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  • richardmitnick 1:24 pm on March 16, 2017 Permalink | Reply
    Tags: , , , , , , U Toronto Dragonfly Telescope Array, When the Neighborhood Dwarf Galaxies were Kids   

    From astrobites: “When the Neighborhood Dwarf Galaxies were Kids’ 

    Astrobites bloc


    Title: Local Group Ultra-Faint Dwarf Galaxies in the Reionization Era
    Authors: D. R. Weisz, M. Boylan-Kolchin
    First Author’s Institution: Department of Astronomy, University of California Berkeley, Berkeley, CA
    No image credit
    Status: Submitted to MNRAS, [open access]

    The heavens bespeak a dark and quiet night, glinting here and there with distant stars and yet more distant galaxies. But in ages past, long before the birth of our stalwart Sun, before even the supernovae that spewed the calcium in our bones and the iron in our blood into the gas that formed the Sun and the Solar System, there was darkness. The cosmic dark ages reigned for nearly a million years before the first stars blinked blearily on.

    Then suddenly there came an age of light. We’re not entirely sure what exactly lit up the universe, but among the suspects are the first galaxies. Once practically invisible, they were lit aflame as the first stars began to burn hot and bright within them. They generated copious amounts of ultra-violet (UV) light, energetic enough to ionize the hydrogen in the universe. So much UV flux was generated that nearly all the hydrogen in the universe was ionized, leaving the universe clear and transparent and allowing us the majestic views of faraway galaxies that we take for granted today.

    Figure 1. The role of small galaxies like the Milky Way’s newly discovered ultra-faint galaxies could have had in reionizing the universe. The top panel shows the number density of galaxies as a function of how bright they were in the ultra-violet (MUV), what we call the Salpeter function. The colors denote how the numbers changed with time; purple (z ~ 8) denotes when reionization occurred, and the lighter colors denote the subsequent evolution after reionization. Far more faint galaxies (less negative MUV) exist compared to brighter galaxies. Together, they produced most of the UV flux during reionization, as shown in the middle and bottom panels: the middle panel shows the density of UV photons (which is clearly highest at the faint end), and the bottom panel shows the cumulative fraction of the flux that galaxies brighter than a given MUV were generating. As much as 50-80% of the UV flux that reionized the universe may have come from galaxies fainter than MUV ~ -10! Figure taken from today’s paper.

    The authors of today’s paper investigate what role the newly discovered ultra-faint dwarf galaxies orbiting our Milky Way could have had during this epoch of reionization. For it turns out that our most careful galaxy counts—which we’ve codified into what we now call the Schechter function (see Figure 1)—tell us that the universe swarms with dwarf galaxies, which are at least a thousand times less massive than the more familiar grand spirals such as the Milky Way. The Milky Way itself is thought to be surrounded by several hundreds, if not thousands, of such galaxies. Dwarf galaxies are so numerous that together, they may have been able to provide much of the UV photons required. It was an age in which the smallest galaxies ruled the ultra-violet skies.

    Dwarf Galaxies with Messier 101 Allison Merritt Dragonfly Telephoto Array

    U Toronta Dragon Fly Telescope Array

    We don’t know for sure if dwarf galaxies can solve the mystery of reionization. The problem is that it’s extremely difficult to peer into the universe’s distant past, and literally impossible to observe the faint dwarfs that existed then. Our best observations hint that there were many more dwarfs in the past than in the present, before they were torn apart and cannibalized by larger galaxies.

    To work around these uncertainties, the authors did something simple. They worked out when the stars in the Milky Way’s ultra-faint dwarfs formed to determine how much UV light they’d give off during reionization. They then asked: If the Schechter function was valid for dwarfs as dim as the Milky Way’s faintest dwarfs used to be, how much UV light would they have produced? They found that dwarfs could have generated as much as 50-80% of the UV photons needed to reionize the universe.

