Friday, April 4, 2014
Center for Student Services 360 (Workshop Space) – Center for Student Services

Spring TA Training

Tuesday, April 1, 2014
Center for Student Services 360 (Workshop Space) – Center for Student Services

Spring Head TA Lunch

Galaxies on FIRE: Star Feedback Results in Less Massive Galaxies

For decades, astrophysicists have encountered a puzzling contradiction: although many galactic-wind models—simulations of how matter is distributed in our universe—predict that the majority of the "normal" matter exists in stars at the center of galaxies, in actuality these stars account for less than 10 percent of the matter in the universe. A new set of simulations offer insight into this mismatch between the models and reality: the energy released by individual stars within galaxies can have a substantial effect on where matter is located in the universe.

The Feedback in Realistic Environments, or FIRE, project is the culmination of a multiyear, multiuniversity effort that—for the first time—simulates the evolution of galaxies from shortly after the Big Bang through today. The first simulation to factor in the realistic effects of stars on their galaxies, FIRE results suggest that the radiation from stars is powerful enough to push matter out of galaxies. And this push is enough to account for the "missing" galactic mass in previous calculations, says Philip Hopkins, assistant professor of theoretical astrophysics at the California Institute of Technology (Caltech) and lead author of a paper resulting from the project.

"People have guessed for a long time that the 'missing physics' in these models was what we call feedback from stars," Hopkins says. "When stars form, they should have a dramatic impact on the galaxies in which they arise, through the radiation they emit, the winds they blow off of their surfaces, and their explosions as supernovae. Previously, it has not been possible to directly follow any of these processes within a galaxy, so the earlier models simply estimated—indirectly—the impact of these effects."

By incorporating the data of individual stars into whole-galaxy models, Hopkins and his colleagues can look at the actual effects of star feedback—how radiation from stars "pushes" on galactic matter—in each of the galaxies they study. With new and improved computer codes, Hopkins and his colleagues can now focus their model on specific galaxies, using what are called zoom-in simulations. "Zoom-in simulations allow you to 'cut out' and study just the region of the universe—a few million light-years across, for example—around what's going to become the galaxy you care about," he says. "It would be crazy expensive to run simulations of the entire universe—about 50 billion light-years across—all at once, so you just pick one galaxy at a time, and you concentrate all of your resolution there."

A zoomed-in view of evolving stars within galaxies allows the researchers to see the radiation from stars and supernovae explosions blowing large amounts of material out of those galaxies. When they calculate the amount of matter lost from the galaxies during these events, that feedback from stars in the simulation accurately accounts for the low masses that have been actually observed in real galaxies. "The big thing that we are able to explain is that real galaxies are much less massive than they would be if these feedback processes weren't operating," he says. "So if you care about the structure of a galaxy, you really need to care about star formation and supernovae—and the effect of their feedback on the galaxy."

But once stars push this matter out of the galaxy, where does it go?

That's a good question, Hopkins says—and one that the researchers hope to answer by combining their simulations with new observations in the coming months.

"Stars and supernovae seem to produce these galactic superwinds that blow material out into what we call the circum- and intergalactic medium—the space around and between galaxies. It's really timely for us because there are a lot of new observations of the gas in this intergalactic medium right now, many of them coming from Caltech," Hopkins says. "For example, people have recently found that there are more heavy elements floating around a couple hundred thousand light-years away from a galaxy than are actually inside the galaxy itself. You can track the lost matter by finding these heavy elements; we know they are only made in the fusion in stars, so they had to be inside a galaxy at some point. This fits in with our picture and we can now actually start to map out where this stuff is going."

Although the FIRE simulations can accurately account for the low mass of small- to average-size galaxies, the physics included, as in previous models, can't explain all of the missing mass in very large galaxies—like those larger than our Milky Way. Hopkins and his colleagues have hypothesized that black holes at the centers of these large galaxies might release enough energy to push out the rest of the matter not blown out by stars. "The next step for the simulations is accounting for the energy from black holes that we've mostly ignored for now," he says.

