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  • richardmitnick 12:49 pm on April 3, 2019 Permalink | Reply
    Tags: , , , Collaborating Institutions - Member Institutions and representatives, , DESI-Dark Energy Spectroscopic Instrument,   

    From Lawrence Berkeley National Lab: “Dark Energy Instrument’s Lenses See the Night Sky for the First Time” 

    Berkeley Logo

    From Lawrence Berkeley National Lab

    April 3, 2019
    Glenn Roberts Jr.

    LBNL/DESI spectroscopic instrument on the Mayall 4-meter telescope at Kitt Peak National Observatory starting in 2018

    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA, Altitude 2,120 m (6,960 ft)

    Kitt Peak National Observatory of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers 55 mi west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft)

    1
    DESI “first light” image of the Whirlpool Galaxy, also known as Messier 51. This image was obtained the first night of observing with the DESI Commissioning Instrument on the Mayall Telescope at the Kitt Peak National Observatory in Tucson, Arizona; an r-band filter was used to capture the red light from the galaxy. (Credit: DESI Collaboration)

    On April 1, the dome of the Mayall Telescope near Tucson, Arizona, opened to the night sky, and starlight poured through the assembly of six large lenses that were carefully packaged and aligned for a new instrument that will launch later this year.

    Just hours later, scientists produced the first focused images with these precision lenses – the largest is 1.1 meters in diameter – during this early test spin, marking an important “first light” milestone for the Dark Energy Spectroscopic Instrument, or DESI. This first batch of images homed in on the Whirlpool Galaxy to demonstrate the quality of the new lenses.

    ”It was an incredible moment to see those first images on the control room monitors,” said Connie Rockosi, who is leading this early commissioning of the DESI lenses. “A whole lot of people have worked really hard on this, and it’s really exciting to show how much has come together already.”

    This phase of the project will continue for about six weeks and will require the efforts of several onsite scientists and remote observers, noted Rockosi, a professor of astronomy and astrophysics at UC Santa Cruz.

    When completed later this year, DESI will see and measure the sky’s light in a far different way than this assembly of lenses. It is designed to take in thousands of points of light instead of a single, large picture.

    The finished DESI will measure the light of tens of millions of galaxies reaching back 12 billion light-years across the universe. It is expected to provide the most precise measurement of the expansion of the universe and provide new insight into dark energy, which scientists explain is causing this expansion to accelerate.


    In this video, DESI project participants share their insight and excitement about the project and its potential for new and unexpected discoveries. (Credit: Marilyn Chung/Berkeley Lab, DESI Collaboration)

    DESI’s array of 5,000 independently swiveling robotic positioners (see a related video: 5,000 Robots Merge to Map the Universe in 3D), each carrying a thin fiber-optic cable, will automatically move into preset positions with accuracy to within several microns (millionths of a meter). Each positioner is programmed to point its fiber-optic cable at an object to gather its light.

    That light will be channeled through the cables to a series of 10 devices known as spectrographs that will separate the light into thousands of colors. The light measurements, known as spectra, will provide detailed information about objects’ distance and the rate at which they are moving away from us, providing fresh insight about dark energy.

    DESI’s lenses are housed in a barrel-shaped device known as a corrector that is attached above the telescope’s primary mirror, and the corrector is moved and focused by a surrounding device known as a hexapod.

    Fermi National Accelerator Laboratory (Fermilab) researchers led the design, construction, and initial testing of the corrector barrel, hexapod and supporting structures that hold the lenses in alignment.

    “Our entire team is pleased to see this instrument achieve first light,” said Gaston Gutierrez, the Fermilab scientist who managed this part of the project. “It was a great challenge building such large devices to within the precision of a hair. We’re happy to see these systems come together.”

    2
    A view of the lenses in DESI’s corrector. The largest lens measures over a meter across.

    The giant corrector barrel and hexapod, which together weigh about 5 tons, must maintain alignment with the telescope’s large reflector mirror that is 12 meters below, all while compensating for the movement of the telescope’s assemblage of massive components as it swings across the sky.

    “This is a big step up. It’s a leap into the future for the Mayall Telescope that will enable exciting new scientific discoveries,” said Michael Levi, DESI’s director and a physicist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), which is the lead institution in the international DESI collaboration. “The team has been working on the new corrector for the past five years, so it was quite an experience seeing $10 million of optics lifted by the crane during installation.”

    4
    DESI’s cylindrical commissioning instrument, top left, sits just above the corrector barrel (middle) on the Mayall Telescope. The commissioning instrument is designed to test the performance of DESI’s lenses, which are stacked inside the corrector barrel, using a set of five precisely positioned digital cameras. (Credit: Bill McCollam and Paul Demmer/KPNO, NOAO/AURA/NSF)

    The new set of lenses (see a related video: The Life of a Lens) expands the telescope’s viewing window by about 16 times, enabling DESI to map about one-third of the visible sky several times during its five-year mission.

    Peter Doel, a professor at University College London, led the team that designed the new optical system. “We had a half-dozen vendors involved with making and polishing the glass. One mistake would have spoiled everything. It’s thrilling to know that they survived the journey and work so well.”

    “This was kind of the moment of truth,” said David Schlegel, a DESI project scientist. “We have been biting our nails.”