    There’s hints, however, that such a simple extrapolation of the Schechter function to ultra-faint galaxies overestimates the number of bright UV-emitting dwarfs. The Schechter function predicts that we should see as many as ten times as many bright dwarfs around the Milky Way than we actually do. And it’s becoming clear that the smallest galaxies have trouble producing UV-generating stars. This would cause the Schechter function to “turn over” (see Figure 2) or predict fewer bright dwarfs (and hordes of small, dark galaxies). The authors show that the estimated reduction in bright dwarfs seen in simulations lowers the UV flux we should expect from small galaxies to about 10%.

    Although we haven’t yet gotten to the bottom of how large a role dwarf galaxies played in the ionization of the universe, it’s clear that the yet unobservable number of UV-bright dwarfs matters greatly in understanding how the history of the universe unfolded. The upcoming James Webb Space Telescope has the ability to detect galaxies from the epoch of reionization that are almost 100x fainter—still far short of the 10,000x increase in sensitivity we need to see the faint UV galaxies that preoccupied today’s authors. It’ll be a big step forward, but we’ll still have to hunt for other clues as to the true numbers of dwarf galaxies during reionization.

    Figure 2. How a reduction in the number of ultra-faint dwarf galaxies can reduce their contribution to the reionization of the universe. The top panel shows different guesses as to the number density of galaxies of a given UV brightness. In black is the traditional Salpeter function, which predicts many faint UV galaxies, while the orange and purple curves are based on simulations that show a “turn-over” or reduction in the number of faint UV galaxies. The bottom panel shows that if there are just a few UV-faint galaxies, then they contribute only ~10% of the UV flux that reionized the universe. Figure taken from today’s paper.

    See the full article here .

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    What do we do?

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    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

  • richardmitnick 10:50 am on January 28, 2016 Permalink | Reply
    Tags: , , How to Discover a Galaxy with a Telephoto Lens, , U Toronto Dragonfly Telescope Array   

    From Nautilus: “How to Discover a Galaxy with a Telephoto Lens” 



    January 28, 2016
    Patchen Barss

    U Toronto Dunlap Dragonfly telescope Array
    Dragonfly telescope at Dunlap Institute, U Toronto

    Like countless so-crazy-it-just-might-work schemes, this one began with a gripe session. In the fall of 2011, Roberto Abraham and Pieter van Dokkum were commiserating at a Nepalese restaurant in Toronto. Over curry and rice—and a generous quantity of beer—the old friends bemoaned a problem they’d discussed many times before.

    As observational cosmologists, they shared a professional interest in how galaxies are born and evolve. The leading theory, known as hierarchical galaxy formation, describes this growth as a long scaling up, from little to big, simple to complex. In the beginning, just a few thousand years after the Big Bang, almost all mass was dark matter—that mysterious, unseen counterpart to ordinary, luminous matter. But dark matter didn’t spread evenly across the infant universe, and soon denser pockets began to clump together, condensing into roughly spherical bundles under gravity’s pull. As these “dark matter halos” grew larger and more compact, gases gathered in their cores, fueling stars—the first galaxies. Over billions of years, galaxies collided and merged into bigger and bigger systems, eventually creating brilliant cosmic behemoths like our own Milky Way.

    Testing this theory, however, wasn’t easy. Modelers were continually spitting out predictions about galaxy structure and behavior that, if observed in the actual universe, would refine the story and give it credence. But more often than not, astronomers like Abraham and van Dokkum found they could neither support nor refute the models using current telescopes. “We were frustrated because we couldn’t push the existing technology further,” says van Dokkum, a professor at Yale University.

    They were also frustrated with how cumbersome astronomy had become: Modern astronomical projects are typically large-scale affairs, requiring a small fortune, a mountain of paperwork, and plenty of patience. “You have to envision ways to get $10 million and put a team together, and even then, you only know if things will come to fruition a decade later,” says Abraham, a professor at the University of Toronto.

