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  • richardmitnick 10:45 am on December 6, 2018 Permalink | Reply
    Tags: , , , , , , Keck Cosmic Web Imager, NASA/ESA Cosmic Origins Spectrograph, , The ecosystem that controls a galaxy’s future is coming into focus   

    From Science News: “The ecosystem that controls a galaxy’s future is coming into focus” 

    From Science News

    July 12, 2018
    Lisa Grossman

    The circumgalactic medium has been hard to observe, but new tools now make it possible.

    COSMIC CLOAK Whirls of cold and hot gas billow in this simulation of a circumgalactic medium surrounding a galaxy. With new tools and simulations, researchers have learned that the CGM helps a galaxy recycle its materials. M.S. Peeples et al/FOGGIE Project

    There’s more to a galaxy than meets the eye. Galaxies’ bright stars seem to spiral serenely against the dark backdrop of space. But a more careful look reveals a whole lot of mayhem.

    “Galaxies are just like you and me,” Jessica Werk, an astronomer at the University of Washington in Seattle, said in January at a meeting of the American Astronomical Society. “They live their lives in a constant state of turmoil.”

    Much of that turmoil takes place in a huge, complicated setting called the circumgalactic medium, or CGM. This vast, roiling cloud of dust and gas is a galaxy’s fuel source, waste dump and recycling center all in one [Annual Review of Astronomy and Astrophysics]. Astronomers think the answers to some of the most pressing galactic mysteries — how galaxies keep forming new stars for billions of years, why star formation abruptly stops — are hidden in a galaxy’s enveloping CGM.

    “To understand the galaxies, you have to understand the ecosystem that they’re in,” says astronomer Molly Peeples of the Space Telescope Science Institute in Baltimore.

    Yet this galactic atmosphere is so diffuse that it’s invisible — a liter of CGM contains just a single atom. It has taken almost 60 years and an upgrade to the Hubble Space Telescope just to begin probing distant CGMs and figuring out how their constant churning can make or break galaxies.

    “Only recently have we been able to really, truly, observationally characterize the relationship between this gaseous cycle and the properties of the galaxy itself,” Werk says.

    Armed with the first extragalactic census, astronomers are now piecing together how a CGM controls its galaxy’s life and death. And new theoretical studies hint that galaxies’ stars would be arranged very differently without a medium’s frenetic flows. Plus, new observations show that some CGMs are surprisingly lumpy [Nature]. A better understanding of CGMs, enabled by new telescopes and computer simulations, could change how scientists think about everything from galaxy collisions to the origins of our own atoms.

    “The CGM is the part of the iceberg that’s under the water,” says astrophysicist Kevin Schawinski of ETH Zurich, who studies the more conventional parts of galaxies. “We now have good measurements where we’re sure it’s important.”

    Frenetic fog

    Researchers use a bright source of background light, like a quasar, to learn about a galaxy’s circumgalactic medium, a diffuse cloud of gas and metals (pink in the illustration) surrounding a galaxy. Gas is recycled between the galaxy and the CGM.

    Sources: J. Tumlinson, M.S. Peeples and J.K. Werk/Annual Review of Astronomy and Astrophysics 2017; M.S. Peeples/Nature 2015

    Waiting for Hubble

    That 2009 Hubble telescope upgrade, which made the CGM census possible, almost didn’t happen.

    In a cosmic coincidence, the Hubble telescope’s chief champions were also the first astronomers to figure out how to observe a galaxy’s CGM. Lyman Spitzer of Princeton University and John Bahcall of the Institute for Advanced Study in Princeton, N.J., and other astronomers noticed something strange after the 1963 discovery of quasars [http://cosmology.carnegiescience.edu/timeline/1963] (SN Online: 3/21/14), bright beacons now known to be white-hot disks surrounding supermassive black holes in the centers of distant galaxies.

    Everywhere astronomers looked, quasars’ spectra — the rainbow created when their light is spread out over all wavelengths — were notched with dark holes. Some wavelengths of light weren’t getting through.

