility so far, as it has widely opened up the possibility of studying the infrared Universe at high redshifts. And I'm definitely looking forward to the James Webb Space Telescope, because it will have the same great potential for discovery as HST and Spitzer together.

Where do you see yourself in the future? What are your career aspirations? 

Discovering new galaxies and studying in detail the physics of high-redshift galaxies, all of which will hopefully be possible with future telescopes. And continuing to form new generations of astronomers - introducing them to the fascinating study of the high-redshift Universe.
 

If you could have any astronomy related wish, what would it be? 

I would like to have an interferometer as powerful as the full ALMA array, but in space.

What is your favorite, most mind-boggling astronomy fact? 

The fact that the speed of light is finite, and thus we can reconstruct the Universe's past by looking at distant galaxies. We have a natural time machine and this to me is absolutely mind-boggling.

Is there anything else you would like for the public to know about you or astronomy in general? 

Just for them note that becoming a professional astronomer is great, but is by no means a simple path -- there are long working hours, jobs are highly competitive, and thus one cannot always choose where to work and live. Having a good degree of flexibility and family support are quite essential. Many undergraduate students of Astronomy are unaware of these facts. But for those who have enough courage and perseverance, astronomy can be a wonderful life adventure.

Were Galaxies Really Mature 11 Billion Years Ago?

Nostra Culpa

Yesterday, the European Space Agency put out a press release on CANDELS research that has been widely covered by various media. Sometimes the scientific message gets garbled in press releases, in spite of best intentions all around. In this case, the wording of the press release is pretty good about conveying the key message (although some of the subtleties get lost). But the gorgeous picture that accompanies the release is more wrong than right. Alas, there was a bit more "artistic license" taken with the press-release artwork than there should have been, and we failed to put the brakes on before the press release went out. The pictures of the galaxies marked as "11 billion years" were not taken from the CANDELS images, and are not at the right redshift (redshift z=2.5 corresponds to a lookback time of 11 billion years). If you would like to see what the images really look like, read on.

This is the gorgeous image that accompanied the ESA CANDELS press release. If only it were closer to the truth! The images further down in this blog post show what galaxies 11 billion years ago really look like in the CANDELS images.

What did galaxies look like 11 billion years ago?

Cutouts from Lee et al.
Galaxies on the right are
forming stars rapidly.
Galaxies on the left are
not. 

The basic conclusion of the papers on which this story was based is that we can start to see the dichotomy between star-forming galaxies being "disk like" and non-star-forming galaxies being "spheroid like" already being set into place 11 billion years ago. That's the central message and is what we are finding in the CANDELS survey in the various samples studied by Tao Wang, Eric Bell, BoMee Lee, Alice Mortlock, Victoria Bruce and others.

We wish we could see galaxies 11 billion years ago with the sort of clarity shown on the press-release image, but unfortunately even with Hubble we can't see that level of detail. To the extent that we can distinguish detail they look (a) smaller and (b) generally bluer, and (c) less well-ordered than present-day galaxies.

So -- yes we can see spheroids and disks emerging as separate sequences -- but it is not the case that the galaxies look like their present-day counterparts, which is the impression that you get from looking at the press-release image.  Arjen van der Wel's quote in the press release that they look "remarkably mature" is reasonable when you consider that they might have all looked like train-wreck mergers-in-process.  But some of the news stories based on the press release are taking that to mean they are completely mature, which is certainly not the case.

Illustration of the morphologies of massive galaxies at redshift z~2 using CANDELS cutouts from Wang et al. (2012). The upper-left insert color codes galaxies on the same axis scale, with blue being the star-forming galaxies and red being the less-star-forming galaxies. You can easily see that the less-star-forming ones tend to look more spheroidal.

The light reaching us from galaxies at a redshift z=2.5 took about 11 billion years to get here. So we are looking back in time to when the universe was only about 2.7 billion years old. Below and to the right are some figures from some recent papers by CANDELS and other teams that show images of galaxies at about this redshift. Perhaps this gives a more accurate impression of what we can say and can't say about the comparison between nearby galaxies and their distant progenitors.

