CANDELS Finds the Most Distant Type Ia Supernova Yet Observed

Image credit: NASA

A couple weeks ago, the supernova science team from CANDELS was pleased to announce the discovery of the most distant Type Ia supernova ever seen at more than 10 billion light years away, a time when the universe was only about 3.5 billion years old. There wasn't ever much doubt that supernovae existed more than 10 billion years ago -- but it's still an exciting moment for us when we're able to photograph one with the Hubble Space Telescope. The image on the right shows the supernova's location in one of the five fields that CANDELS is searching. Almost every single dot in the upper panel is a distant galaxy, filled with billions of stars. Our team searches through these images every couple of months, hoping that one of these stars has exploded.

But ironically, the most exciting thing about this supernova for many of us is that we haven't seen more. In terms of gaining an understanding of how these objects are created, its really the lack of supernovae in the early universe that is the most telling observation. The Hubble has the power to observe one of these objects from more than 11 billion light years away, and we've been staring at the sky in search of them for nearly 3 years. So far, we've found only a single confirmed Type Ia supernova from 10-11 billion years ago -- a billion years of cosmic history.

In astronomy, our uncertainty about the universe is somewhat striking. 70% of the Universe is the mysterious "dark energy", completely unknown until about 15 years ago. Another 25% is dark matter -- also a mystery, since we only observe its gravitational effects. This leaves 5% of the universe that is composed of matter more familiar to us. In the context of this uncertainty, the supernova progenitor mystery might not seem so fundamental. And yet, every second, about 5-10 supernovae are going off somewhere in the observable universe with 10 billion times the brightness of our sun. These supernovae produce about half of the iron in the universe, some of the raw material for creating planets like the Earth. And the ways that these explosions happen -- both the stellar evolutionary steps that lead to the explosion and the physics of the detonation itself -- remain mysterious.

The composition of the universe.  Only 5% of the universe is normal matter, and only .03% of the universe consists of the heavier elements we're most familiar with on Earth.
Image source: http://www.lsst.org/lsst/public/dark_energy

This dearth of supernovae must be telling us something fundamental about the nature of these objects -- so what is it? Finding the earliest supernovae sheds light on this puzzle in a couple of different ways because fundamentally, the early universe was a very different place than the universe we live in today. There were fewer heavy elements, stars were younger, and galaxies were producing stars at a faster rate than they are today. The way in which supernovae form in this environment tells us something about their nature.

First of all, if supernovae are formed from younger stars, do they explode in the same way? Some theorists think that the answer is no -- it's predicted that only more massive stars have time to become supernovae within the first 3-4 billion years of the Universe, and nuclear fusion in more massive stars will result in a different blend of heavy elements in the core.  When the star's remnant (called a white dwarf) gains matter from a binary companion and explodes, its brightness is powered by the radioactive decay of elements fused in the explosion; a different chemical composition results in a different brightness. We're looking for such a change in brightness -- it can tell us a bit more about how supernovae are created.

Secondly, if a burst of star formation occurs in a galaxy, how long will it be before the Type Ia supernovae start exploding? How quickly stars evolve and form supernovae can tell us a lot. If most Type Ia supernovae occur when two white dwarfs form in a binary system and then slowly merge together, the time it takes them to explode will be based on the distribution of initial separations that binary stars are born with. If, on the other hand, they tend to occur when a normal or giant star is slowly pouring mass onto a white dwarf at a given speed, one might expect something closer to a single characteristic time from formation to explosion. By knowing when most of the stars formed in the universe, and observing how quickly supernovae are exploding at different ages of the universe, we can determine which model for supernovae is correct. This knowledge may also make it easier to understand the physics of a white dwarf's detonation.

All of this work can be tied back to the fact that Type Ia supernovae are not just interesting in and of themselves; they are cosmological tools with a characteristic brightness that can be used to set a distance scale for the Universe. Understanding better how supernovae explode can be used to answer questions like: why are supernovae dimmer in smaller galaxies? What process creates unpredictable and unusual supernovae like Type Iax? How can we better calibrate these tools to learn more about dark energy?

These are some of the questions that our team hopes to answer in the coming years. In the meantime, we're searching the night sky for exploding stars -- and each time we find one, it tells us a bit more about the universe we live in.