    In 1969, Spitzer and Bahcall realized what was going on: The missing light was absorbed by gas at the edges of galaxies, the same stuff that would later be called the CGM. Astronomers had been peering at quasars shining through CGMs like headlights through a fog.

    Not much more could be done at the time, though. Earth’s atmosphere also absorbs light in those same wavelengths, making it difficult to tell which light-blocking atoms were in a galaxy’s CGM and which came from closer to home. Knowing that a CGM was there was one thing; taking its measurements would require something extra.

    Spitzer and Bahcall knew what they needed: a space telescope that could observe from outside Earth’s atmosphere. The pair were two of the most vocal and consistent champions of the Hubble Space Telescope, which launched in 1990. Spitzer’s colleagues called him Hubble’s “intellectual and political father.”

    Bahcall never stopped advocating for Hubble. In February 2005, six months before his death at age 70 from a rare blood disorder, he co-wrote an article in the Los Angeles Times [http://articles.latimes.com/2005/feb/23/opinion/oe-tayloretal23] urging Congress to restore funding for a mission to fix some aging Hubble instruments, which NASA had canceled after the 2003 Columbia space shuttle disaster.

    “What is at stake is not only a piece of stellar technology but our commitment to the most fundamental human quest: understanding the cosmos,” Bahcall and colleagues wrote. “Hubble’s most important discoveries could be in the future.”

    His plea was answered: The space shuttle Atlantis brought astronauts to repair Hubble for the last time in May 2009 (SN Online: 5/19/09). During the repair, the astronauts installed the Cosmic Origins Spectrograph, which could pick up diffuse CGM gas with 30 times the sensitivity of any previous instrument.

    NASA Hubble Cosmic Origins Spectrograph

    Although earlier spectrographs on Hubble had picked out CGMs a few quasar-beams at a time, the new device let astronomers search around dozens of galaxies, using the light of even dimmer quasars.

    “It blew the field wide open,” Werk says.

    Gas flows out from Messier 82, the Cigar galaxy, to its invisible circumgalactic medium in this Hubble image. NASA, ESA, Hubble Heritage Team

    The circumgalactic census

    A team led by Jason Tumlinson of Baltimore’s Space Telescope Science Institute, Hubble’s academic home, made a catalog of 44 galaxies with a quasar sitting behind them from Hubble’s perspective. In a 2011 paper in Science, the researchers reported that every time they looked within 490,000 light-years of a galaxy, they saw spectra dappled with blank spots from atoms absorbing light. That meant that CGMs weren’t odd cloaks worn by just a few galaxies. They were everywhere.

    Tumlinson’s team spent the first few years after Hubble’s upgrade like 19th century naturalists describing new species. The group measured the mass and the chemical makeup of the galaxies’ CGMs and found they were huge cisterns of heavy elements. CGMs contain 10 million times the mass of the sun in oxygen alone. In many cases, the mass of a CGM is comparable to the mass of the entire visible part of its galaxy.

    The finding offers an answer to a long-standing cosmic mystery: How do galaxies have enough star-forming fuel to keep going for billions of years? Galaxies build stars from collapsing clouds of cool gas at a constant rate; the Milky Way, for example, makes one to two solar masses’ worth of stars every year. But there isn’t enough cool gas within the visible part of a galaxy, the disk containing its stars, to support observed rates of star formation.

    “We think that gas probably comes from the CGM,” Werk says. “But exactly how that gas is getting into galaxies, where it gets in, the timescale on which it gets in, are there things that prevent it from getting in? Those are big questions that keep us all awake at night.”

    Werk and Peeples realized that all that mass could help solve two other cosmic bookkeeping problems. All elements heavier than helium (which astronomers lump together as “metals”) are forged by nuclear fusion in the hearts of stars. When stars use up their fuel and explode as supernovas, they scatter those metals around to be folded into the next generation of stars.

    But if you add up all the metals in the stars, gas and dust in a given galaxy’s disk, it’s not enough to account for all the metals the galaxy has ever made. The mismatch gets even worse if you include the hydrogen, helium, electrons and protons — basically all the ordinary matter that should have collected in the galaxy since the Big Bang. Astronomers call all those bits baryons. Galaxies seem to be missing 70 to 95 percent of that stuff.