The information provided by the FIRE simulations shows that feedback from stars can alter the growth and history of galaxies in a much more dramatic way than anyone had previously anticipated, Hopkins says. "We've just begun to explore these new surprises, but we hope that these new tools will enable us to study a whole host of open questions in the field."

These results were submitted to the Monthly Notices of the Royal Astronomical Society on November 8, 2013 in a paper titled "Galaxies on FIRE (Feedback In Realistic Environments): Stellar Feedback Explains Cosmologically Inefficient Star Formation." In addition to Hopkins, other authors on the paper include Duìan Kereì, UC San Diego; José Oñorbe and James S. Bullock, UC Irvine; Claude-André Faucher-Giguère, Northwestern University; Eliot Quataert, UC Berkeley; and Norman Murray, the Canadian Institute for Theoretical Astrophysics. Hopkins's work was funded by the National Science Foundation and a NASA Einstein Postdoctoral Fellowship, as well as the Gordon and Betty Moore Foundation.

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Friday, January 24, 2014
Beckman Institute Auditorium – Beckman Institute

2014 Frontiers in Nano Science and Technology

John H. Schwarz Wins the Fundamental Physics Prize

John H. Schwarz, the Harold Brown Professor of Theoretical Physics at Caltech, and Michael B. Green of the University of Cambridge have been awarded the 2014 Fundamental Physics Prize in recognition of the new perspectives they have brought to quantum gravity and the unification of the fundamental physical forces of the universe. The prize comes with a $3 million award.

The prize was announced at an award ceremony at NASA's Ames Research Center in Silicon Valley on December 12. Alexander Varshavsky, Caltech's Howard and Gwen Laurie Smits Professor of Cell Biology received the 2014 Breakthrough Prize in Life Sciences at the same ceremony. Schwarz and Green were awarded the Physics Frontiers Prize earlier this year, which admitted them to candidacy for the Fundamental Physics Prize. The 2014 Physics Frontiers Prize was also awarded to Joseph Polchinski of the University of California, Santa Barbara, a Caltech alumnus (BS, 1975).

The Fundamental Physics Prize is awarded by the Fundamental Physics Prize Foundation, which was established in July 2012 by Russian physicist and Internet entrepreneur Yuri Milner to recognize groundbreaking work in the field. Previous winners include Caltech's Alexei Kitaev, the Ronald and Maxine Linde Professor of Theoretical Physics and Mathematics. He and the other recipients of the award—including theoretical physicist Stephen Hawking—served on the selection committee for this year's prize.

Schwarz and Green were honored for developing superstring theory during their collaboration between 1979 and 1986. Its predecessor, string theory, originated in the late 1960s in response to the discovery of many new particles via accelerator experiments. Theoretical physicists, says Schwarz, tried "to make order out of all this chaos" by postulating that the fundamental object of the universe is the string and that the various particles in the universe could be adequately described as different oscillation modes of the string. It was thought for a time that string theory would yield an explanation of the strong nuclear force that binds protons and neutrons together in an atom's nucleus (or even more fundamentally, the quarks and gluons that make up protons and neutrons). But then in the mid-1970s, quantum chromodynamics provided an excellent account of the strong nuclear force, and string theory fell out of favor among most theoretical physicists.

In 1974, Schwarz and his then collaborator, Joel Scherk, suggested a different possible use of string theory: a quantum theory of gravity and the unification of all the forces in nature. To follow up on this suggestion, Schwarz began his collaboration with Green in 1979, and together they created superstring theory, a version of string theory that relies on the property of supersymmetry to relate the two fundamental types of particles in quantum theory—bosons and fermions—to one another.

According to Schwarz, this is "a very ambitious project, and not something that's going to be completed in my lifetime." But, he says, "people are making lots and lots of progress. We keep discovering new things about superstring theory, which give us the sense that we're closing in on something really important." Indeed, experimental physicists working on CERN's Large Hadron Collider may soon be able to prove the existence of supersymmetry, which, says Schwarz, "wouldn't prove that superstring theory is right, but would be extremely encouraging."