Teaching Astronomy at a Liberal Arts School

Colby College, Miller Library
Image credit: E. McGrath

Recently, I was lucky enough to land my dream job — professor of physics and astronomy at one of the nation’s top-tier liberal arts schools. I’d be lying, however, if I said there weren’t quite a few adjustments to make in the transition from postdoctoral researcher at the University of California, Santa Cruz to assistant professor at Colby College in Waterville, Maine. This new career is challenging and exciting on several different levels. Many people may not realize that a professor’s life does not just include preparing lectures, holding office hours, and grading papers. There are all sorts of other commitments, including service to the college, guiding undergraduate students through their first research projects, attracting external funding, and carrying out your own robust research program. These are neither optional, nor is it sufficient to be good at any single aspect; in order for the college to succeed as an institution, we hire folks who we think will excel in all of these areas, thereby bringing further prestige and attracting better students to the college.

As a new professor, the biggest challenge so far has proven to be time management — prioritizing and fitting all those various commitments into a manageable schedule. A typical day for me consists of something like the following: four hours of lecture preparation, two hours in class lecturing, two hours of grading or composing exams and homework assignments, two hours meeting with students individually, one hour of committee meetings, and a couple hours devoted to my own research (much of which is done after hours). The astute among you will notice those numbers do not add up to a typical 8-hour workday!

This winter I also sat on a hiring committee for the Mathematics and Statistics Department here at Colby. My job as the “outside” member of the committee was to provide a different perspective on the qualifications of our candidates and decide whether they would be a good “fit” for Colby. Since STEM fields tend to be poorly represented by women and minorities, I was also asked to serve in order to diversify the committee. We reviewed over 250 applications for a single-year sabbatical replacement position. I was amazed at how many outstanding applications we received, and appalled that so many of these highly skilled men and women still did not have permanent positions. It is indeed a tough job market out there!

Other service activities in which faculty are involved include campus-wide committees that address everything from admissions procedures, to curriculum development, to information technology, to promotion and even dismissal hearings. Still other responsibilities include advising students and writing recommendation letters as they apply for jobs and graduate school. As a first-year professor I have been spared many of these tasks while I’m still “learning the ropes,” but I will become more active in these areas over the coming years.

Liberal arts schools like Colby also place a great deal of importance on maintaining an active research program. We are, after all, training the next generation of scientists, which cannot be accomplished in the classroom alone. Maintaining a research program that is not only accessible to students, but also tackles important and exciting questions in your field is imperative. Luckily, it is also one of the most enjoyable aspects of being a scientist, so it is easy to stay motivated.  Since much of the semester is devoted to more traditional teaching and service activities, I take advantage of the breaks to advance my research. This past January, for instance, I traveled to Sesto, Italy to present the results of my research at the Star Formation Over Cosmic Time meeting. And during spring break, I traveled back to UC Santa Cruz to meet with collaborators and discuss science. This summer there are a number of grant proposal deadlines on which I will spend a significant amount of time. Being able to fund your research is another important aspect of life as a professor. You are expected to bring in grant money that will not only pay for things like salary, equipment, travel, and publication costs directly related to your research, but will also support services used by the entire campus community.

NGC 6946, the Fireworks Galaxy.
Image taken by AS 231 students at Colby College.

In the end, what makes it worth all the long hours and hard work is the sheer joy of imparting pieces of knowledge to my many enthusiastic students, and seeing them get excited about science, sometimes for the first time. In my Astrophysics class last fall, for example, I held a number of labs at Colby’s small observatory, where students learned how to collect their own data, process, and analyze it using the tools of professional astronomers. The image of NGC 6946, pictured to the left, is one of the results of these labs. The skills we teach these young students, including critical thinking, experimental design, computational analysis, and technical writing will serve them well no matter where their lives take them after Colby. It is my hope that they will also have some fun along the way.

Astronomer of the Month: Romeel Davé

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 Romeel Davé.

Tell us a little about yourself!