    So Peeples and Werk led a comprehensive effort to tally all the ordinary matter in about 40 galaxies observed with Hubble’s new spectrometer. The researchers published the results in two 2014 papers in The Astrophysical Journal.

    At the time, Werk reported that at least half of galaxies’ missing ordinary matter can be accounted for in their CGMs. In a 2017 update, Werk and colleagues found that the mass of baryons just in the form of cool gas in a galaxy’s CGM could be nearly 90 billion solar masses [The Astrophysical Journal]. “Obviously, this mass could resolve the galactic missing baryons problem,” the team wrote.

    “It’s a classic science story,” Schawinski says. The researchers had a hypothesis about where the missing material should be and made predictions. The group made observations to test those predictions and found what it sought.

    In a separate study, Peeples showed that although metals are born in galaxies’ starry disks, those metals don’t stay there. Only 20 to 25 percent of the metals a galaxy has ever produced remains in the stars, gas and dust in the disk, where the metals can be incorporated into new stars and planets. The rest probably ends up in the CGM.

    “If you look at all the metals the galaxies ever produced in their whole lifetime, more of them are outside the galaxy than are still inside the galaxy,” Tumlinson says, “which was a huge shock.”

    Recycling centers

    So how did the metals get into the CGM? Quasars’ spectra couldn’t help with that question. Their light shows only a slice through a single galaxy at a single moment in time. But astronomers can track galaxies’ growth and development with computer simulations based on physical rules for how stars and gas behave.

    This strategy revealed the churning, ever-changing nature of gas in galaxies’ CGMs. Simulations such as EAGLE, or Evolution and Assembly of GaLaxies and their Environments, which is run out of Leiden University in the Netherlands, showed that metals can reach CGMs through stars’ violent lives: in powerful winds of radiation blowing away from massive young stars, and in the death throes of supernovas spraying metals far and wide.

    This EAGLE simulation shows that, over time, metals (colors) move away from the center of a galaxy to the circumgalactic medium. J. Tumlinson, M.S. Peeples and J.K. Werk/Annual Review of Astronomy and Astrophysics 2017

    Once the metals are in the CGM, though, they don’t always stay put. In simulations, galaxies seem to use the same gas over and over again.

    “It’s basically just gravity,” Peeples says. “Throw a baseball up, and it’ll come back to the ground.” The same goes for gas flowing out of galaxies: Unless the gas travels fast enough to escape the galaxy’s gravity altogether, those atoms will eventually fall back into the disk — and form new stars.

    Some simulations show discrete gas parcels making the trip from a galaxy’s disk out into the CGM and back again several times. Together, CGMs and their galaxies are giant recycling devices.

    That means that the atoms that make up planets, plants and people may have taken several trips to circumgalactic space before becoming part of us. Over hundreds of millions of years, the atoms that eventually became part of you traveled hundreds of thousands of light-years.

    “This is my favorite thing,” Tumlinson says. “At some point, your carbon, your oxygen, your nitrogen, your iron was out in intergalactic space.”

    How galaxies die

    But not all galaxies get their CGM gas back. Losing the gas could shut off star formation in a galaxy for good. No one knows how star formation shuts off, or quenches. But the answer is probably in the CGM.

    Galaxies come in two main forms: young spiral galaxies that are making stars and old blobby galaxies where star formation is quenched (SN Online: 4/23/18).

    “How galaxies quench and why they stay that way is one of the most important questions in galaxy formation generally,” Tumlinson says. “It just has to have something to do with the gas supply.”

    Reading what’s not there

    Using light from a quasar (QSO), researchers can “see” CGMs. In this example, spectra from two galaxies, G1 and G2, have certain wavelengths missing (red, in bottom boxes) where the CGM atoms are absorbing light.


    One possibility, suggested in a paper posted online February 20 in The Astrophysical Journal, is that sprays of supernova-heated gas could get stripped from galaxies. Physicist Chad Bustard of the University of Wisconsin–Madison and colleagues simulated the Large Magellanic Cloud, a satellite galaxy of the Milky Way, and found that the small galaxy’s outflowing gas was swept away by the slight pressure of the galaxy’s movement around the Milky Way.