    There had to be a better approach. As their conversation deepened, he and van Dokkum mused about whether a couple of plucky cosmologists could strike out on their own. They fantasized about finding a quick-and-dirty way to put the theory of hierarchical galaxy formation to the test. But how?

    Then gradually, unexpectedly, an answer presented itself. According to one long-standing prediction, big galaxies like the Milky Way should sit in vast, disorderly fields of debris—ejected stars, half-eaten halos, and other remnants of the violent collisions that created them. Computer models show these galaxies surrounded by wispy knots, bulges, and streams of matter. Hundreds to thousands of faint, dark-matter-rich dwarf galaxies whirl around them. As Abraham has put it, “Every galaxy should look like a squashed bug.”

    Seen through current telescopes, though, galaxies appear smooth and symmetrical—classical spirals and ellipses. This might suggest that cosmologists’ theory about galactic evolution is wrong. But more likely, Abraham and van Dokkum surmised, conventional telescopes simply can’t pick out the dim, diffuse rubble swirling beyond a galaxy’s bright center.

    The problem isn’t a matter of telescope size. Larger and larger mirrors have allowed astronomers to peer deeper and deeper into space and time, descrying extraordinarily faint pinpoints of light from the early universe. But when researchers try to survey diffuse matter spread across a large swatch of sky, such as the halo around a nearby galaxy, they run into trouble. Tiny irregularities in a mirror’s reflective surface scatter the incoming light, polluting the image with ghosts and other artifacts that obscure the real data.

    Suddenly, swallowing another swig of beer, van Dokkum realized he might know of a way out of this predicament. He’d made a hobby of wildlife photography (he recently published a collection of photos of dragonflies), and kept up with camera trends. “I had heard about these awesome new telephoto lenses,” he says. The Japanese optics corporation Canon had started producing high-end lenses coated with a proprietary film of nano-sized cones. By deflecting errant light away from a camera’s detector, Canon claimed, the cones effectively eliminated the effects of scattering. Photographers could now get crisp, true-to-life images—no more ghosts or flares.

    Van Dokkum wondered aloud: What would happen if he and Abraham turned lenses like these on the cosmos? Would they finally detect the delicate, shadowy structures surrounding galaxies that cosmologists had long been searching for?

    With a 16-centimeter diameter, one Canon lens wouldn’t reveal much: It would take weeks of nightly exposures just to collect enough light to make out the kind of dim objects the cosmologists hoped to see. And that was assuming perfect weather and no technical hiccups. But what if they added more lenses? By imaging galaxies through multiple lenses simultaneously, like a dragonfly’s compound eye, they could capture fainter structures in less time, while also correcting for errors.

    “For me, the whole conversation was somehow theoretical,” van Dokkum recalls. “But Bob said, ‘You know, why don’t we just do it? Like, actually build it?’ ”

    They would call their creation Dragonfly.

    Within a few months, Abraham and van Dokkum had scraped together about $15,000 in research funds to buy one of the new Canon lenses and accompanying equipment. In March of 2012, they drove it up to the Mont-Mégantic Dark Sky Preserve, in Quebec, to test it out: Would the coating of nanocones prove as revolutionary as Canon claimed?

    In a snowy parking lot filled with amateur stargazers, they attached the lens to a camera, mounted it on a tripod, and trained the diminutive telescope on a spiral galaxy known as M51. First observed in the late 1700s, M51 has been intensely studied and photographed for centuries. But after a two-hour exposure, Canon’s lens captured a sight that scientists had only gleaned hints of before: Extending far beyond M51’s bright central spiral was a distinct halo of diffuse matter. “We quickly realized that the lens really was as outstanding as we had hoped,” van Dokkum says.

    It took them another few months to raise the money for two more lenses and other off-the-shelf parts to build Dragonfly. They paired each lens with a digital camera and focuser, and wired everything to a Mac mini. (To minimize reboots, each lens now operates via its own thumb drive-sized controller, which communicates wirelessly with a master computer.) They encased the lenses in protective metal cylinders, which they then bolted together on a custom-made mount, so that all of Dragonfly’s eyes would point at the same spot in the sky. Abraham wrote software that would combine the three nearly identical snapshots into a single image.