Hi, I'm Romeel Davé, and I am currently the South African National Research Chair in Cosmology with Multi-Wavelength Surveys. I just moved to this mouthful of a new position in January from the University of Arizona in Tucson, where I was a professor.  Though it is a bit scientifically isolated as I am striving to build up a group here in Cape Town, I nonetheless feel lucky to live in one of the most beautiful cities in the world with a great quality of life, doing what I love. Before becoming a professor, I held postdoctoral fellowships at Arizona (Hubble fellow) and Princeton (Spitzer fellow). I got my Ph.D. in Astronomy from U.C. Santa Cruz, M.S. Physics from Caltech, and A.B. Physics from Berkeley (Go Bears!). I also attended the University of Texas, San Jose State University, and Foothill Junior College in my rather circuitous academic journey. My father is from India (Gujarat), my mother is from America (Nebraska), and I grew up everywhere from California to Massachussets to Texas to India. I enjoy basketball, whitewater and other water sports, the outdoors, and good beer and wine. In my misspent college days I did a lot of theater, acting, directing, and being in an improv comedy troupe that did gigs around town. I enjoy traveling, and have taken trips to Eastern Europe (right after the Wall fell), Indonesia, West Africa, and other amazing locales. I am married and have two young daughters, so I have less time for my hobbies now, but I tell myself that parenting is my most rewarding hobby yet. Occasionally, I even believe it.

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

I am a computational galaxy formation theorist. I use large supercomputers to try to model the universe from the Big Bang until today. I am particularly interested in how galaxies form and evolve, because galaxies are the way in which we observe and mark out the distant Universe with surveys like CANDELS. My current work pushes the idea that galaxies are born, grow, and die within a cosmic ecosystem of surrounding gas, with which they continually exchange mass and energy in a way that regulates their growth and establishes
their observable properties. This "baryon cycle" approach to understanding galaxy evolution has been a key new development in recent years, and I'd like to think I'm on the leading edge of this. My role in CANDELS is to provide numerical simulations of galaxy formation to be compared with CANDELS data. This allows us to both test and constrain the baryon cycle view of galaxy evolution, and provide insights into the physics that sets the observable properties of galaxies across cosmic time as seen by CANDELS.

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

As a kid growing up in light-polluted suburbia, I was never particularly interested in the night sky. Starting in high school, I wanted to be a string theorist, because it seemed like a fundamentally new way to understand the universe at the deepest level. But once I got to graduate school at Caltech, I became disenchanted by the vast disconnect between string theory and experimental particle physics. It didn't seem like string theory was directly testable in any sense, which was a bit unsettling for a purported theory of science.  Meanwhile, on a lark I stumbled into a course on Cosmology, and realized that this field had a remarkably active and close connection between observers and theorists. Also, it seemed that computers, which were another hobby of mine, could play a key role in understanding the evolution of our universe. So I joined Tony Readhead's group working to measure the Cosmic Microwave Background using radio telescopes at Owens Valley. This convinced me that a) astronomy was pretty cool and interesting, and b) I am not cut out to be an observer because I hate reducing data! So eventually I transferred to Santa Cruz to become a theorist, specifically using computer simulations to constrain cosmological parameters. By the end of grad school, thanks to the COBE and WMAP satellites, cosmology started becoming more of a "precision" science, i.e., we know what we need to measure, we just need to measure it ever more precisely. I found this sort of "cosmic bean counting" work rather dull so I moved on, although I am glad there are people who like it because I'd really like to know the answer! In the meantime, galaxy formation caught my eye as a much more complex and wide-open area, so after my Ph.D. I started working on that, and it has held my attention ever since. I am lucky to have landed in a field that allows me to use my talents and interests while providing the intellectual challenge of working on some of the greatest mysteries in the Universe.

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

Honestly, I've been pretty fortunate in my career, I can't think of any big obstacles. I've always been confident in my intellectual ability, so it's mostly been a question of deciding what I wanted to do. I've had some helpful teachers and mentors, and though I've also had my share of poor and negative ones, who I basically just tried to ignore. I had two supportive parents even though they divorced when I was very young, and a reasonably comfortable upbringing even though I never attended the same school two consecutive years until 9th and 10th grade. I had a bit of a life crisis after I quit Caltech with my consolation Master's, because the experience was so negative both personally and professionally that I started to question whether I wanted to be an academic at all. Eventually, I found that astronomers were a bit more friendly and cool than physicists (yes, I know that's a low bar), and after taking a year off, I dove back into graduate school in astronomy at Santa Cruz with renewed energy. But the year away taught me that in order to be successful in my career, I also had to live a full and enjoyable life. Achieving that life-work balance has been crucial for me ever since, and I think it's worked out fairly well so far.

Who has been your biggest scientific role model and why? 