    Alternatively, a dead galaxy’s CGM gas could be too hot to sink into the galaxy and form stars. If so, star-forming galaxies should have CGMs full of cold gas, and dead galaxies should be shrouded in hot gas. Hot gas would stay floating above the galactic disk like a hot air balloon, too buoyant to sink in and form stars.

    But Hubble saw the opposite. Star-forming galaxies had CGMs chock-full of oxygen-VI — meaning that the gas was so hot (a million degrees Celsius or more) that oxygen atoms lost five of their original electrons. Dead galaxies had surprisingly little oxygen-VI.

    “That was puzzling,” Tumlinson says. “If theory told us anything, it should have gone the other way.”

    In 2016, Benjamin Oppenheimer, a computational astrophysicist at the University of Colorado Boulder, suggested a solution: The “dead” galaxies didn’t lack oxygen at all. The gas was just too hot for Hubble to observe. “In fact, there is even more oxygen around those passive galaxies,” Oppenheimer says.

    All that hot gas could potentially explain why those galaxies died — except that these galaxies were full of star-forming cold gas, too.

    “The dead galaxies have plenty of fuel left in the tank,” Tumlinson says. “We don’t know why they’re not using it. Everybody’s chasing that problem.”

    Grabbing at the elephant

    The chase comes at a good time. Until recently, observers had no way to map a single galaxy’s CGM. Researchers have had to add up dozens of quasar beams to understand the composition of CGMs on average.

    “We’ve been like the three blind people grabbing at the elephant,” says John O’Meara, an observational astronomer at Saint Michael’s College in Colchester, Vt.

    Teams using two new spectrographs — KCWI, the Keck Cosmic Web Imager on the Keck telescope in Hawaii, and MUSE, the Multi Unit Spectroscopic Explorer on the Very Large Telescope in Chile — are racing to change that.

    Keck Cosmic Web Imager schematic

    Keck Cosmic Web Imager

    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level,

    ESO MUSE on the VLT on Yepun (UT4),

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo

    These instruments, called integral field spectrographs, can read spectra across a full galaxy all at once. Given enough background light, astronomers can now examine a single galaxy’s entire CGM. Finally, astronomers have a way to test theories of how gas circulates into and out of a galaxy.

    A Chilean team, led by astronomer Sebastian Lopez of the University of Chile in Santiago and colleagues, used MUSE to observe a small dim galaxy that happens to be sandwiched between a bright, distant galaxy and a massive galaxy cluster closer to Earth. The cluster acts as a gravitational lens, distorting the image of the distant galaxy into a long bright arc (SN: 3/10/12, p. 4). The light from that arc filtered through the CGM of the sandwiched galaxy, which the team called G1, at 56 different points.

    Surprisingly, G1’s CGM was lumpy, not smooth as expected, the team reported in the Feb. 22 Nature. “The assumption has been that that gas is distributed homogeneously around every system,” Lopez says. “This is not the case.”

    MUSE makes a mark

    Light from a source galaxy is deflected and magnified by an intervening galaxy cluster to form the bright arc seen in the projected image at far right. Unlike a quasar’s narrow beam of light, the extensive arc lights up a large area of galaxy G1’s CGM, showing it is surprisingly lumpy.


    O’Meara is leading a group that is hot on Lopez’s trail. Last year, while KCWI was being installed, O’Meara got an hour of observing time and was able to see hydrogen — which is associated with cool, star-forming gas — in the CGM of another galaxy backlit by a bright lensed arc. He’s not ready to discuss the results in detail yet, but the team is submitting a paper to Science.

    Meanwhile, Peeples’ team is revisiting how computers render CGMs. “The resolution of the circumgalactic medium in simulations is, um, bad,” she says. Existing simulations are good at matching the visible properties of galaxies — their stars, the gas between the stars, and the overall shapes and sizes. But they “utterly fail at reproducing the properties of the circumgalactic medium,” she says.

    So she’s running a new set of simulations called FOGGIE, which focus on CGMs for the first time. “We’re finding that it changes everything,” she says: The shape, star formation history and even the orientation of the galaxy in space look different.