    David Sprayberry, the National Optical Astronomy Observatory (NOAO) site director at Kitt Peak, said, “We have an amazing, multitalented team to make sure that everything is working properly,” including engineers, astronomers, and telescope operators working in shifts. NOAO operates the Mayall Telescope and its Kitt Peak National Observatory site.

    He noted the challenge in updating the sturdy, decades-old telescope, which started up in 1973, with high-precision equipment. “Ultimately we must make sure DESI can target to within 5-micron accuracy – not much larger than a human hair,” he said. That’s a big thing for something so heavy and big.” The entire moving weight of the Mayall Telescope is 375 tons.

    Rockosi said there was intensive pre-planning for the corrector’s early testing, and many of the tasks during this testing stage are focused on gathering data from evening observations. While DESI scientists have created automated controls to help position, focus, and align all of the equipment, this testing run allows the team to fine-tune these automated tools.

    “We’ll look at bright stars and test how well we can keep the telescope targeted in the same place, and measure image quality,” Rockosi said. “We will test that we can repeatedly and reliably keep those lenses in the best possible alignment.”

    5
    Paul Martini, an astronomy professor at Ohio State University, inspects DESI’s commissioning instrument before it is installed on the 4-meter Mayall Telescope at Kitt Peak National Observatory. (Credit: NOAO/AURA/NSF)

    The precision testing of the corrector is made possible by an instrument – now mounted atop the telescope – that was designed and built by Ohio State University researchers. This 1-ton device, which features five digital cameras and measuring tools supplied by Yale University, and electronics supplied by the University of Michigan, is known as the commissioning instrument.

    6
    Workers raise DESI’s commissioning instrument into position for installation. The instrument is designed to test the performance of DESI’s lenses. (Credit: NOAO/AURA/NSF)

    This temporary instrument was built at the same weight and installed at the same spot where DESI’s focal plane will be installed once it is fully assembled. The focal plane will carry DESI’s robotic positioners. The commissioning instrument simulates how the telescope will perform when carrying the full complement of DESI components, and is verifying the quality of DESI’s lenses.

    “One of the biggest challenges with the commissioning instrument was aligning all five cameras with the corrector’s curved focal surface,” said Paul Martini, an astronomy professor at Ohio State University who led the R&D and installation of the commissioning instrument and is now overseeing its use. “Another was measuring their positions to a few millionths of a meter, which is far more precise than most astronomical instruments.” This positioning will ensure truer measurements of the lenses’ performance.

    He said he is looking forward to the installation of DESI’s focal plane later this year. That will pave the way for DESI’s official “first light” of its robotic positioners and the start of its galaxy measurements.

    “What got me excited about this field in the first place was going to telescopes and taking data, so it will be fun to have this next step,” he said.

    DESI is supported by the U.S. Department of Energy’s Office of Science; the U.S. National Science Foundation, Division of Astronomical Sciences under contract to the National Optical Astronomy Observatory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the National Council of Science and Technology of Mexico; the Ministry of Economy of Spain; and DESI member institutions. The DESI scientists are honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation. View the full list of DESI collaborating institutions, and learn more about DESI here: http://www.desi.lbl.gov.

    Collaborating Institutions
    Member Institutions and representatives:

    Argonne National Laboratory – Salman Habib
    Barcelona – Madrid RPG – Francisco Castander
    Boston University – Steve Ahlen
    Brookhaven National Laboratory – Anze Slosar
    Carnegie Mellon University – Shirley Ho
    Cornell University – Rachel Bean
    École Polytechnique Fédérale de Lausanne (EPFL)– Jean-Paul Kneib
    Eidgenössische Technische Hochschule Zürich (ETHZ) – Alexandre Refregier
    Fermi National Accelerator Laboratory – Elizabeth Buckley-Geer
    GMT RPG – Francisco Prada
    Harvard University – Daniel Eisenstein
    Korea Astronomy and Space Science Institute (KASI) – Yong-Seon Song
    Korea Institute for Advanced Study (KIAS) – Changbom Park
    Laboratoire de Physique Nucléaire et de Hautes Énergies (LPNHE) – Julien Guy
    Lawrence Berkeley National Laboratory – David Schlegel
    LinEA-Brazil – Luiz da Costa
    Max Planck Institut fur Extraterrestriche Physik – Ariel Sanchez
    Mexico RPG – Axel de la Macorra
    National Astronomical Observatories of the Chinese Academy of Sciences (NAOC) – Shude Mao
    National Optical Astronomy Observatory – Robert Blum
    Ohio State University – Klaus Honscheid
    Ohio University – Hee-Jong Seo
    Shanghai Jiao Tong University – Ying Zu
    Siena College – John Moustakas
    SLAC National Accelerator Laboratory – Aaron Roodman
    Southern Methodist University – Bob Kehoe
    Swinburne University of Technology – Chris Blake
    UK RPG – John Peacock
    Universidad de los Andes – Jamie Forero
    Universitat de Barcelona – Licia Verde
    Université Aix-Marseille (AMU) – Jean-Gabriel Cuby
    University College London – Ofer Lahav
    University of Arizona – Xiaohui Fan
    University of California, Berkeley – Jerry Edelstein
    University of California, Irvine – David Kirkby
    University of California, Santa Cruz – Connie Rockosi
    University of Durham – Carlos Frenk
    University of Michigan – Gregory Tarle
    University of Paris Saclay – Christophe Yeche
    University of Pennsylvania – Adam Lidz
    University of Pittsburgh – Jeffrey Newman
    University of Portsmouth – Will Percival
    University of Queensland – Tamara Davis
    University of Rochester – Regina Demina
    University of Toronto – Ray Carlberg
    University of Utah – Kyle Dawson
    University of Wyoming – Adam Myers
    Yale University – Charles Baltay

    See the full article here .