Probably my most significant role model was my Ph.D. advisor, Lars Hernquist (now at Harvard). Watching him, I learned the "game" of astronomy, that is, what one needs to do in order to succeed besides just doing good work. I learned to focus on being careful and correct rather than being loud or first. I learned that it's crucial to pick the right problem to work on, something where you can make meaningful contributions but also that others will find interesting and useful. My stock advice to budding theorists is that there is nothing more useless than a dull theorist -- not all of your ideas have to be right, but they should all be interesting and provocative. So don't be afraid to think outside the box, and to trust your intuition over the accepted dogma. However, there is a fine line between being provocative and being a blowhard. It's therefore important to have a deep understanding of both the current literature and the fundamental physics, to never stop expanding your knowledge base, and to always try to be your own harshest critic. Many of these things I learned by watching Lars, but I've also seen them reflected in many senior colleagues that I respect the most, including CANDELS PI Sandy Faber.

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

Definitely my favorite aspect is the time-flexible, travel-oriented lifestyle. Face it, as astronomers we're overworked and underpaid, and until tenure it can be an uncertain and itinerant lifestyle that is not conducive to settling down with a family. So why do it? Why not make double or triple being a hedge fund manager or software guru, working fixed hours with weekends free? Many of my friends have chosen that path, but for most of them, it's been bittersweet. The best part about being an astronomer, or really an academic researcher in general, is that you get to work on your own schedule, and you are only judged by your long-term body of work. This means that you can take time off for a sick kid, or take extra time to see sights when you travel to a new place. That's not to say there aren't deadlines and goals, but the day-to-day time pressure is less than in the "real world". Also, the freedom of intellectual exploration, to be able to decide for yourself what to work on, is something that I very much cherish. I generally find the people to be great too. Of course there are the occasional jerks that you find in all walks of life, but I've made a lot of good friends that I enjoy hanging out with socially. I look forward to CANDELS team meetings and other conferences not only for the intellectual stimulation, but also for catching up with old acquaintances as well as making new ones.

What motivates you in your research? 

Basically, I love to think about things, and I love an intellectual challenge. It's hard for me to imagine a bigger one than figuring out how the whole Universe works. My brain loves to think about stuff in the background; many times I've woken up in the middle of the night and gone "hey, I just realized how to solve that problem!" And certainly, there is a (friendly) competitive aspect to it, especially as a theorist whose ideas are constantly being tested against others' by ever-improving observations. It's fun to be right on occasion, although it's dangerous to get too cocky since the next new data set could always rule out the model I'm currently pimping!

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

Probably the original Lick Observatory 36" refractor. I worked as a tour guide there during the year off I took from grad school between Caltech and Santa Cruz. The old telescope is truly a work of art with its elevating wood floor, not to mention the odd creepiness of James Lick being buried underneath it.  Also, my girlfriend (now wife) observed there for her thesis work, so I have fond memories of nights by ourselves at the telescope. Diligently working to solve the mysteries of the cosmos, of course.

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

As a SARChI chair in Cape Town, I basically have to build a galaxy formation group from scratch, in a country (actually, a continent) that has an enthusiastic commitment to astronomy but still relatively meager resources. My goal is to make Cape Town a hub for galaxy formation theory as much as Arizona or its equivalent. I don't expect it to happen overnight, but with lots of groundwork and a little bit of luck, I hope to make substantial progress in the time I'm here. A critical challenge in South Africa is human capital development; unlike in the USA and Europe, there is not a large population of highly trained young scientists who are eager to do astronomy, as it is still regarded (like most pure science research) as a somewhat esoteric and frivolous field, and the best young students are typically directed into more "practical" professions. Hence in a broader context it is important for Africa to have a forefront presence in international astronomy, in part because the next great radio astronomical facility being planned, the Square Kilometer Array, will be primarily hosted in South Africa, but also because it is sociopolitically important to raise the educational and research infrastructure in South Africa (and Africa in general) to be internationally competitive in order to help transition from a third-world "resource based" economy to a first-world "product based" economy. That I might play a small role in this was one of the reasons I was attracted to this position.
 

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

That the diversity of people who do astronomy would reflect the diversity of the overall population in terms of race, color, and gender. This is critical not only to ensure the widest talent pool, but also to make the field more interesting and enjoyable by having a wide range of backgrounds and working styles represented.

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

That the laws of physics as we know them allows us to trace the evolution of the Universe back to a mere 10^-43 seconds after the Big Bang. To me, that is just a stunning triumph of modern physics. But it also begets perhaps the greatest question of all: What came before the Big Bang?