    Together, the new observations and simulations suggest that the CGM’s function in the life cycle of a galaxy has been underestimated. Theorists like Peeples and observers like O’Meara are working together to make new predictions about how the CGM should look. Then the researchers will check real galaxies to see if they match.

    “Molly will post a really amazing new render of a simulation on Slack, and I’ll go, ‘Holy crap, that looks weird!’ ” O’Meara says. “I’ll go scampering off to find a similar example in the data, and we get into this positive feedback loop of going ‘Holy crap! Holy crap!’ ”

    While future circumgalactic studies will focus on gathering spectra from full CGMs, Tumlinson is hoping to squeeze more information out of Hubble while he still can. Hubble made CGM studies possible, but the telescope is 28 years old, and probably has less than a decade left. Hubble’s spectrograph is still the best at observing certain atoms in CGMs to help reveal the gaseous halos’ secrets. “It’s something we definitely want to do,” he says, “before Hubble ends up in the ocean.”

    See the full article here .


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  • richardmitnick 7:50 am on July 25, 2018 Permalink | Reply
    Tags: , , , , Galaxy BX418, Keck Cosmic Web Imager,   


    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft) above sea level, with Subaru and IRTF (NASA Infrared Telescope Facility). Vadim Kurland

    From Keck Observatory


    A team of astronomers has discovered a new way to unlock the mysteries of how the first galaxies formed and evolved.

    In a study published today in The Astrophysical Journal Letters, lead author Dawn Erb of the University of Wisconsin-Milwaukee and her team – for the very first time – used new capabilities at W. M. Keck Observatory on Maunakea, Hawaii to examine Q2343-BX418, a small, young galaxy located about 10 billion light years away from Earth.

    This distant galaxy is an analog for younger galaxies that are too faint to study in detail, making it an ideal candidate for learning more about what galaxies looked like shortly after the birth of the universe.

    BX418 is also attracting astronomers’ attention because its gas halo is giving off a special type of light.

    “In the last several years, we’ve learned that the gaseous halos surrounding galaxies glow with a particular ultraviolet wavelength called Lyman alpha emission. There are a lot of different theories about what produces this Lyman alpha emission in the halos of galaxies, but at least some of it is probably due to light that is originally produced by star formation in the galaxy being absorbed and re-emitted by gas in the halo,” said Erb.

    An artist’s concept showing the gaseous halo surrounding a galaxy, illuminated by a narrow band of ultraviolet light called Lyman alpha emission. BX418’s gas halo is about ten times the size of the galaxy itself. CREDIT: T. KLEIN, UWM

    Erb’s team, which includes Charles Steidel and Yuguang Chen of Caltech, used one of the observatory’s newest instruments, the Keck Cosmic Web Imager (KCWI), to perform a detailed spectral analysis of BX418’s gas halo; its properties could offer clues about the stars forming within the galaxy.

    Keck Cosmic Web Imager schematic

    Keck Cosmic Web Imager

    “Most of the ordinary matter in the universe isn’t in the form of a star or a planet, but gas. And most of that gas exists not in galaxies, but around and between them,” said Erb.

    The halo is where gas enters and exits the system. The gas surrounding galaxies can fuel them; gas from within a galaxy can also escape into the halo. This inflow and outflow of gas influences the fate of stars.

    “The inflow of new gas accreting into a galaxy provides fuel for new star formation, while outflows of gas limit a galaxy’s ability to form stars by removing gas,” says Erb. “So, understanding the complex interactions happening in this gaseous halo is key to finding out how galaxies form stars and evolve.”

    This study is part of a large ongoing survey that Steidel has been leading for many years. Previously, Steidel’s team studied BX418 using other instruments at Keck Observatory.

    This most recent study using KCWI adds detail and clarity to the image of the galaxy and its gas halo that was not possible before; the instrument is specifically engineered to study wispy currents of faint gas that connect galaxies, known as the cosmic web.

    “Our study was really enabled by the design and sensitivity of this new instrument. It’s not just an ordinary spectrograph—it’s an integral field spectrograph, which means that it’s a sort of combination camera and spectrograph, where you get a spectrum of every pixel in the image,” said Erb.