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    In the world of science, Lawrence Berkeley National Laboratory (Berkeley Lab) is synonymous with “excellence.” Thirteen Nobel prizes are associated with Berkeley Lab. Seventy Lab scientists are members of the National Academy of Sciences (NAS), one of the highest honors for a scientist in the United States. Thirteen of our scientists have won the National Medal of Science, our nation’s highest award for lifetime achievement in fields of scientific research. Eighteen of our engineers have been elected to the National Academy of Engineering, and three of our scientists have been elected into the Institute of Medicine. In addition, Berkeley Lab has trained thousands of university science and engineering students who are advancing technological innovations across the nation and around the world.

    Berkeley Lab is a member of the national laboratory system supported by the U.S. Department of Energy through its Office of Science. It is managed by the University of California (UC) and is charged with conducting unclassified research across a wide range of scientific disciplines. Located on a 202-acre site in the hills above the UC Berkeley campus that offers spectacular views of the San Francisco Bay, Berkeley Lab employs approximately 3,232 scientists, engineers and support staff. The Lab’s total costs for FY 2014 were $785 million. A recent study estimates the Laboratory’s overall economic impact through direct, indirect and induced spending on the nine counties that make up the San Francisco Bay Area to be nearly $700 million annually. The Lab was also responsible for creating 5,600 jobs locally and 12,000 nationally. The overall economic impact on the national economy is estimated at $1.6 billion a year. Technologies developed at Berkeley Lab have generated billions of dollars in revenues, and thousands of jobs. Savings as a result of Berkeley Lab developments in lighting and windows, and other energy-efficient technologies, have also been in the billions of dollars.

    Berkeley Lab was founded in 1931 by Ernest Orlando Lawrence, a UC Berkeley physicist who won the 1939 Nobel Prize in physics for his invention of the cyclotron, a circular particle accelerator that opened the door to high-energy physics. It was Lawrence’s belief that scientific research is best done through teams of individuals with different fields of expertise, working together. His teamwork concept is a Berkeley Lab legacy that continues today.

    A U.S. Department of Energy National Laboratory Operated by the University of California.

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  • richardmitnick 10:52 am on March 25, 2019 Permalink | Reply
    Tags: , , , , DESI-Dark Energy Spectroscopic Instrument, , ExaLearn, , , , ,   

    From insideHPC: “ExaLearn Project to bring Machine Learning to Exascale” 

    From insideHPC

    March 24, 2019

    As supercomputers become ever more capable in their march toward exascale levels of performance, scientists can run increasingly detailed and accurate simulations to study problems ranging from cleaner combustion to the nature of the universe. Enter ExaLearn, a new machine learning project supported by DOE’s Exascale Computing Project (ECP), aims to develop new tools to help scientists overcome this challenge by applying machine learning to very large experimental datasets and simulations.

    1
    The first research area for ExaLearn’s surrogate models will be in cosmology to support projects such a the LSST (Large Synoptic Survey Telescope) now under construction in Chile and shown here in an artist’s rendering. (Todd Mason, Mason Productions Inc. / LSST Corporation)

    “The challenge is that these powerful simulations require lots of computer time. That is, they are “computationally expensive,” consuming 10 to 50 million CPU hours for a single simulation. For example, running a 50-million-hour simulation on all 658,784 compute cores on the Cori supercomputer NERSC would take more than three days.

    NERSC

    NERSC Cray Cori II supercomputer at NERSC at LBNL, named after Gerty Cori, the first American woman to win a Nobel Prize in science

    NERSC Hopper Cray XE6 supercomputer


    LBL NERSC Cray XC30 Edison supercomputer


    The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

    NERSC PDSF


    PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

    Future:

    Cray Shasta Perlmutter SC18 AMD Epyc Nvidia pre-exascale supeercomputer

    Running thousands of these simulations, which are needed to explore wide ranges in parameter space, would be intractable.

    One of the areas ExaLearn is focusing on is surrogate models. Surrogate models, often known as emulators, are built to provide rapid approximations of more expensive simulations. This allows a scientist to generate additional simulations more cheaply – running much faster on many fewer processors. To do this, the team will need to run thousands of computationally expensive simulations over a wide parameter space to train the computer to recognize patterns in the simulation data. This then allows the computer to create a computationally cheap model, easily interpolating between the parameters it was initially trained on to fill in the blanks between the results of the more expensive models.

    “Training can also take a long time, but then we expect these models to generate new simulations in just seconds,” said Peter Nugent, deputy director for science engagement in the Computational Research Division at LBNL.

    From Cosmology to Combustion

    Nugent is leading the effort to develop the so-called surrogate models as part of ExaLearn. The first research area will be cosmology, followed by combustion. But the team expects the tools to benefit a wide range of disciplines.

    “Many DOE simulation efforts could benefit from having realistic surrogate models in place of computationally expensive simulations,” ExaLearn Principal Investigator Frank Alexander of Brookhaven National Lab said at the recent ECP Annual Meeting.

    “These can be used to quickly flesh out parameter space, help with real-time decision making and experimental design, and determine the best areas to perform additional simulations.”