This optimism regarding the ultimate success of superstring theory has not always been shared throughout the scientific community. When Schwarz and Green began their work together in 1979, it was, says Schwarz, "not particularly fashionable or popular." But in 1984, the pair's discovery of the so-called Green-Schwarz anomaly cancellation mechanism brought new excitement to superstring theory. "It has remained popular ever since—30 years later," Schwarz remarks.

Schwarz notes that he is especially honored to receive the Fundamental Physics Prize because "the people who were making the selection were other theoretical physicists who've already won the prize, and they are people that I respect and admire. Being chosen by them is particularly meaningful." Schwarz and Green are now eligible to serve on the selection committee for future Fundamental Physics Prizes.

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Cynthia Eller
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Massive Galaxy Cluster Verifies Predictions of Cosmological Theory

First Detection of the Kinetic SZ Effect in an Individual Galaxy Cluster

By observing a high-speed component of a massive galaxy cluster, Caltech/JPL scientists and collaborators have detected for the first time in an individual object the kinetic Sunyaev-Zel'dovich effect, a change in the cosmic microwave background caused by its interaction with massive moving objects.  

MACS J0717.5+3745 is an extraordinarily dynamic galaxy cluster with a total mass greater than 1015 (a million billion) times the mass of the sun or more than 1,000 times the mass of our own galaxy. It appears to contain three relatively stationary subclusters (A, C, and D) and one subcluster (B) that is being drawn into the larger galaxy cluster, moving at a speed of 3,000 kilometers per second.

The galaxy cluster was observed by a team led by Sunil Golwala, professor of physics at Caltech and director of the Caltech Submillimeter Observatory (CSO) in Hawaii. Subcluster B was observed during what appears to be its first fall into MACS J0717.5+3745. Its momentum will carry it through the center of the galaxy cluster temporarily, but the strong gravitational pull of MACS J0717.5+3745 will pull subcluster B back again. Eventually, subcluster B should settle in with its stationary counterparts, subclusters A, C, and D.

Though subcluster B's behavior is dramatic, it fits neatly within the standard cosmological model. But the details of the observations of MACS J0717.5+3745 at different wavelengths were puzzling until they were analyzed in terms of a theory called the kinetic Sunyaev-Zel'dovich (SZ) effect.

In 1972, two Russian physicists, Rashid Sunyaev and Yakov Zel'dovich, predicted that we should be able to see distortions in the cosmic microwave background (CMB)—the afterglow of the Big Bang—whenever it interacts with a collection of free electrons. These free electrons are present in the intracluster medium, which is made up primarily of gas. Gas within dense clusters of galaxies is heated to such an extreme temperature, around 100 million degrees, that it no longer coheres into atoms. According to Sunyaev and Zel'dovich, the photons of the CMB should be scattered by the high-energy electrons in the intracluster medium and take on a measurable energy boost as they pass through the galaxy cluster.

This phenomenon, known as the thermal SZ effect, has been well supported by observational data since the early 1980s, so it was no surprise when MACS J0717.5+3745 showed signs of the effect. But recent observations of this galaxy cluster yielded some curious data. A team led by Golwala and Jamie Bock—also a Caltech professor of physics—observed MACS J0717.5+3745 with the CSO's Bolocam instrument, measuring microwave radiation from the cluster at two frequencies: 140 GHz and 268 GHz. Through a simple extrapolation, the 140 GHz measurement can be used to predict the 268 GHz measurement assuming the thermal SZ effect.

Yet observations of subcluster B at 268 GHz did not match those expectations. The trio of Caltech and JPL postdocs who had first proposed observations of MACS J0717.5+3745—Jack Sayers, Phil Korngut, and Tony Mroczkowski—puzzled over these images for some time. Trying to sort out the discrepancy, Korngut kept returning to subcluster B's rapid velocity relative to the rest of the cluster. Prompted by Korngut's interest, Mroczkowski decided one weekend to calculate whether the kinetic SZ effect might explain the discrepancy between the 140 GHz and 268 GHz data. To everyone's surprise, it could. In order to show this conclusively, the signals from dusty galaxies behind MACS J0717.5+3745 also had to be accounted for, which was done using data at higher frequencies from the Herschel Space Observatory analyzed by Mike Zemcov, a senior postdoctoral scholar at Caltech. The model combining the two SZ effects and the dusty galaxies was a good match to the observations.