    The power of KCWI, combined with the Keck telescopes’ location on Maunakea where viewing conditions are among the most pristine on Earth, provides some of the most detailed glimpses of the cosmos.

    Erb’s team used KCWI to take spectra of the Lyman alpha emission of BX418’s halo. This allowed them to trace the gas, plot its velocity and spatial extent, then create a 3-D map showing the structure of the gas and its behavior.

    The team’s data suggests that the galaxy is surrounded by a roughly spherical outflow of gas and that there are significant variations in the density and velocity range of this gas.

    Astronomer Dawn Erb, PhD, University of Wisconsin-Milwaukee, has devoted her life to uncovering the secrets of galaxy growth and evolution. CREDIT: T. FOX, UWM

    Erb says this analysis is the first of its kind. Because it has only been tested on one galaxy, other galaxies need to be studied to see if these results are typical.

    Now that the team has discovered a new way to learn about the properties of the gaseous halo, the hope is that further analysis of the data they collected and computer simulations modeling the processes will yield additional insights into the characteristics of the first galaxies in our universe.

    “As we work to complete more detailed modeling, we will be able to test how the properties of Lyman alpha emission in the gas halo are related to the properties of the galaxies themselves, which will then tell us something about how the star formation in the galaxy influences the gas in the halo,” Erb said.

    Erb is supported by the US National Science Foundation through the Faculty Early Career Development Program, grant AST-125591. Steidel and Chen acknowledge support from the Caltech/JPL President’s and Director’s Fund.


    The Keck Cosmic Web Imager (KCWI) is designed to provide visible band, integral field spectroscopy with moderate to high spectral resolution formats and excellent sky-subtraction. The astronomical seeing and large aperture of the telescope will enable studies of the connection between galaxies and the gas in their dark matter halos, stellar relics, star clusters, and lensed galaxies. Support for this project was provided by The Heising-Simons Foundation, Gordon and Betty Moore Foundation, Mt. Cuba Astronomical Foundation, and other Friends of Keck Observatory.

    See the full article here .

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    To advance the frontiers of astronomy and share our discoveries with the world.

    The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes on the summit of Mauna Kea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometer and world-leading laser guide star adaptive optics systems. Keck Observatory is a private 501(c) 3 non-profit organization and a scientific partnership of the California Institute of Technology, the University of California and NASA.

    Today Keck Observatory is supported by both public funding sources and private philanthropy. As a 501(c)3, the organization is managed by the California Association for Research in Astronomy (CARA), whose Board of Directors includes representatives from the California Institute of Technology and the University of California, with liaisons to the board from NASA and the Keck Foundation.

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  • richardmitnick 12:34 pm on April 14, 2017 Permalink | Reply
    Tags: , , , , , Keck Cosmic Web Imager,   

    From Caltech: “Keck Cosmic Web Imager Achieves ‘First Light'” 

    Caltech Logo



    Whitney Clavin
    (626) 395-1856

    Keck Observatory

    A Caltech-built instrument designed to study the mysteries of the cosmic web—streams of gas connecting galaxies—has captured its first image, an event astronomers call “first light.” The instrument, called the Keck Cosmic Web Imager, or KCWI, was recently installed on the W. M. Keck Observatory in Hawaii.

    Hector Rodriguez, senior mechanical technician, works on the Keck Cosmic Web Imager in a clean room at Caltech. Credit: Caltech

    KCWI captures highly detailed spectral images of cosmic objects to reveal their temperature, motion, density, mass, distance, chemical composition, and more. The instrument is designed to study the wispy cosmic web; it will also observe many other astronomical phenomena, including young stars, evolved stars, supernovas, star clusters, and galaxies.

    “I’m incredibly excited. These moments happen only a few times in one’s life as a scientist,” says principal investigator Christopher Martin, professor of physics at Caltech. “To take a powerful new instrument, a tool for looking at the universe in a completely novel way, and install it at the greatest observatory in the world is a dream for an astronomer. This is one of the best days of my life.”