    The surrogate models and related simulations will aid in cosmological analyses to reduce systematic uncertainties in observations by telescopes and satellites. Such observations generate massive datasets that are currently limited by systematic uncertainties. Since we only have a single universe to observe, the only way to address these uncertainties is through simulations, so creating cheap but realistic and unbiased simulations greatly speeds up the analysis of these observational datasets. A typical cosmology experiment now requires sub-percent level control of statistical and systematic uncertainties. This then requires the generation of thousands to hundreds of thousands of computationally expensive simulations to beat down the uncertainties.

    These parameters are critical in light of two upcoming programs:

    The Dark Energy Spectroscopic Instrument, or DESI, is an advanced instrument on a telescope located in Arizona that is expected to begin surveying the universe this year.

    LBNL/DESI Dark Energy Spectroscopic Instrument for the Nicholas U. Mayall 4-meter telescope at Kitt Peak National Observatory near Tucson, Ariz, USA


    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA, Altitude 2,120 m (6,960 ft)

    DESI seeks to map the large-scale structure of the universe over an enormous volume and a wide range of look-back times (based on “redshift,” or the shift in the light of distant objects toward redder wavelengths of light). Targeting about 30 million pre-selected galaxies across one-third of the night sky, scientists will use DESI’s redshifts data to construct 3D maps of the universe. There will be about 10 terabytes (TB) of raw data per year transferred from the observatory to NERSC. After running the data through the pipelines at NERSC (using millions of CPU hours), about 100 TB per year of data products will be made available as data releases approximately once a year throughout DESI’s five years of operations.

    The Large Synoptic Survey Telescope, or LSST, is currently being built on a mountaintop in Chile.

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.


    LSST Data Journey, Illustration by Sandbox Studio, Chicago with Ana Kova

    When completed in 2021, the LSST will take more than 800 panoramic images each night with its 3.2 billion-pixel camera, recording the entire visible sky twice each week. Each patch of sky it images will be visited 1,000 times during the survey, and each of its 30-second observations will be able to detect objects 10 million times fainter than visible with the human eye. A powerful data system will compare new with previous images to detect changes in brightness and position of objects as big as far-distant galaxy clusters and as small as nearby asteroids.

    For these programs, the ExaLearn team will first target large-scale structure simulations of the universe since the field is more developed than others and the scale of the problem size can easily be ramped up to an exascale machine learning challenge.

    As an example of how ExaLearn will advance the field, Nugent said a researcher could run a suite of simulations with the parameters of the universe consisting of 30 percent dark energy and 70 percent dark matter, then a second simulation with 25 percent and 75 percent, respectively. Each of these simulations generates three-dimensional maps of tens of billions of galaxies in the universe and how the cluster and spread apart as time goes by. Using a surrogate model trained on these simulations, the researcher could then quickly run another surrogate model that would generate the output of a simulation in between these values, at 27.5 and 72.5 percent, without needing to run a new, costly simulation — that too would show the evolution of the galaxies in the universe as a function of time. The goal of the ExaLearn software suite is that such results, and their uncertainties and biases, would be a byproduct of the training so that one would know the generated models are consistent with a full simulation.

    Toward this end, Nugent’s team will build on two projects already underway at Berkeley Lab: CosmoFlow and CosmoGAN. CosmoFlow is a deep learning 3D convolutional neural network that can predict cosmological parameters with unprecedented accuracy using the Cori supercomputer at NERSC. CosmoGAN is exploring the use of generative adversarial networks to create cosmological weak lensing convergence maps — maps of the matter density of the universe as would be observed from Earth — at lower computational costs.

    See the full article here .

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    Founded on December 28, 2006, insideHPC is a blog that distills news and events in the world of HPC and presents them in bite-sized nuggets of helpfulness as a resource for supercomputing professionals. As one reader said, we’re sifting through all the news so you don’t have to!

    If you would like to contact me with suggestions, comments, corrections, errors or new company announcements, please send me an email at rich@insidehpc.com. Or you can send me mail at:

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  • richardmitnick 1:32 pm on February 14, 2019 Permalink | Reply
    Tags: , , , , , , , DESI-Dark Energy Spectroscopic Instrument, The Kavli Institute for the Physics and Mathematics of the Universe   

    From The Kavli Institute for the Physics and Mathematics of the Universe: “New Map of Dark Matter Puts the Big Bang Theory on Trial” 

    KavliFoundation

    From The Kavli Institute for the Physics and Mathematics of the Universe

    Kavli IPMU
    Kavli IMPU

    The prevailing view of the universe has just passed a rigorous new test, but the mysteries of dark matter and dark energy remain frustratingly unsolved.

    Dark Matter Research

    Universe map Sloan Digital Sky Survey (SDSS) 2dF Galaxy Redshift Survey

    Scientists studying the cosmic microwave background hope to learn about more than just how the universe grew—it could also offer insight into dark matter, dark energy and the mass of the neutrino.

    Dark matter cosmic web and the large-scale structure it forms The Millenium Simulation, V. Springel et al

    Dark Matter Particle Explorer China

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB deep in Sudbury’s Creighton Mine

    LUX Dark matter Experiment at SURF, Lead, SD, USA

    ADMX Axion Dark Matter Experiment, U Uashington

    A NEW COSMIC MAP was unveiled in August, plotting where the mysterious substance called dark matter is clumped across the universe.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    To immense relief—and frustration—the map is just what scientists had expected. The distribution of dark matter agrees with our current understanding of a universe born with certain properties in a Big Bang, 13.8 billion years ago.