The kinetic SZ effect, like the thermal SZ effect, is caused by the interaction of the extremely hot and energetic electrons in the gas of the intracluster medium with the CMB's photons. However, in the kinetic effect, the photons are affected not by the heat of the electrons, which gives a random, uncoordinated motion, but instead by their coherent motion as their host subcluster moves through space. The size of the effect is proportional to the electrons' speed—in this case, the speed of subcluster B.

Prior to this study of MACS J0717.5+3745, the best indication of the kinetic SZ effect came from a statistical study of a large number of galaxies and galaxy clusters that had been detected by the Atacama Cosmology Telescope and the Sloan Digital Sky Survey. This is the first time, Golwala says, "that you can point to a single object and say, 'We think we see it, right there.'"

"By using the kinetic SZ effect to measure the velocities of whole clusters relative to the expanding universe, we may be able to learn more about what causes the universe's accelerating expansion," Golwala explains. The next step in the process is the development of new, more sensitive instrumentation, including the new Multiwavelength Sub/millimeter Inductance Camera recently commissioned on the CSO.

The paper detailing these observations is titled "A Measurement of the Kinetic Sunyaev-Zel'dovich Signal Towards MACS J0717.5+3745," and appears in Astrophysical Journal. Sayers, Mroczkowski (now at the U.S. Naval Research Laboratory), Zemcov, and Korngut are the lead authors. Other authors from Caltech and JPL include Bock, Nicole Czakon (now at Academia Sinica in Taiwan), Golwala, Leonidas Moustakas, and Seth Siegel. Funding for the research was provided by the Gordon and Betty Moore Foundation, the National Aeronautics and Space Administration, the National Science Foundation, the Norris Foundation, the National Science Council of Taiwan, and the Academia Sinica Institute of Astronomy and Astrophysics.

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Stone Receives NASA Award on National Television

Edward C. Stone, the David Morrisroe Professor of Physics and vice provost for special projects at the California Institute of Technology (Caltech), has been awarded a NASA Distinguished Public Service Medal. The medal was presented to Stone by television personality Stephen Colbert on the December 3 broadcast of The Colbert Report.

Stone appeared on the program to discuss NASA's Voyager mission. Since their launch in 1977, the twin Voyager spacecraft, Voyager 1 and Voyager 2, have explored the outer planets of our solar system, greatly expanding our knowledge of Jupiter, Saturn, Uranus, and Neptune. Stone and the Voyager team recently confirmed that Voyager 1, the farthest-traveled object built by humans, had crossed into interstellar space. During his interview with Colbert, Stone answered questions about the past, present, and future of the Voyager mission.

Explaining the significance of Voyager to Colbert's audience, Stone said, "This really is a first step for our human journey beyond Earth, and beyond in fact the planets and into interstellar space, and these two spacecraft, now, will be in orbit around the center of our galaxy for billions of years."

What came at the close of the program, however, was a surprise even to Stone: Colbert drifted on stage in a spacesuit costume right out of a 1950s sci-fi movie and presented Stone with the medal.

"I was completely taken by surprise when Stephen Colbert handed me the medal," says Stone. "It's an honor for anyone to receive such an award from NASA, but to have it delivered this way was really extraordinary."

The Distinguished Public Service Medal is NASA's highest honor for a nongovernment individual. Stone was recognized "for a lifetime of extraordinary scientific achievement and outstanding leadership of space science missions, and for his exemplary sharing of the exciting results with the public," according to the award citation.

Stone joined the Caltech faculty in 1967. He became the project scientist for the Voyager mission in 1972 and has held that position to the present day. Stone served as director of the Jet Propulsion Laboratory, which is managed for NASA by Caltech, from 1991 to 2001. He is currently vice chair of the board of directors of the Thirty Meter Telescope project.