    Martin and his Caltech team, in collaboration with scientists at UC Santa Cruz and with industrial partners, designed and built the 5-ton instrument—about the size of an ice cream truck. It was then shipped from California to Hawaii on January 12. Since then, Keck Observatory’s team has been working diligently to install and test KCWI on Keck II, one of the twin 10-meter Keck Observatory telescopes.

    “KCWI will really raise the bar in terms of Keck Observatory’s capabilities,” says Anne Kinney, chief scientist at Keck Observatory. “I think it will become the most popular instrument we have, because it will be able to do a great breadth of science, increasing our ability to understand and untangle the effects of dark matter in galaxy formation.”

    The W. M. Keck Observatory is a private 501(c)3 nonprofit organization and a scientific partnership of Caltech, the University of California, and NASA.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”
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  • richardmitnick 3:07 pm on January 14, 2017 Permalink | Reply
    Tags: , , , , , , Keck Cosmic Web Imager   

    From Caltech via EurekaAlert: “New Caltech instrument poised to image the cosmic web” 

    Caltech Logo



    Whitney Clavin

    Keck Cosmic Web Imager ships from Caltech to Keck Observatory

    Hector Rodriguez, senior mechanical technician, works on the Keck Cosmic Web Imager in a clean room at Caltech. Caltech

    An instrument designed to image the vast web of gas that connects galaxies in the universe has been shipped from Los Angeles to Hawaii, where it will be integrated into the W. M. Keck Observatory.

    Keck Observatory, Mauna Kea, Hawaii, USA
    Keck Observatory, Mauna Kea, Hawaii, USA

    The instrument, called the Keck Cosmic Web Imager, or KCWI, was designed and built by a team at Caltech led by Professor of Physics Christopher Martin. It will be one of the best instruments in the world for taking spectral images of cosmic objects–detailed images where each pixel can be viewed in all wavelengths of visible light. Such high-resolution spectral information will enable astronomers to study the compositions, velocities, and masses of many objects, such as stars and galaxies, in ways that were not possible before.

    One of KCWI’s main goals, and a passion of Martin’s for the past 30 years, is to answer the question: What is the gas around galaxies doing?

    “For decades, astronomers have demonstrated that galaxies evolve. Now we’re trying to figure out how and why,” says Martin. “We know the gas around galaxies is ultimately fueling them, but it is so faint–we still haven’t been able to get a close look at it and understand how this process works.”

    Martin and his team study what is called the cosmic web–a vast network of streams of gas between galaxies. Recently, the scientists have found evidence supporting what is called the cold flow model, in which this gas funnels into the cores of galaxies, where it condenses and forms new stars.

    The forming galaxy with binary quasars as it fits into the timeline of the Universe. We’re seeing it 10 billion years ago, during the epoch of galaxy formation. Credit: Caltech Academic Media Technologies

    Researchers had predicted that the gas filaments would first flow into a large ring-like structure around the galaxy before spiraling into it–exactly what Martin and his team found using the Palomar Cosmic Web Imager, a precursor to KCWI, at Caltech’s Palomar Observatory near San Diego.

    Caltech Palomar Cosmic Web Imager
    Caltech Palomar Cosmic Web Imager

    “We measured the kinematics, or motion, of the gas around a galaxy and found a very large rotating disk connected to a gas filament,” says Martin. “It was the smoking gun for the cold flow model.”

    With KCWI, the researchers will get a closer look at the gas filaments and ring-like structures around galaxies that range from 10 to 12 billion light-years away, an era when our universe was roughly 2 to 4 billion years old. Not only can KCWI take more detailed pictures than the Palomar Cosmic Web Imager, it has other advances such as better mirror coatings. The combination of these improvements with the fact that KCWI is being installed at one of the twin 10-meter Keck telescopes–the world’s largest observatory with some of the darkest known skies on Earth–means that KCWI will have an improved performance by more than an order of magnitude over the Palomar Cosmic Web Imager.

    KCWI will map the gas flowing from the intergalactic medium–the space between galaxies–into many young galaxies, revealing, for the first time, the dominant mode of galaxy formation in the early universe. The instrument will also search for supergalactic winds from galaxies that drive gas back into the intergalactic medium. How gas flows into and out of forming galaxies is the central open question in the formation of cosmic structures.