    But for all the map’s confirmatory power, it still tells us little about the true identity of dark matter, which acts as an invisible scaffold for galaxies and cosmic structure. It also does not explain an even bigger factor shaping the cosmos, known as dark energy, an enigmatic force seemingly pushing the universe apart at ever greater speeds. Tantalizingly, however, a small discrepancy between the new findings and previous observations of the early universe might just crack open the door for new physics.

    To discuss these issues, The Kavli Foundation turned to three scientists involved in creating this new cosmic map, compiled by the Dark Energy Survey.

    Adam Hadhazy, Fall 2017

    The participants were:

    SCOTT DODELSON – is a cosmologist and the head of the Department of Physics at Carnegie Mellon University. He is one of the lead scientists behind the Dark Energy Survey’s new map of cosmic structure, which he worked on at the Fermi National Accelerator Laboratory and as a professor at the Kavli Institute for Cosmological Physics at the University of Chicago.

    3
    Map of dark matter made from gravitational lensing measurements of 26 million galaxies in the Dark Energy Survey. The map covers about 1/30th of the entire sky and spans several billion light years in extent. Red regions have more dark matter than average, blue regions less dark matter. Image credit: Chihway Chang/Kavli Institute for Cosmological Physics at the University of Chicago/DES Collaboration.

    RISA WECHSLER – is an associate professor of physics at Stanford University and the SLAC National Accelerator Laboratory, as well as a member of the Kavli Institute for Particle Astrophysics and Cosmology. A founder of the Dark Energy Survey, Wechsler is also involved in two next-generation projects that will delve even deeper into the dark universe.
    GEORGE EFSTATHIOU – is a professor of astrophysics and the former director of the Kavli Institute for Cosmology at the University of Cambridge. Along with his work on the Dark Energy Survey, Efstathiou is a science team leader for the European Space Agency’s Planck spacecraft, which between 2009 and 2013 created a detailed map of the early universe.

    The following is an edited transcript of their roundtable discussion. The participants have been provided the opportunity to amend or edit their remarks.

    THE KAVLI FOUNDATION: The Dark Energy Survey just confirmed that matter as we know it makes up only four percent of the universe. That means 96 percent is stuff we can neither see nor touch, and we have pretty much no idea what it really is. Why are these new findings actually good news?

    RISA WECHSLER: It does seem very strange that the results are good news, right? Forty years ago, nobody would’ve guessed that we apparently live in a universe in which most of the matter is stuff that doesn’t interact with us, and most of the energy is not even matter! It’s still super mind-blowing.

    But we’ve kept making increasingly precise measurements of the universe, and that’s where the Dark Energy Survey results come in. They are the most precise measurements of the density of matter and how it’s clumped in the local universe. In the past, we have measured the density of matter in the young, distant universe. So the Dark Energy Survey is really allowing us to test our understanding of the universe’s evolution, which we’ve formalized as the standard model of Big Bang cosmology, in a totally new way.

    Still, it’s certainly possible that we may have something wrong.

    SCOTT DODELSON: These data, along with precise measurements taken by other projects, might start showing small hints of disagreement, or tension, as we call it, with our current understanding of how the universe began and is now actually expanding at increasing speeds.

    As Risa just said, we’re not sure our current way of thinking is correct because it essentially requires us to make stuff up, namely dark matter and dark energy. It could be that we really are just a month away from a scientific revolution that will upend our whole understanding about cosmology and does not require these things.

    GEORGE EFSTATHIOU: Those measurements of the matter and energy in the young, distant universe that Risa referred to were obtained just a few years ago, when a different program called Planck looked at the relic radiation of the Big Bang, which we call the cosmic microwave background [CMB, see below]. Although the Planck spacecraft’s measurements support the model we’re talking about, one is always uneasy having to postulate things, like dark matter and dark energy, that have not been observed. That’s why the Dark Energy Survey is very important—it can stringently test our knowledge about the birth of the universe by comparing it to the actual structure of the modern-day and young universe.

    TKF: The Dark Energy Survey kicked off four years ago, so you’ve been waiting a long time for these results to come in. What was your initial reaction?

    DODELSON: It was the most amazing experience of my scientific career. On July 7, 2017, a date I will always remember, we had 50 people join a conference call. No one knew what the data were going to say because they were blinded, which guards against accidentally biasing the results to be something you “want” them to be. Then one of the leaders of the lensing analysis, Michael Troxel, ran a computer script on the data, unblinding it, and shared his screen with everybody on the call. We all got to see our results compared to Planck’s. They were in such close agreement, independently of each other. We all just gasped and then clapped.

    WECHSLER: I was on that conference call, too. It was really exciting. I’ve been working on this survey since we wrote the first proposal in 2004, so it felt like a culmination.

    TKF: In 2013, Planck gave us a highly accurate “baby” picture of the universe.

    CMB per ESA/Planck

    ESA/Planck 2009 to 2013

    Now we have a highly precise picture of the universe in a later epoch. George, you were a leader on the Planck mission. What do you see when you look at these two different snapshots in time?

    EFSTATHIOU: The “baby” picture is consistent with a universe mostly made of dark matter and dark energy. It is also consistent with the idea that the universe underwent an exponential expansion in its earliest moments, known as inflation.