A montage of "Milky-Way progenitor" candidates from the CANDELS images put together by Pieter van Dokkum and the 3D-HST team. 

What Did Galaxies Look Like at Cosmic High Noon?

The rate of star formation was highest about 10 billion years ago, a period that CANDELS astronomers call “Cosmic High Noon.” The redshift then was about 2, which means that the universe has expanded by a factor of three since then in each of the three spatial dimensions, so it was 3x3x3 = 27 times denser back then. The universe was also much brighter, with so many galaxies so much closer together forming lots of short-lived massive stars, which shine much more brightly than lower-mass long-lived stars like our sun.

What did those early galaxies look like, and how did they evolve into the galaxies we see around us today? Answering that question is one of the most important goals of the CANDELS survey. The infrared capability of the Wide Field Camera 3 (WFC3), installed in the last astronaut visit to Hubble Space Telescope in 2009, gives us the ability to see galaxies at redshift 2 in the wavelengths of visible light. Visible light, with wavelengths ranging from blue at 0.4 to red at 0.7 microns (a micron is a millionth of a meter), gives us crucial information about the long-lived stars in galaxies. The wavelengths of light emitted at redshift 2 expand by a factor of 3, just as space does, so visible wavelengths expand to 1.2 to 2.1 microns. WFC3 allows us to make images at wavelengths as long as 1.7 microns, while WFC3 and other HST cameras make images at shorter wavelengths that allow us to trace recent star formation because such ultraviolet light is emitted by short-lived massive stars.

Simulated galaxy at redshift 2.1 from a high-resolution cosmological simulation.  Top: rest-frame optical
image from the Sunrise computer code, taking in account stellar evolution and the scattering and absorption
of light by dust and subsequent dust re-radiation.  Bottom: The same simulated galaxy, as seen by Hubble
Space Telescope in V (visual light) and H (1.5-1.7 micron infrared wavelengths) bands.  Because of the
redshift of the radiation from this galaxy, what HST sees as V-band light was emitted as ulraviolet in the
galaxy rest frame, which mainly traces new star formation, while what HST sees as H-band light was emitted
as red light, which traces the older stellar population in the high-redshift galaxy.  Note that the V-band image
is clumpy, which is also often the case for real galaxies at these redshifts. Image Credit: Joel Primack

One of the things that we have found is that star-forming galaxies at redshift 2 were often rather clumpy, unlike the rather smooth Milky Way and other nearby galaxies. My colleagues and I have been simulating the formation and evolution of galaxies, and our simulations often also look rather clumpy, with giant star-forming regions in their disks. The clumps occur partly because the galaxies have so much gas in their disks that the disks become gravitationally unstable and break up into clumps of gas that rapidly form stars. We have been comparing the observed and simulated galaxies systematically, and we have been gratified to find that they appear fairly similar in their sizes and shapes, as well as their clumpiness.

Big galaxies today are a combination of stellar disks and spheroids. The Milky Way is a disk galaxy, with a relatively small spheroidal bulge. The most massive nearby galaxies are giant ellipticals, essentially all spheroidal. Most stars appear to form in galactic disks, but today most stars are in galactic spheroids. How did that transformation occur? The standard answer is that when comparable-size disk galaxies merge, their beautiful disks are turned into spheroids as the disk stars go every which way.

In addition to simulating galaxies, my colleagues and I have also run the Bolshoi simulation, the highest resolution large cosmological simulation yet. Using the Bolshoi simulation, we have found that there are not nearly enough galaxy mergers to account for the large number of galactic spheroids. But we have also found that the clumps can rapidly merge onto the galactic centers, which may well be the most important mechanism for forming galactic spheroids. In order to see if this true, and to discover other secrets of galaxy formation, we are running many more galaxy simulations and comparing them ever more systematically with observations. We have also just finished running a new version of the Bolshoi simulation based on the precise new cosmological parameters released by the Planck cosmic microwave background satellite team on March 21, 2013.