    In September 2012, they shipped Dragonfly to a telescope-hosting site in southern New Mexico, where they could count on clear skies most nights. “We literally Fed-Exed our equipment, booked flights, and set it up before that month was out,” van Dokkum says.

    Back at their home universities, they could control Dragonfly over the Internet, at their whim. The ease and freedom was exhilarating. “If we decide that tonight we want to observe Saturn, we can do it,” van Dokkum says. “That amount of creativity and flexibility is incredibly rare [in astronomy].”

    By 2013, they had upgraded Dragonfly to eight lenses, and in 2014, they published their first significant discovery. With Allison Merritt, a graduate student at Yale, they imaged a large spiral galaxy known as M101, or the Pinwheel Galaxy. In the field around it, they identified seven dwarf galaxies that no one had seen before. But when they analyzed the data, they found that only three of these dwarfs were orbiting M101. Models predicted hundreds. Where were the rest?

    It’s possible that many of M101’s satellites are too dim for Dragonfly to see. There may even be “naked” halos orbiting the galaxy that have no stars at all. But Abraham and van Dokkum say the paucity of brighter dwarfs is strange. “If Dragonfly fails to find these satellites [around other galaxies], then either the theory of hierarchical galaxy formation is totally wrong, or there’s some physics that prevents stars from forming or tears them up,” Abraham says. “I suspect it’s the latter—nature’s got surprising ways of getting rid of stars or never allowing them to form in the first place.”

    In addition to dwarf satellites, the researchers expected to see a halo of rubble around M101. Dragonfly, they knew, was sensitive enough to detect it. But the telescope revealed nothing—the halo was conspicuously absent. What do the rabble-rousing astronomers make of that fact? “Not much,” van Dokkum says. “You can’t rule out a whole class of theories based on one object.”

    The findings from M101 convinced them to begin a systematic survey. They got a grant to image 20 to 30 galaxies in three years, and recruited another graduate student, Jielai Zhang, at the University of Toronto. (They expect to publish the first results by 2017.)

    Meanwhile, Dragonfly grew, to 10 lenses, then 24, and soon 48 (plus two guiding lenses). “At 50 [lenses], we’re effectively the world’s largest working refractor telescope,” Abraham says. The upgrades have drastically sped up the time it takes to produce an image, from weeks to hours. And although the telescope is still technically a prototype, it is already expanding the catalog of objects in the known universe.

    Recently, for example, Abraham and van Dokkum took a break from the galaxy survey to—why not!—image the Coma Cluster, a crowded agglomeration of galaxies 300 million light-years from Earth. To the scientists’ amazement, the portrait revealed dozens of massive galaxies that were curiously dim. As big as the Milky Way, these “ultra-diffuse” galaxies emit only about a thousandth of its light.

    Current models say that such galaxies shouldn’t exist. But here they were, smack dab in the teeming, crash-happy Coma Cluster. “They must be held together by a lot of dark matter,” van Dokkum says. “Otherwise they would just be ripped apart very quickly.”

    Inspired by this finding, Jin Koda, an astronomer at Stony Brook University, in New York, and his colleagues pored over archival Coma images taken by the powerful [NAOJ]Subaru telescope atop Mauna Kea, in Hawaii.

    NAOJ Subaru Telescope
    NAOJ Subaru Telescope interior

    Using the Dragonfly data as a guide, they found hundreds more examples of ultra-diffuse galaxies that had been previously overlooked or dismissed as artifacts. “Everybody knew large diffuse galaxies don’t exist,” van Dokkum says. “So they never thought to look for them.”