    Inflation

    4
    Alan Guth, from Highland Park High School and M.I.T., who first proposed cosmic inflation

    HPHS Owls

    Lambda-Cold Dark Matter, Accelerated Expansion of the Universe, Big Bang-Inflation (timeline of the universe) Date 2010 Credit: Alex MittelmannColdcreation

    Alan Guth’s notes:
    5

    So how does the baby picture extrapolate to the modern, “grown up” universe? As the new Dark Energy Survey results show, the pictures are remarkably consistent.

    DODELSON: We’re all astonished that these two pictures agree to the extent they do. Here’s an example. Let’s say you bought Berkshire Hathaway stock in 1970. Say it was $10 a share then and today it’s $250,000 a share. If you were to predict back then that today it would be $250,000, plus or minus $1,000, people would’ve thought you were nuts. But basically, that’s what we’ve done. When the universe was very young, only 380,000 years old, it was also very “smooth.” Matter was so evenly distributed. Today though—more than 13 billion years later—matter in the cosmos is highly, highly clumped in galaxies, stars, planets and other objects. This is what one would anticipate with cosmic expansion, and with the Dark Energy Survey, we’ve been able to confirm the prediction of this cosmic unevenness to a remarkable degree.

    WECHSLER: What’s really helped us make the precise measurements with Dark Energy Survey is that for the first time, we’re looking over a much larger area, about one-thirtieth, of the sky. That’s three or four times larger than the largest dark matter map we have ever made before. We are also able to make that map essentially over half the age of the universe, from now until about seven billion years ago, by collecting light shining from distant galaxies. So we’re able to tell this story over half of the universe’s history, and it remains consistent throughout.

    There are some small disagreements with the Planck results, but I don’t think we should be too worried yet about them.

    EFSTATHIOU: It would’ve been very interesting if the results had significantly increased the tension with the cosmological standard model, which is the foundation for understanding why, beginning with the Big Bang, the universe is undergoing an accelerated expansion. Some previous surveys had suggested that there might be a problem, though I thought that these results were questionable. In my view, one should rely on the data and not be alarmed if our theories disagree with observations. The universe is what it is.

    TKF: Yet a Nature News story characterized George’s view on the discrepancies as “worrisome.”

    EFSTATHIOU: Well, yes, there have been some claims of tension between the clumping measured in the local universe and Planck’s observations of the distant universe. Some other observations have suggested that the late-time, local universe is expanding at a faster rate than expected from Planck.

    If we were able to say convincingly that there was a real problem posed by any of these individual pieces of data, then we’d have to abandon our standard model of cosmology. We would need new physics, and the sort of physics that we would need would be in the exotic territory, overturning decades of otherwise independently supported physical laws. So it’s a big deal.

    In the past, these sorts of tensions have come and gone. When we wrote the 2013 Planck papers, the results then were in tension with most of astrophysics. Then two years later, some of these tensions had disappeared, and now in 2017, they’ve reemerged. So these things come and go. We need to set a high threshold for our science before launching into explanations based on new physics.

    TKF: It almost sounds like, “if it ain’t broke yet, don’t fix it.”

    EFSTATHIOU: We need to be sure it’s broke before fixing it.

    WECHSLER: I agree with George. There’s a very high bar to show you really understand all of the potential sources of error before taking the big leap of abandoning our current, well-evidenced conception about the universe. I don’t think we’re there yet. It means that we should be really excited about the continuing Dark Energy Survey, as well as all the other upcoming surveys and projects.

    TKF: Indeed, these new results are based on a year’s-worth of measurements out of a total of five years. What might we expect after four more years of data have been crunched?

    WECHSLER: With four times more data, our map of dark matter will be even more precise. I also expect there will be improvements in our analysis methods. There will also be a bunch of other new things that the Dark Energy Survey should discover, including new dwarf galaxies around our Milky Way galaxy that we’ve long thought must be there but couldn’t find. There’s lots more to look forward to!

    DODELSON: The increased precision Risa just talked about will enable us to hit the standard model of cosmology as hard as it’s ever been hit. Disproving the current model will revolutionize the way we think about the universe, so that’s the most exciting thing that I can imagine happening.

    TKF: How are astrophysicists extending the hunt for dark matter and dark energy? Risa, let’s start with you, because you are closely involved in two next-generation “dark universe” projects.

    WECHSLER: With the Dark Energy Spectroscopic Instrument, or DESI [pronounced “DEZ-ee”], we’ll be getting what we call spectra, or detailed observations of the light from about 35 million galaxies and quasars, which are galaxies that appear extra bright because their central black holes are actively devouring matter.

    LBNL/DESI spectroscopic instrument on the Mayall 4-meter telescope at Kitt Peak National Observatory starting in 2018

    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA, Altitude 2,120 m (6,960 ft)

    Kitt Peak National Observatory of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers 55 mi west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft)

    That’s about 10 times more spectra data than we’ve collected from all instruments, so you can imagine that will be really transformative. With DESI, we will be able to independently measure the universe’s expansion rate and how fast its structure of matter and dark matter grow, both of which are influenced by dark energy. Then when you compare those measurements, you get a precise test of the physics governing the universe. DESI will start in 2019 using a telescope in Arizona.

    The other major new instrument I’m working on is the Large Synoptic Survey Telescope, LSST.

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    It will make observations just like the Dark Energy Survey, but at substantially higher precision. In fact, it will cover about four times more area, and the billions of galaxies it sees will be much deeper and farther away. LSST will be a new observatory, being built in Chile right now, and it’s scheduled to begin in about 2022.