Key collaborators on this work: Most of the galaxy simulations were run by Daniel Ceverino, now a postdoc in Madrid. At UCSC my grad student Chris Moody converted them to realistic images taking into account stellar evolution and dust, using our Sunrise computer code; Priya Kollipara measured the sizes and shapes of these images; and Mark Mozena compared them systematically with CANDELS observations under the direction of David Koo and CANDELS Co-PI Sandra Faber.  Avishai Dekel -- with his postdocs Adi Zolotov and Dylan Tweed, his student Nir Mandelker, and others -- has analyzed these simulations and clarified the nature of the disk instabilities that lead to clumps merging to form spheroids. Anatoly Klypin ran the Bolshoi simulation; Peter Behroozi, Sebastian Trujillo-Gomez, and I helped analyze it; and Lauren Porter and Rachel Somerville worked with me on using the Bolshoi simulation to make galaxies semi-analytically.

Reaching out for CANDELS outreach

On May 28th 2013, our blog turned 1! So Jeyhan and I decided, it's time to share what we have done outreach-wise with other people outside the CANDELS team that are interested in Education and Public Outreach (E/PO). At the same time we wanted to see what other people are doing in terms of outreach. And what better opportunity than the annual meeting of the Astronomical Society of the Pacific (ASP). Off we went with our poster under our arms to San Jose, where this year's meeting took place from July 20th to July 24th.

The annual meeting of the ASP is structured very similar to the annual meetings of the American Astronomical Society (AAS, we reported on those here and here). There are plenary sessions which are held in bigger auditoriums, so everyone at the meeting can attend, smaller concurrent sessions that anyone attending chooses according to their own interests and poster sessions during which everyone can come and read your poster and chat with you about it. This year's ASP meeting was special in that it combined two very important topics in one meeting. One half of the conference was called "Cosmos in the Classroom" and all sessions belonging to this category focused more on how to best teach Astronomy in school and college classrooms. The other half was called "Ensuring STEM (Science Technology Engineering Math) Literacy" which was more focused towards general outreach activities, such as our blog. Naturally, the background of the meeting attendants was quite widely spread, there were teachers for every grade, scientists like us that do outreach in their spare time and those that are hired to do outreach professionally. 

Jeyhan in front of our poster. Image credit: J. Pforr

However, the ASP meeting is much smaller in numbers compared to the AAS meetings. Fortunately, that meant that our poster was up all three meeting days and we had ample opportunity to talk and connect to other like-minded people, gather feedback and collect new ideas. 

On our poster we shared what CANDELS is and what our blog is about, what different types of posts we have, etc. We also gave an overview of statistics on the blog, how many people stop by the blog on a daily basis (on average of course), how many people have viewed it since we started and which parts of the world we have reached so far.

"Chat with an Astronomer" Poster at the ASP meeting. You can
see the little iPad next to the poster which connected to the
astronomer on the other side and provided an opportunity to
try it all out. Image credit: J. Pforr

We heard a lot about the outreach other people are doing and stumbled across fun things. One of them was the WorldWide Telescope. Interested parties could put on one of those virtual goggles, were given a game controller, and could fly through the Universe in proper SciFi fashion. 

Another cool thing was the "chat with an astronomer" poster by Genevieve de Messieres from the Smithsonian Institution and her colleagues. They explained how they are using their system at the Public Observatory at the Smithsonian National Air and Space Museum in Washington, DC.  During some of the poster sessions, there was an iPad and a microphone attached to the poster board next to the poster where you could actually talk to and see an astronomer on the other side of the country. I tried it, it worked really well!

The poster right next to us presented a new version of the game MyStar in which you build your own solar systems in our galaxy and can learn a lot about planet formation and extrasolar planetary systems. If you haven't tried it, I suggest you give it a go!

In another corner of the poster exhibition hall, there was a huge inflatable planetarium waiting to be tried out. You already heard more about a similar one in this blog post.