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

In my copious spare time I help produce documentaries focused on the lives and science of minority astrophysicists. Our latest movie is Black Sun, which follows two African-American solar physicists to Tokyo and Cairns as they do solar physics experiments during the 2012 solar eclipses.  You can find out more about this exciting film (and follow us on Facebook and Twitter) at http://www.BlackSunMovie.com.

On Mountain Tops and Lasers

The Subaru Telescope (left) next to the two Keck Telescopes on Mauna Kea.
Image Credit: J. Pennington

Tonight I am sitting on top of a 14,000 foot mountain observing distant galaxies. This is the second of a three night run at the Subaru Telescope on Mauna Kea on the Big Island of Hawaii. In a previous post I talked about a run to obtain spectroscopy on one of the Keck Telescopes and some of the excitement, including ups and downs, that are part and parcel of an observing run. This run is no exception!

Initially, my collaborators from the University of Hawaii and I proposed to obtain near-infrared spectroscopy of distant luminous and ultraluminous infrared galaxies using an instrument called FMOS. Due to a problem with the telescope, that instrument turned out to be unavailable during this run so we had to scramble to change our science program to use a completely different instrument. I'm sure I'll talk more about FMOS in the future, but for now I'll focus on what we're doing this week!

The instrument we are using is called IRCS - the Infrared Camera and Spectrograph. We are only using the imaging mode of this camera. The exciting thing about this run is that we are also using the Laser guide star adaptive optics system on Subaru. Briefly, adaptive optics is a technique used by astronomers to obtain images at a higher resolution (and therefore allows us to study features at greater detail) than we normally can from the ground. Since we have to observe through the Earth's atmosphere, our images are blurrier than they would be from space. The reason for this is that the turbulence of the atmosphere causes the light from distant objects to shift in position on a very short timescale (this is why stars twinkle!). As you take an image with a camera on a telescope, this shifting adds up, causing the resulting image to be blurry. Ever notice how a picture on your digital camera is blurry if your subject moves while you are taking it?

Image of the nuclear region of a nearby galaxy (NGC 7469) taken with
and without adaptive optics at CFHT.
Image credit: Center for Adaptive Optics

We can counteract some of this by placing our telescopes on top of tall mountains (such as Mauna Kea) and therefore above some of the atmosphere. We can improve on this even more by using adaptive optics. Adaptive optics uses a bright star to correct for the effects of the atmosphere. Since we know what a star is supposed to look like (it should be point-like in images), the distortions introduced by the atmosphere can be calculated and a deformable mirror is re-shaped so that the light goes where it's supposed to. These corrections can result in images almost or just as sharp as those taken from space (check out the example to the left)! However, since the turbulence of the atmosphere is different at every point on the sky, in order to make these corrections you need to have a bright star that is very close to the object you are trying to observe. This isn't always possible and can be very difficult in our deep fields. This is where Laser Guide Star Adaptive Optics comes in!

Laser from the Subaru Telescope
Image credit: D. Birchall

Laser Guide Star Adaptive Optics is used to create an artificial star close to the object you are observing anywhere in the sky. A bright star is still needed, but it can be a little fainter and a little farther away. This technology has opened up a much larger area of the sky for this kind of imaging! As I am typing this, there is a laser from Subaru aimed at the target I am observing. Keck is also using their laser tonight. You can often see these lasers in images of the telescopes (such as the ones to the right and below).

Tonight we are targeting galaxies within COSMOS and EGS that fall outside of the CANDELS WFC3 HST coverage. In this way, we can obtain high resolution near-infrared images of select interesting targets in order to study their morphology in detail. These galaxies are all sources with extreme infrared luminosities and with this data we will be able to search for signatures of galaxy mergers and study the properties of any star-forming clumps we detect. Our first night was lost due to some problems with the dome shutter but those problems have been fixed and tonight we making our way through our list of targets! 

Using the laser always makes for a particularly busy night of observing because there are many things to consider when shining a bright laser into the sky. First of all, all of our targets must be submitted to Space Command for approval ahead of time to insure that the laser does not interfere with any passing satellites. Because of this, there are certain times of the nights where we must pause our observations or switch targets. We also have to be careful about any planes that might be passing overhead. While the laser is shining, there are always a couple of people standing outside watching, ready to turn off the laser just in case. So far, tonight is going pretty well and the forecast looks great for tomorrow as well!

Panoramic image showing lasers from Subaru and both Keck Telescopes. Image Credit: D. Birchall