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From Spinning Black Holes to Exploding Stars: A New View of the Energetic Universe

Watson Lecture Preview

The Nuclear Spectroscopic Telescope Array, or NuSTAR, sees the high-energy X-rays emitted by the densest, hottest regions of the universe. The brainchild of Fiona Harrison, Caltech's Benjamin M. Rosen Professor of Physics and Astronomy and NuSTAR's principal investigator, the phone-booth-sized NuSTAR was launched from beneath an airplane's wing, unfolding to the length of a school bus once in orbit. Professor Harrison will describe NuSTAR's unlikely journey and share some of its remarkable results at 8:00 p.m. on Wednesday, December 4, in Caltech's Beckman Auditorium. Admission is free.

 

Q: What's "new" about NuSTAR?

NuSTAR is the first focusing high-energy X-ray telescope. X-rays can be focused by reflection, but they're so penetrating that they only reflect at very glancing angles—sort of like skipping a stone off the surface of a lake. But most of the X-rays don't interact even then, so you use "nested optics," which you can think of as a set of cones nested inside one another like Russian dolls. Each cone intercepts some of the X-ray beam. The higher the energy, the more glancing the reflecting angle is, and the more cones you need.

Other focusing telescopes, such as NASA's Chandra X-ray Observatory and the European Space Agency's X-ray Multi-Mirror Mission, observe X-rays with energies below about 10 kilo-electronvolts. NuSTAR can see up to 79 kilo-electronvolts. Chandra has four nested mirrors, each about an inch thick and set at about a one-degree angle; NuSTAR has 133 mirrors as thin as my fingernail and almost parallel to the incoming light. We developed the detector here at Caltech. It's a digital camera, but made out of a special material that stops the high-energy X-rays that would have gone straight through previous X-ray imaging detectors.

NuSTAR is hundreds of times more sensitive, and its images are 10 times crisper than its nonfocusing predecessors, which basically worked like the pinhole camera you may have used to watch a solar eclipse. So we're able to observe the universe to much greater depth and in much greater detail than has previously been possible.

 

Q: What does NuSTAR see that we wouldn't see at other wavelengths?

A whole variety of things.

Medical X-rays are about 60 kilo-electronvolts, which is in the band that we observe. They penetrate the skin but stop in the bones, casting a shadow that shows up on the film. Similarly, we can look into the hearts of galaxies with high-energy X-rays, which penetrate the clouds of dust and gas where low-energy X-rays would be absorbed. We can see supermassive black holes, or rather the X-rays emitted by the very hot stuff falling into them. We can see neutron stars, which are the collapsed cores of burned-out stars so dense that a teaspoon of neutron star would weigh more than all of humanity. We can see the remnants of dead, exploded stars.

 

Q: What is your role in all this?

A: I built a pinhole-camera-type X-ray telescope as part of my PhD work at Berkeley in the early '90s, but I needed something much more sensitive to do what I really wanted to do. So I came down to Caltech, and we began developing NuSTAR's technology for a balloon experiment called the High-Energy Focusing Telescope, or HEFT. HEFT flew in 2005 and was so successful that we submitted a proposal to NASA's Small Explorer program to build a space version. As the principal investigator, I was responsible for putting the team together that proposed NuSTAR to NASA, and for overseeing the construction and launch. Now I lead the science team, which decides what to look at and analyzes all the data. Our primary mission ends in 2014, so right now I'm starting to write a proposal to extend the mission for another two years as a guest-investigator program open to anyone anywhere in the world.

I hope NuSTAR keeps me busy for another 10 years or more. There are no expendables such as cryogenic coolant, so it's a matter of how long the orbit lasts. We do experience atmospheric drag, so NuSTAR will eventually reenter and burn up. Either that, or something will break. As a small, inexpensive mission, we don't have redundant systems. If something breaks, there's no backup to switch over to.

 

Named for the late Caltech professor Earnest C. Watson, who founded the series in 1922, the Watson Lectures present Caltech and JPL researchers describing their work to the public. Many past Watson Lectures are available online at Caltech's iTunes U site.