Right next to it, there was a huge blue screen. This was our chance to get recorded while "being in space". So if you stood in front of it, you were interviewed very briefly and filmed. The blue screen was then digitally replaced by an extragalactic space background so it would seem like you're actually in space. If I ever get sent the video of this, I will add it here.

Camilla Corona SDO visiting our poster! Image credit: J. Pforr

But besides all the fun and gadgety stuff to try out we also learned what challenges teachers and educators face when teaching astronomy and sharing their science with the world. We learned how to best put an Astro 101 course together and how to evaluate the success of an outreach project or college course. In interactive group work sessions we shared and found other creative ways to reach more astronomy interested people and how to improve communication.

All in all it was quite an information-packed meeting with lots of interaction. On the last day, we even had a special guest visiting our poster. It was Camilla Corona SDO! For those of you who have not heard about Camilla, have a look here, she's the former mascot of the Solar Dynamics Observatory now turned STEM ambassador, and she was very interested in our poster.  

The Inflativerse - Bringing the Stars to ... Wherever We Want

Today's blog post is somewhat different to what you normally read on this blog. Although this project is not what we (as CANDELS astronomers) technically do for a living, projects like this are an increasingly important part of our job description: Outreach. It's not 'science' as such, but it is an important part of science communication and scientific education. And just as importantly: It is FUN and we hope to encourage people to start a scientific career. Today, I want to introduce to you 'The Inflativerse', a mobile planetarium project that I started at The University of Nottingham while I was still there and which is now being run by a team of astronomy PhD students and undergrad volunteers. But let me start from the beginning.

In spring 2011, we, the Astronomy Group at The University of Nottingham, UK, were asked to participate in a 'Big Bang Science Fair' in Nottingham. This was part of a bigger series of events all through the country. The main part of these fairs is formed by school pupils who present scientific projects. At the same time, the organizers invited scientific departments and organizations to present themselves. 

Astronomy is an area of science where this is usually very easy to do. All we usually need to do is show pretty pictures and give public talks which all of us have up their sleeves and prepared. However, at this particular event, we were explicitly told to NOT present talks, but to present something else. This immediately becomes difficult (Think of it, what would YOU do? If you didn't have any money to do it?). In the end we managed to come up with some nice ideas, offered an 'ask the astronomer' booth (something that I guess every astronomy department has offered many times) and brought different light bulbs and spectrometers for people to look at them. The different light bulbs use different molecules/atoms as lighting material, so their spectra look very different. We were then able to explain how astronomers can use information like this to find out physical properties of astronomical objects. This, however, is a different topic and has been discussed in this blog in a previous post.

More importantly for this blog post, Nina Hatch and myself had this 'crazy idea' over tea when trying to figure out what we would bring to the Big Bang Science Fair: "Wouldn't it be great if we had a small planetarium that we could take to events like this?" We knew some universities had these and they formed the backbone of their respective outreach programs. In fact, Nina had already worked with one of them when she was a student at Edinburgh. What we did not know was where to get one, what they cost, what different versions there are. So, we went home, had a rather extensive search online and found out that not only are there several commercial suppliers of these planetaria, but there was actually quite a variety of different types. There are digital and non-digital, different sizes from 3 meters to about 10 meters across, different domes (some where you have to crawl in, some with a zip as an entrance, some self-standing, some only inflated by themselves -- e.g. deflating when the door is open -- and some that looked like bouncy castles.

For money reasons, we decided to go for a non-digital one. They are usually simply a small light source (in our case a LED) over which you put a filter (basically a big black box with holes, although the brighter stars might have lenses, too). They are about half the price as digital ones, but obviously have the disadvantage that one has to buy particular filters to project particular things, so we couldn't just plug in a laptop and show whatever we wanted. On the other hand, it meant that our 'projection' was not pixelated. I have seen digital planetaria now that use 'old-ish & cheap' projectors and they look terrible, a 'pixel' on the dome is up to 1cm across, hardly what we call 'good resolution'. Today, I am quite happy with our decision. Only recently do projectors have high enough resolution that one could have another go. Only these days have projectors got good enough resolution that one could have another go. More about that at the end of this post.