    DODELSON: My guess is that both projects will raise new scientific questions. We’ve already seen that with the Dark Energy Survey. Questions shift over time and evolve, so I’m not sure we know what the most exciting thing we’re going to learn from LSST or DESI is.

    EFSTATHIOU: One of my hopes for Planck was that the standard model of cosmology would break and it didn’t. But wouldn’t it be absolutely great for cosmology and for physics if this happened? So we should plug away and see. Maybe we’ll be lucky.

    TKF: If you had to place a bet on what dark matter and dark energy actually are, where would you put your chips?

    DODELSON: We’re living in an era of cognitive dissonance. There is all this cosmological evidence for the existence of dark matter, but over the last 30 years, we’ve run all these experiments and haven’t found it. My bet is that we’re looking at things all wrong. Someone who’s 8 years old today is going to come around and figure out how to make sense of all the data without evoking mysterious new substances.

    EFSTATHIOU: What odds are you giving on that, Scott?

    DODELSON: I’m betting $2,000 of George’s money. [Laughter]

    EFSTATHIOU: I wouldn’t put a bet on any specific candidate for the dark matter. But I bet that dark energy is the cosmological constant, a fudge factor invented by Einstein describing the density of energy in a vacuum.

    WECHSLER: I’m basically with George on this one. I think if Scott’s right, that’ll be wonderful—but that definitely isn’t where I would place my money.

    I think it’s very likely that 15 years from now, we will just then be measuring that dark energy is caused by this cosmological constant. We will be able to shrink the error bars and find that our present model still works.

    On dark matter, I think it’s much less clear. For a long time, the most popular candidate was this thing called the WIMP, or a Weakly Interacting Massive Particle. That idea is still popular and totally possible, but a lot of the particles that could be that kind of dark matter are already ruled out. The other really compelling candidate is a subatomic particle called the axion. People are just getting to a place where they’re able to start searching for these particles that we think are going to be extremely difficult to detect. It’s also possible that dark matter might surprise us, that it’s some new kind of particle that we don’t have the techniques to look for yet.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Kavli IPMU (Kavli Institute for the Physics and Mathematics of the Universe) is an international research institute with English as its official language. The goal of the institute is to discover the fundamental laws of nature and to understand the Universe from the synergistic perspectives of mathematics, astronomy, and theoretical and experimental physics. The Institute for the Physics and Mathematics of the Universe (IPMU) was established in October 2007 under the World Premier International Research Center Initiative (WPI) of the Ministry of Education, Sports, Science and Technology in Japan with the University of Tokyo as the host institution. IPMU was designated as the first research institute within the University of Tokyo Institutes for Advanced Study (UTIAS) in January 2011. It received an endowment from The Kavli Foundation and was renamed the “Kavli Institute for the Physics and Mathematics of the Universe” in April 2012. Kavli IPMU is located on the Kashiwa campus of the University of Tokyo, and more than half of its full-time scientific members come from outside Japan. http://www.ipmu.jp/
    The Kavli Foundation, based in Oxnard, California, is dedicated to the goals of advancing science for the benefit of humanity and promoting increased public understanding and support for scientists and their work.

    The Foundation’s mission is implemented through an international program of research institutes, professorships, and symposia in the fields of astrophysics, nanoscience, neuroscience, and theoretical physics as well as prizes in the fields of astrophysics, nanoscience, and neuroscience.

     
  • richardmitnick 9:20 am on August 14, 2018 Permalink | Reply
    Tags: , , , , , DECam at the Blanco telescope, DESI-Dark Energy Spectroscopic Instrument, ,   

    From Fermi National Accelerator Lab: “Mapping the universe in 3-D: Fermilab contributes to the Dark Energy Spectroscopic Instrument” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

    From Fermi National Accelerator Lab , an enduring source of strength for the US contribution to scientific research world wide.

    August 13, 2018
    Jordan Rice

    In 1998, scientists discovered that the universe’s expansion is accelerating. Physicists don’t know how or why the universe is accelerating outward, but they gave the mysterious force behind this phenomenon a name: dark energy.

    Scientists know a great deal about the effects of dark energy, but they don’t know what it is. Cosmologists approximate that 68 percent of the universe’s total energy must be made of the stuff. One way to get a better handle on dark energy and its effects is to create detailed maps of the universe, plotting its expansion. Scientists, engineers and technicians are currently building the Dark Energy Spectroscopic Instrument, or DESI, to do just that.

    DESI will help create the largest 3-D map of galaxies to date, one that will span a third of the entire sky, stretch back 11 billion light-years, and record approximately 35 million galaxies and quasars.

    LBNL/DESI Dark Energy Spectroscopic Instrument for the Nicholas U. Mayall 4-meter telescope at Kitt Peak National Observatory near Tucson, Ariz, USA

    It will measure the spectra of light emanating from galaxies to determine their distances from Earth. Other surveys have created maps that locate galaxies’ lateral positions in the sky, but scientists using DESI will be able to take more precise measurements of their distance from us, creating high-resolution, 3-D maps.

    DESI is currently being installed at the Mayall 4-Meter Telescope at Kitt Peak National Observatory in Tucson, Arizona. Once installation is complete, it will run for five years.