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Douglas Smith
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Peering Through the Intergalactic Dust

Caltech Builds a New Submillimeter Telescope in the Atacama Desert

Where do you go to look at the stars? Away from city lights, certainly. But if you're serious about peering far out into space, to the observable edges of our universe, at submillimeter wavelengths, you have to do a little better than that. You have to go farther and higher, up to where the atmosphere is thin. And if you want to look at the stars for more than a few nights a year, you also need some place that is very, very dry. Clouds, of course, obstruct the view of stars and galaxies, but even water vapor in the atmosphere can interfere with incoming electromagnetic radiation.

One of the most hospitable places for astronomy is also among the least hospitable for human life: the Atacama Desert in northern Chile, at high elevations. The Atacama is the driest desert on Earth, receiving perhaps a half an inch of rain each year (and in some locations, none at all). Because the region has been arid for so long, its mountain peaks rarely have glaciers or permanent snow coverage. The desert extends from the sea up toward the highest western ridge of the Andes. Even at the coast, the human population is sparse. But the very best conditions for submillimeter astronomy are found higher up.

The summit of Cerro Chajnantor, at an altitude of 5,617 meters (nearly 18,500 feet), is the proposed site for a new telescope known only by an acronym: CCAT. CCAT is a 25-meter telescope that observes electromagnetic radiation at wavelengths a little shorter than a millimeter—that is, wavelengths a thousand times longer than optical light. Because water vapor so strongly absorbs submillimeter-wave radiation, the ultradry Atacama Desert has been the go-to location for submillimeter telescopes for several decades. Indeed, from its perch on Cerro Chajnantor, the future CCAT will look down on a veritable forest of telescopes on the plateau some 600 meters below. To the northwest, the Atacama Pathfinder Experiment (APEX) and Atacama Cosmology Telescope (ACT) are visible; to the east are the Japanese Atacama Submillimeter Telescope Experiment (ASTE) and NANTEN telescopes; immediately below are the 66 telescopes in the Atacama Large Millimeter/submillimeter Array (ALMA).

So why truck up an extra 600 meters above the plateau in a cold, uninviting landscape over a rough dirt road to build CCAT? Surprisingly, the even thinner, drier air at the summit buys scientists a 1.4-fold increase in sensitivity over telescopes located on the plateau. It is "the driest high-altitude site to which one can drive a truck," says Riccardo Giovanelli, project director for CCAT.

The electromagnetic radiation that reaches us on Earth in the visible range of the light spectrum has always fascinated humans, because we can see it with our own eyes, or with the enhanced eye of an optical telescope. But electromagnetic radiation that comes to Earth at longer wavelengths has its own stories to tell about the universe. Most of the radiation emitted by stars falls in the ultraviolet (UV) and optical range, and can be detected by a traditional optical telescope (provided the telescope is sensitive enough). But in dusty clouds, where stars most often form, newborn stars are obscured and become invisible to an optical telescope. Fortunately, however, this UV and optical radiation from the new stars heats up the dust. The dust absorbs the star's UV and optical radiation, and reemits it into the universe at longer submillimeter wavelengths. By measuring the submillimeter radiation from the clouds, astronomers can learn about the stars that are hidden within.

There is widespread agreement in the scientific community that it is urgent to move forward with CCAT. In its 2010 Astronomy and Astrophysics Decadal Survey, the National Research Council of the National Academy of Sciences urged CCAT "to progress promptly to the next step in its development because of its strong science case … and its readiness." CCAT is drawing toward the close of its design phase. Construction should begin in 2014; first light—that is, the first scientific use of the instrument—is scheduled for 2019.

Lead engineer on the CCAT project is Stephen Padin, senior research associate in astrophysics at Caltech. According to Tom Soifer, chair of Caltech's Division of Physics, Mathematics, and Astronomy, Padin is "the only person on Earth with the experience and brilliance to build CCAT." During Padin's decades-long career as a vagabond telescope builder, he has helped to design and construct Antarctica's South Pole Telescope and the radio dishes that comprise the Owens Valley Radio Observatory. But the Atacama Desert, where Padin engineered the Cosmic Background Imager (CBI) telescope for Caltech 20 years ago, has a special allure for him. "It looks just like pictures of the martian surface," Padin says, "except the sky is a deep blue above the desert, while it is orange on Mars." Padin remembers one night on-site in Chile looking through a 6-inch refracting telescope while taking some measurements to adjust the CBI's pointing mechanism: "The view was astounding. Sharp, bright, and with a snap that no picture on a page or computer screen could ever hope to achieve."