A Typical Starlab Planetarium.
Image Credit: The Inflativerse Team

We decided to buy a 'starlab.com' planetarium with 10 filters, which came to ~£17000, including some additional equipment like boxes for transport, a small netbook for additional activities, etc.. Plus running costs.

As you can tell, this is rather expensive for the odd event/fair to visit, but at this point we had gotten so excited about the project that we wanted to take it much further than initially thought of. From our web search we knew that several semi-commmercial suppliers in the East Midlands offered planetaria experiences to schools (find out about planetaria in your UK region here), but they all charged the schools £400-£500 for a day, which many schools can't or don't want to spend because they need it for (admittedly) more important issues. We decided to take the planetarium to schools for free in order to offer this experience to many school-kids, tying in with the school curriculum. Specifically, we wanted to target 'Widening Participation' Schools. 'Widening Participation' schemes in the UK are trying to get people from under-privileged areas/schools into university. Most universities have WP programs and contacts at schools, so we would not even have to start from scratch, the contacts were already in place.

So our next task was to find the money. We asked Michael Merrifield, the head of our department, for advice and he suggested a few people to talk to  We contacted two or three people and got a reply from all of them pretty much immediately, some even pointing us onward to the same persons. It turns out (and here's a god tip for departments) that it was (by then) the end of June and the end of the financial year in the UK (or at least Nottingham) is July 31st. That means that some budgets throughout the university had some money left that 'needed' spending and were happy to spend it on projects like this. 'All we needed to do' was write proper proposals for them, which we did straight away, including a pre-invoice and official cost estimate. We managed all this in time and in the end the Nottingham part of HEIF (Higher Education and Innovation Fund) agreed to cover £15000 of the equipment and the School of Physics agreed to cover the rest of the equipment as well as the running costs of the project (e.g. car hires for transport). The only requirement: The equipment had to be delivered (not ordered) by the end of the financial year, which was only about two weeks away at that moment. With lots of help from the UK contact of 'starlab', our finance department, which managed to pay everything as fast as they could, and the starlab shipping team, we indeed made this deadline. (As an additional remark: After we had placed the order, a different grant, the 'University Annual Fund' also agreed to fund the entire project. This Fund is run using alumni donations to the university for projects like this. That means that in the end we would have had enough money to buy a digital planetarium. Now, however, the Annual Fund only had to cover the rest of the equipment, which is why it should be mentioned here, too. And as I said, we are not unhappy with our decision at the time to order a non-digital planetarium.)

Inflating the planetarium for the first time.
Image Credit: The Inflativerse Team

So, by the 1st of August, we had a planetarium at the University, put it up in one of our teaching rooms and simply had a go at it. We were a group of about 8 people, playing with it, trying all the different filters and, admittedly, lying in the dome, gazing at the night sky. I remember I was amazed by the quality of the projection and I think for most of us it was hard to force ourselves to pack it up and go back to work after about 4 hours.

The first two things we needed was another person to help out with organizing the project and a name for the project. Nina was about to start maternity leave and I didn't want to handle it all by myself, firstly because we thought that it was going to be a lot of work and secondly because I was only on a 3 year contract and we wanted some 'consistency' in the project which is easier to achieve with more people where not everyone leaves at the same time. Lucky for us one of our students, Evelyn Johnston, seemed very eager on our test run and after what we thought would require some convincing (but turned out to be simply asking) she agreed to help. We also got Meghan Gray involved as a staff contact to oversee the project. Throughout the 2 years this has been running now, she has given use very good advice at times and in case she reads this, a 'Thank You' is in order. 

Name-wise, we had several ideas, here's a selection: Nottingham Spaceport, Astronomy road show, Star Dome, Stars on Tour, Nottingham Mobile Planetarium, 2π in the Sky, Universe in a Tent, Universe in a Nottshell. You can tell that astronomers are rather bad at making good names. Many of these names were already taken, some even by companies (e.g. suppliers of inflatable domes), which we wanted to avoid. Jamie Ownsworth, one of our PhD students and also a CANDELS member, at some point threw 'The Inflativerse' into the ring (from 'inflating' and 'universe'). Some people didn't like it in the beginning, but over the next days, this became the clear favourite, so we decided to name it 'The Inflativerse' in the end.