    In Abraham’s view, Dragonfly is a “sort of pathfinder” to deeper research. “This little telescope is really good at finding these hard-to-detect things, but to really understand them, you need a big telescope in Hawaii, or in space.” Scattering may prevent large reflectors from revealing diffuse structures like halos and dwarf galaxies. But once Dragonfly spots them, astronomers can then use these big mirrors to zoom in on a particular object, allowing them to study it in much greater detail.

    Dragonfly has made Abraham and van Dokkum minor celebrities among hobbyists and professional astronomers alike. Their peers applaud their ingenuity and early success. “Dragonfly is the latest breakthrough in unlocking the diffuse universe,” says Joss Bland-Hawthorn, Director of the Sydney Institute for Astronomy, in Australia. He also appreciates how Dragonfly’s inventors managed to escape the bureaucratic burdens of doing cosmology. “There’s nothing more thrilling than being on the quest for something new, and having your own destiny in your hands,” he says.

    Avi Loeb, an astronomer at Harvard University, agrees. He credits Dragonfly for the publication of one of his group’s most recent theoretical papers. In early 2015, he and his co-authors had developed evolutionary models predicting glowing gas emissions “near the outskirts” of galaxy clusters. According to their calculations, however, these emissions were too dim to observe using existing telescopes. Without means to verify their prediction, they had decided it wasn’t worth publishing.

    Then, as luck would have it, they attended a colloquium at Harvard University, where Abraham presented some of the first findings from Dragonfly. “We learned that Dragonfly could detect the exact glow we predicted in our equations,” Loeb says. Thrilled, they submitted the paper, which was published this month.

    Abraham and van Dokkum can’t yet say how big Dragonfly will get or how much it will be able to see. So far, with up to 24 lenses (they’re still finishing up the 50-lens upgrade), they have been able to pick out objects about a tenth as diffuse as conventional telescopes can clearly resolve. In theory, more lenses should reveal dimmer stuff. But there might be a limit: Factors such as the refractive index of Dragonfly’s lenses and the presence of faint cosmic light pollution, known as galactic cirrus, may put a hard cap on the telescope’s capabilities.

    “Whether we can go beyond 50 [lenses] is unclear,” van Dokkum says. “It also depends a bit on how big we want to go. If we want 500 lenses, then we’d need a much bigger operation, and it would start to take over our lives. And then we’d have to look around for a new fun project.”

    See the full article here .

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    Welcome to Nautilus. We are delighted you joined us. We are here to tell you about science and its endless connections to our lives. Each month we choose a single topic. And each Thursday we publish a new chapter on that topic online. Each issue combines the sciences, culture and philosophy into a single story told by the world’s leading thinkers and writers. We follow the story wherever it leads us. Read our essays, investigative reports, and blogs. Fiction, too. Take in our games, videos, and graphic stories. Stop in for a minute, or an hour. Nautilus lets science spill over its usual borders. We are science, connected.

  • richardmitnick 9:29 am on March 1, 2015 Permalink | Reply
    Tags: , , , U Toronto Dragonfly Telescope Array   

    From S&S: “Dark Galaxies Discovered in Coma Cluster” 

    Sky and Telescope

    Sky and Telescope News

    November 19, 2014
    Monica Young

    Coma Cluster
    Adam Block / Mount Lemmon SkyCenter / University of Arizona

    The Coma Cluster, visible in the evening skies of spring and summer, reveals its jewel box to large backyard telescopes: several thousand galaxies sardine-packed into a space only 20 million light-years across.

    But there’s more to the Coma Cluster than meets the eye — or the backyard telescope.

    Pieter van Dokkum (Yale University) and colleagues took a unique look at Coma through the Dragonfly Telephoto Array, eight Canon telephoto lenses coupled to CCD cameras. The Dragonfly is designed to find faint, fuzzy blobs, but what its images revealed surprised the team.