At 25 meters in diameter, the CCAT telescope is substantially larger than both the next-largest submillimeter telescope, the 15-meter James Clerk Maxwell Telescope (JCMT) atop Hawaii's Mauna Kea, and the Herschel Space Observatory, which is a mere 3.5 meters in diameter. Like JCMT, CCAT will have a segmented mirror constructed of machined aluminum, a material that is lightweight and very reflective. The structure supporting the mirror will be built of carbon-fiber-reinforced plastic, which is light, stiff, and stable. Submillimeter telescopes are at a bit of an advantage over optical telescopes when it comes to procuring the necessary materials. Because telescopes like CCAT are designed to detect longer wavelengths of electromagnetic radiation, they can tolerate a somewhat rougher surface than optical telescopes. Optical telescopes must have a glass mirror and a steel structure to support that weight, while submillimeter telescopes can be constructed of lighter, less expensive materials.

To construct the mirror, the aluminum segments must be carefully machined and then accurately mounted on the support structure. Then the telescope must be installed on Cerro Chajnantor, which, at present, can only be reached via a road that is narrow, steep, and winding. To get to the top, says Padin, "you'll have to stop and roll a few boulders out of the way." Although the existing road will be widened before CCAT is installed, it will never be paved. (However, Padin notes, the Cerro Chajnantor road will be "a considerable improvement over access to Mount Wilson when the 60-inch reflecting telescope was built. Many of those parts were hauled up by mule teams.")

"The main issues for the CCAT site are that it's remote, and people can't breathe up there," Padin says. "Remote is always a problem for projects in astronomy, because you've got to get a lot of high-technology stuff to the middle of nowhere and then make it work. But in this case, you also have to factor in the effects of the altitude. People don't think very well at 18,500 feet." Indeed, the site is halfway to the altitude of a typical passenger airplane, and that means workers will be breathing in only about half the oxygen they would take in at sea level. To offset the effects of the altitude, workers will be required to use supplementary oxygen.

Leveling the site and producing an enclosure for CCAT will be handled by local Chilean companies, while scientific instruments and the pieces of the telescope itself—approximately 500 metric tons of equipment being developed and built all over the world—will be shipped in by sea. Then the entire telescope will be put together "at lower altitude," Padin explains, "where the scientists can think." At this stage, the team will verify that all of the components fit together properly and fix any minor problems. "It's embarrassing if you get on top of the mountain with a big pile of bits that don't fit," Padin says. After this test assembly, CCAT will be dismantled and trucked up to the summit of Cerro Chajnantor where it will be assembled for a second time.

Following construction, CCAT will be a fully automated observatory. In principle, says Padin, "you'll be able to sit at home with your laptop and drive the telescope." Except when problems arise or maintenance is required, the site will be uninhabited when CCAT is making observations. Padin laments the loss of "one of the big attractions for astronomy: traveling to exotic places and doing strange things in the middle of the night." Still, he admits, going to a mountain in the Atacama Desert "is fun the first time," but it becomes "less appealing as time goes on."

By peering into the submillimeter, CCAT will give us new eyes on the universe and help to resolve some pressing questions about star and galaxy formation. As Padin explains, "Astronomy is in an interesting position at the moment. We know a lot about the nearby stuff. We've spent hundreds of years looking at that at optical wavelengths. And now we actually know quite a bit about cosmology from measuring the microwave background left behind by the Big Bang. We know less about what happened in the middle, about the first stars turning on, the first galaxies forming. What happened between the smooth Big Bang and the very lumpy structure that we see now? This is the question that the next generation of telescopes, including CCAT, promises to address."