Evelyn giving a show (with some spooky light
for the photo, usually it's dark in the dome).
Image Credit: University of Nottingham

Through contacts at our university (mainly Lisa Owen, 'Thank You' to you, too!), we started to contact schools and immediately found that this project was rather popular. As already planned, we recruited a larger team of volunteers, in this first year from our own department, ending up with about 12 people (including Several CANDELS members, Alice Mortlock, Jamie Ownsworth, Will Hartley, myself) for the 12 school visits that we had proposed for the first year of the project. So over all, pretty small time constraints were needed from each volunteer, about 3 school visits/year. It became clear that we would be rather man- (and woman-) power limited -- we could have visited many more schools even in this first year. Without even pushing. We never really advertised the planetarium anywhere other than through direct contact and word-of-mouth from teacher to teacher. Yet the requests keep coming in and many people find us through our website.

In order to be able to start school visits in September/October, we immediately started to develop some shows that we could present to kids of different ages. We had decided to target years 4 and 9, but soon found out that schools teach astronomy in different years, so I think by now, we have visited kids of all ages, including a nursery. I think our first attempts of shows felt rather clunky, but with experience and confidence they got better and better in the end. On our first school visit to the Nottingham University Samworth Academy -- a school connected to the University of Nottingham and the only non-WP school that we visit -- two film makers made videos about us, one from the school and one sent by Brady Haran (a film maker who runs the youtube channel sixtysymbols). You can find both videos here and here.

[This is the point where I have to put something straight: When the above videos came out, MANY blogs -- just google "Inflativerse" -- posted about us. In a process where people simply copy information from other blogs, most of them stated that we had actually developed the dome and projector. We have NOT. It's a bought system, we only turned it into a cool event for schools, but even there we are by far not the first ones. St. Andrews and Edinburgh had their projects running for years, and I am sure there are even older ones than that. While we are not the oldest, I think we do have the coolest name ;-) ]

This is the Greek mythology filter. Unfortunately it is very
hard to take a picture of the normal sky field, so I can't show
one here. Image Credit: The Inflativerse Team

Over the months, standard visits developed. We would take the younger kids on a trip through the night sky and the Greek myths that are connected to the constellations (a great book to be recommended in this context is 'The Mythology of the Night Sky'), while carefully avoiding the not so child-friendly bits (the stories are over all rather gory and include a lot of stuff not quite suitable for 8 year old kids). For the older kids, we include some of the same stories, but on top of that, we include much more about physical processes. This is a short list of topics we can (and regularly did) cover: The sky at night, Constellations, how to tell a star from a planet, Ancient Greek mythology, Light pollution, Constellations, Navigation by the stars, Phases of the moon, Our Galaxy - the Milky Way, "How do I become a scientist?", Changing seasons, Temperatures of stars, star clusters, nebulae, stellar nurseries and many more. 

Our ocean current filter. Image Credit: The Inflativerse Team

But we have filters for more, e.g. ocean currents and plate tectonics, and can implement many other topics into the shows. One of my personal favourites is 'Harry Potter on the night sky' and 'Tolkiens Sky', featuring many names from Harry Potter books that are taken from constellations and stars (a surprising amount!) or the constellations and stories explained in the Lord of the Rings and other Tolkien stories (Probably something I should pick up again and work out in a bit more detail, given that I moved to Oxford and Tolkiens home-pub is 100-200 meters from my desk).

Throughout the entire process, I personally found it very positive that, while we did write down some of the shows, we never forced people to stick to exact scripts. We wanted every single presenter to be comfortable in his show and make up his own script. While this meant that we had a slightly longer learning process, it made sure that we came across as enthusiastic rather than a robot that just repeats what he's told.