    U Toronto Dunlap Dragonfly telescope Array
    The Dragonfly Telephoto Array currently consists of ten Canon telephoto lenses coupled to CCD cameras. (The paper used eight lens/CCD pairings.) The array is designed to image low surface brightness objects. Dunlap Institute for Astronomy & Astrophysics / University of Toronto

    On Coma’s outskirts lurk 47 galaxies similar in size to the Milky Way — but with 1,000 times fewer stars. To survive in crowded Coma, these dark galaxies must contain 98% dark matter to hold themselves together, much higher than the fraction in the universe at large (83%).

    Hubble imaging picked up one of the dark galaxies serendipitously. The galaxy’s smattering of red stars is barely visible against the backdrop.
    Pieter van Dokkum & others

    NASA Hubble Telescope

    The galaxies’ size depends on their distance, so to make sure this result wasn’t just a trick of perspective, van Dokkum and colleagues had to make sure these galaxies really belonged to the Coma cluster, more than 300 million light-years away. If they turned out to live nearby, the galaxies’ size would be akin to regular ol’ dwarf galaxies.

    Determining cluster membership was a challenge because the objects are far too faint to study in the usual ways, such as taking a spectrum to determine their distance. Nonetheless, “van Dokkum and his co-authors make quite a convincing case,” says Mark den Brok (University of Utah).

    The authors initially expected the galaxies to be distributed randomly, as they would be if they lay in the foreground near the Milky Way. Instead, the galaxies cluster around the center of the image in the cluster’s periphery. The discovery of a serendipitous Hubble image of one of the galaxies strengthened the team’s case, den Brok says, definitively showing that it doesn’t have the traits of a nearby dwarf galaxy.

    Starless Galaxies

    Somehow these weirdly faint galaxies have lost their stars — or they never had many stars in the first place. Van Dokkum and colleagues suggest that these may be “failed” galaxies, having forfeited most of their star-building gas after hosting a first generation of stars.

    Simulations that track the evolution of large-scale structure suggest that even normal galaxies start out with three times more star-building material than they develop into stars. So whatever process works to limit star formation in normal galaxies is working particularly well in these dark matter-rich galaxies.

    “Our simulations have shown that one way to limit star formation so drastically is to use the energy stars produce when they blow up as supernovae,” says Greg Stinson (Max Planck Institute for Astronomy, Germany). “It turns out that this disruption leads directly to galaxies that look like the ones van Dokkum is seeing.”

    “I was actually very much relieved to see Prof. van Dokkum’s paper,” Stinson adds. Dark matter simulations have been producing galaxies with exactly the size and matter distribution that van Dokkum’s team observed, but such galaxies are naturally difficult to observe.

    It’s ironic that dark matter-rich galaxies were discovered in Coma, the birthplace of dark matter theory. Observations of the same cluster in 1933 helped Fritz Zwicky (Caltech) first conceive of the invisible matter that shapes the large-scale structure of the universe. Now ever-deeper observations continue to help astronomers understand dark matter’s role in galaxy evolution.

    See the full article here.

    Another view of the Coma Cluster

    A Sloan Digital Sky Survey/Spitzer Space Telescope mosaic of the Coma Cluster in long-wavelength infrared (red), short-wavelength infrared (green), and visible light. The many faint green smudges are dwarf galaxies in the cluster.
    Credit: NASA/JPL-Caltech/GSFC/SDSS

    SDSS Telescope
    SDSS telescope

    NASA Spitzer Telescope

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    About Sky & Telescope

    Sky & Telescope magazine, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    A Brief History of Sky & Telescope

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    The Telescope

    Meanwhile, The Telescope first appeared as a quarterly magazine in March 1931 under the editorship of Harlan Stetson, director of the Perkins Observatory in Ohio. It featured popular articles about contemporary research written by professional astronomers. In 1934 Stetson moved to Cambridge, Massachusetts, and brought the magazine with him. Publishing duties were assumed by the Harvard College Observatory (HCO), and The Telescope became bimonthly.

    A New Beginning

    The first issue of the merged Sky & Telescope came out in November 1941, just one month before the bombing of Pearl Harbor.

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