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Cynthia Eller
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Himiko and the Cosmic Dawn

Hubble and ALMA Observations Probe the Primitive Nature of a Distant "Space Blob"

The Subaru Telescope, an 8.2-meter telescope operated by the National Astronomical Observatory of Japan, has been combing the night sky since 1999. Located at the Mauna Kea Observatories in Hawaii, the telescope has been systematically surveying each degree of space, whether it looks promising or not, in search of objects worthy of further investigation. One of the most fascinating objects to emerge from the Subaru Telescope's wide-field survey—Himiko—was discovered in 2009. Himiko, a "space blob" named after a legendary queen from ancient Japan, is a simply enormous galaxy, with a hot glowing gaseous halo extending over 55,000 light-years. Not only is Himiko very large, it is extraordinarily distant, seen at a time approximately 800 million years after the Big Bang, when the universe was only 6 percent of its present size and stars and galaxies were just beginning to form.

How could such an early galaxy have sufficient energy to power such a vast glowing gas cloud? In search of the answer to this question, Richard Ellis, the Steele Family Professor of Astronomy at Caltech, together with colleagues from the University of Tokyo and the Harvard-Smithsonian Center for Astrophysics, undertook an exploration of Himiko using the combined resources of the Hubble Space Telescope and the new Atacama Large Millimeter/submillimeter Array (ALMA) in Chile's Atacama Desert. The data collected through these observations answered the initial question about the source of energy powering Himiko, but revealed some puzzling data as well.

The Hubble images, receiving optical and ultraviolet light, reveal three stellar clumps covering a space of 20,000 light-years. Each clump is the size of a typical luminous galaxy dating to the epoch of Himiko. Together, the clumps achieve a prodigious rate of star formation, equivalent to about one hundred solar masses per year. This is more than sufficient to explain the existence of Himiko and its gaseous halo. The observation of the three stellar clumps is exciting in itself, as it means that Himiko is a "triple merger," which, according to Ellis, is "a remarkably rare event."

But a surprising anomaly emerged when Himiko was observed by ALMA. Although the giant gas cloud was bustling with energy at ultraviolet and optical frequencies, it was comparatively sleepy in the submillimeter and radio ranges that ALMA detects. Ordinarily, intense star formation creates dust clouds that are composed of elements such as carbon, oxygen, and silicon, which are heavy in comparison to the hydrogen and helium of the early universe. When these dust clouds are heated up by the ultraviolet light emitted by the developing stars, the dust reradiates the ultraviolet light out into the universe at radio wavelengths. But ALMA did not receive significant radio signals from Himiko, suggesting that heavier elements are not present. Also missing was the spectral signature associated with the emission of gaseous carbon, something also common in galaxies with intense star formation.

Both of these nondetections—of substantial radio waves and of gaseous carbon—are perplexing since carbon is ordinarily rapidly synthesized in young stars. Indeed, carbon emission has heretofore been recommended as a tracer of star formation in distant galaxies. But, as Ellis and his fellow astronomers found, Himiko does not contain the dust clouds of heavier elements that astronomers find in typical energetic galaxies. Instead its interstellar gas is composed of hydrogen and helium—primitive materials formed in the Big Bang itself.

Ellis and his fellow astronomers did not come to this conclusion quickly. They first carefully ruled out several other possible explanations for Himiko, including that the giant blob is being created by the magnification of a foreground object by a phenomenon known as gravitational lensing, or is being powered by a massive black hole at its center. Ultimately, the team concluded that Himiko is most likely a primordial galaxy caught in the moment of its formation between 400 million to 1 billion years after the Big Bang, a period astronomers term the cosmic dawn.

"Astronomers are usually excited when a signal from an object is detected," Ellis says, "but in this case it's the absence of a signal from heavy elements that is the most exciting result!"

The paper reporting the results of this research, titled "An Intensely Star-Forming Galaxy at Z ~ 7 with Low Dust and Metal Content Revealed by Deep ALMA and HST Observations," will be published in the December 1, 2013, issue of the Astrophysical Journal. The work was funded by NASA through a grant from the Space Telescope Science Institute, the World Premier International Research Center Initiative (WPI Initiative), and the Japan Society for the Promotion of Science (JSPS).

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Cynthia Eller
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