In addition to our planetarium shows, we have developed some other activities that can be run either in a classroom or outside the building. One of our favourites here is a scaled version of the solar system. We use a football (a proper, 'soccer' football) as the sun and then, while talking the kids through each planet from the inside out (we show pictures on an iPad or small laptop), we walk them through the scale model of the solar system. At this scale, the Earth is a bead 2mm across at a distance of 23.5 meters, which gives the kids a rather good impression of how empty space actually is, even in a 'crowded place' like the solar system. We also own a real piece of space junk (a piece of an asteroid found in Argentina and sold on ebay) which we usually pass around in that context.

Last year, we re-organized the team, now recruiting undergrad students as well, and the project has been very successful over all. Over the last 2 years, we have visited 24 schools and several public events, amongst them 'Nottingham Light Night', 'BBC stargazing live' 2012 & 2013, University Mayfest 2012 & 2013,  with a total number of ~4000 visitors into the planetarium. We also had several Brownie groups visit the university for a planetarium visit and the dome was used for the 'brain awareness week' (They called it InflatiBrain) by a different department. They didn't project the stars, they projected the structure of the brain. But our achievements are not only of public type, we (Jamie Ownsworth) have also given a talk at the IAU in Beijing (one of the largest conferences in astronomy), so I hope we are leaving some imprint on professional astronomers, too. Maybe someone will follow our example and build up their own 'Inflativerse'. It has been a lot of fun for all of us (while at times it was rather a lot of work) and I think both the department and the community benefit massively from such a project.

Additionally, I have to mention that we personally all benefited from it, too, and I have to thank all the volunteers in this project for their great efforts and for helping us run the Inflativerse over the last 2 years. All our volunteers have done great work and I am sure their school visits and the experience gained will benefit them in their future and if it's only from being more confident to talk in front of bigger crowds. Evelyn was nominated for the 'IoP Very Early Career Physics Communicator Award' for her work and I myself have managed to secure a 3 months outreach fellowship from the university in the first year in order to start up the project and set it up it as a sustainable outreach program. Recently, all 3 of us were also told that we will receive the Vice-Chancellors Achievement Award from the University of Nottingham for the project, something, I have to say, that I feel rather proud about. Without the help from all our volunteers, I am sure non of this would have happened. More generally, outreach projects like this look very good on a CV and, as they become more and more important in our jobs, are a valuable skill when applying for jobs. So to all the astronomers and all other scientists who read this: you can see, that this kind of outreach work can and will be rewarded on some level or the other. While people always complain that outreach is 'not their job' and 'a waste of (research) time', it seems to help to keep us in a job, so everyone out there, please keep up the good work.

As I mentioned above, I have meanwhile moved away from Nottingham, so 'The Inflativerse' is not in my hands anymore, but I keep strong personal links and sometimes still wear my Inflativerse T-Shirt with pride. Oxford, where I am now, co-owns one of these domes, too, but they do not take it to schools as we did in Nottingham. Occasionally, we get classes visiting here and we use it for open days, but on a much lower level than in Nottingham. However, techniques have progressed and affordable projectors are now good enough to be used in a planetarium context. We took a look into upgrading our starlab system (an older version of the one used by The Inflativerse) to a digital projector and have actually already ordered all the parts. For ~£2000, we bought a HD projector and some optics (including a fish-eye lens) and we will soon build a digital system ourselves instead of buying the $40000 commercial versions. We have to hope a bit that this works in the end, but we are optimistic, given that we have people in the workshops that have built MUCH more complicated optical system than that, e.g. scientific instruments for telescopes. 

The ultimate goal here (besides using the more flexible system in-house) is to pre-record shows and train teachers on using the dome so that they can borrow the planetarium and run school events themselves. We have all the parts here now and will be starting on this pretty soon. When we have a working system, we will also try to distribute the plans and links to the community, maybe someone else (maybe even Nottingham) is willing to spend money on this 'low-budget' digital system and share their pre-recorded shows, hopefully building up a great database for the future. But this is my next project and should be discussed once it's running in a separate blog post.