    “We designed KCWI to study very dim and diffuse objects, our main emphasis being on the wispy cosmic web and the interactions of galaxies with their surroundings,” says Mateusz (Matt) Matuszewski, the instrument scientist for the project.

    KCWI is also designed to be more a general-purpose instrument than the Palomar’s Cosmic Web Imager, which is mainly for studies of the cosmic web. It will study everything from gas jets around young stars to the winds of dead stars and supermassive black holes and more. “The instrument is really versatile,” says Matuszewski. “Observers can configure the optics to adjust the spatial and spectral scales and resolutions to suit their interests.”

    The nuts and bolts of KCWI

    Scientists and engineers have been busy assembling the highly complex elements of the KCWI instrument at Caltech since 2012. The instrument is about the size of an ice cream truck and weighs over 4,000 kilograms. The core feature of KCWI is its ability to capture spectral information about objects, such as galaxies, across a wide image. Typically, astronomers capture spectra using instruments called spectrographs, which have narrow slit-shaped windows. The spectrograph breaks apart light from the slit into each of the colors making up the target object, just like a prism that spreads light into a rainbow. But traditional spectrographs cannot be used to capture spectral information across an entire image.

    “Traditional spectrographs use multiple small slits to capture many stars or the cores of many galaxies,” says Martin. “Now, we want to look at features that are extended across the sky, such as stellar jets and galaxies, which have complex structures, velocities, and gas flows. If you can only look through a slit, you can only see a small part of what is going on. But we want to see the whole picture. That’s why we need an imaging spectrograph, a device that gives you an image for every single wavelength across a wide view.”

    To create a spectrograph that can image more extended objects like galaxies, KCWI uses what is called an integral field design, which basically divides an image up into 24 slits, and gathers all the spectral information at once.

    “If you’re looking at something big in the sky, it’s inefficient to just have one slit and step your way across that object, so an integral field spectrograph combines a number of slit-shaped mirrors together across a continuous field of view,” says Patrick Morrissey, the project scientist for KCWI who now works at JPL. “Imagine looking into a broken mirror–the reflected image is shifted around depending on the angles of the pieces. This is how the integral field spectrograph works. A series of mirrors works together to make a square-shaped stack of slits across an image appear as a single traditional vertical slit.”

    KCWI has the highest spectral resolution of any integral field spectrograph, which means it can better break apart the rainbow of light to see more colors, or wavelengths. The first phase of the instrument, now on its way to Keck, covers the blue side of the visible spectrum, spanning wavelength ranges from 3500 to 5600 Angstroms. A second phase, extending coverage to the red side of the spectrum, out to 10400 Angstroms, will be built next.

    KCWI to Climb Mauna Kea

    After KCWI arrives in Hawaii on January 18, engineers will guide it up to the top of Mauna Kea, where Keck is perched. A series of checkout and alignment tests is planned, and will be followed in a few months by the first observations through the Keck telescope.

    “There are train tracks around the telescope where the instruments are installed,” says Morrissey. “It’s like one of those old railroad roundhouses where the train would come in and they would spin it to an available space for storage. The telescope turns around, points to the instrument that the astronomer wants to use, and then they roll that instrument on. Soon KCWI will becomes part of the telescope.”

    KCWI is funded by the National Science Foundation, through the Association of Universities for Research in Astronomy (AURA) program, and by the Heising-Simons Foundation, the W.M. Keck Foundation, the Caltech Division of Physics, Mathematics and Astronomy, and the Caltech Optical Observatories.

    See the full article here .

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    The California Institute of Technology (commonly referred to as Caltech) is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering. Its 124-acre (50 ha) primary campus is located approximately 11 mi (18 km) northeast of downtown Los Angeles. “The mission of the California Institute of Technology is to expand human knowledge and benefit society through research integrated with education. We investigate the most challenging, fundamental problems in science and technology in a singularly collegial, interdisciplinary atmosphere, while educating outstanding students to become creative members of society.”

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