    Mayall telescope interior

    NOAO/Mayall 4 m telescope at Kitt Peak, Arizona, USA, Altitude 2,120 m (6,960 ft)

    The DESI project is managed at the U.S. Department of Energy’s Lawrence Berkley National Laboratory (Berkeley Lab) in California, and the U.S. DOE’s Fermilab is contributing to the ambitious effort with specialty systems for collecting and analyzing the galactic light.

    “The collaborative effort to build DESI is an example of how science draws on expertise from multiple institutions toward a common goal, one that humanity is always moving toward: understanding the fundamentals of our universe,” said Berkeley Lab’s Michael Levi, DESI project director.

    One of the largest pieces Fermilab is contributing is the DESI corrector barrel. Fermilab collaborators designed, built and tested the barrel, which is roughly the size of a telephone booth. It plays a critical role: holding DESI’s six giant lenses in perfect alignment. To ensure spot-on precision, the barrel is designed so that the lenses are accurately positioned to within the width of a human hair. Collaborators at University College London recently finished installing the lenses in the barrel, and the whole ensemble will soon be lifted onto the telescope.

    “The barrel needs to be extremely precise,” said Gaston Gutierrez, Fermilab scientist managing the corrector barrel construction. “If there is any misalignment of the lenses, the error will be highly magnified, and the images will be blurred.”

    Fermilab also designed and built large structures that will support a cage surrounding the barrel. These were delivered to the Mayall in April, and their installation has begun.

    To convert the light from galaxies into digital information for analysis, DESI will use high-tech versions of the familiar components in typical hand-held cameras — charge coupled devices, or CCDs. Fermilab packaged and tested these sensitive devices before delivering them to Tucson.

    The job of collecting the galactic light belongs to DESI’s 5,000 fiber-optic cables, which will help record the spectra of each galaxy. For roughly 20 minutes, each one of the fibers will aim at a single galaxy and record its spectrum. Then the telescope will move to a new position in the sky, and all 5,000 fibers will be moved to point at new galaxies. Fermilab is developing the software that tells the instrument where in the sky to point those fibers. Without this automation, DESI would not be able to measure the millions of objects it plans to study.

    To fully understand the spectra that DESI will collect, scientists need to keep detailed information about the instrument and telescope status. In addition to the DESI barrel, Fermilab is creating an electronic logbook and a database to store the instrument control systems operational data. These will be used to keep track of the information on the systems required to operate DESI, such as how to read the CCDs, direct the telescope and ensure the apparatus for recording the spectra is working properly.

    2
    Fermilab is developing the software that tells DESI where in the sky to point its 5,000 fiber-optic cables, a fraction of which are shown here. Photo: Lawrence Berkeley National Laboratory

    DESI’s predecessor, called the Dark Energy Camera (DECam), is currently mounted on Chile’s Victor Blanco telescope, the sister telescope of the Mayall.

    Dark Energy Survey


    Dark Energy Camera [DECam], built at FNAL


    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    In 2012, researchers and technicians completed DECam’s construction for use in the five-year Dark Energy Survey, hosted by Fermilab. The same scientists who designed DECam are bringing their expertise and knowledge to DESI.

    The Dark Energy Survey and DECam serve as stepping stones to DESI. The DESI project will improve our understanding of the nature of dark energy by using the Dark Energy Survey’s results as a baseline. DECam’s data will also help DESI find the galaxies so the latter can take more precise spectra measurements to determine the galaxy’s redshift: The farther away a galaxy is from us, the more its light is stretched and shifted in the direction of redder (longer) wavelengths, by the expansion of the universe.

    “For the Dark Energy Survey, we are just taking images, but for DESI we are pointing fibers at galaxies and measuring spectra,” said Fermilab’s Brenna Flaugher, project manager of DES and one of the leading scientists for DESI. “So, it is sort of the next level of resolution in redshift.”

    DESI’s final pieces are planned to be installed by April 2019, with first light planned for May of that year.

    “DESI will help us understand the nature of dark energy,” Flaugher said. “And that will lead to a better understanding of the evolution of our universe.”

    Work on DESI is supported by DOE’s Office of Science along with several international partners.

    See the full article here .


    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    FNAL Icon

    Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a US Department of Energy national laboratory specializing in high-energy particle physics. Fermilab is America’s premier laboratory for particle physics and accelerator research, funded by the U.S. Department of Energy. Thousands of scientists from universities and laboratories around the world
    collaborate at Fermilab on experiments at the frontiers of discovery.


    FNAL/MINERvA

    FNAL DAMIC

    FNAL Muon g-2 studio

    FNAL Short-Baseline Near Detector under construction

    FNAL Mu2e solenoid

    Dark Energy Camera [DECam], built at FNAL

    FNAL DUNE Argon tank at SURF

    FNAL/MicrobooNE

    FNAL Don Lincoln

    FNAL/MINOS

    FNAL Cryomodule Testing Facility

    FNAL Minos Far Detector

    FNAL LBNF/DUNE from FNAL to SURF, Lead, South Dakota, USA

    FNAL/NOvA experiment map

    FNAL NOvA Near Detector

    FNAL ICARUS

    FNAL Holometer

     
  • richardmitnick 12:27 pm on December 14, 2017 Permalink | Reply
    Tags: , , , Bright Galaxy Survey, , Dark matter mock-ups, DESI-Dark Energy Spectroscopic Instrument, Jülich Supercomputer Center in Germany, , Mock galaxies catalog,   

    From LBNL: “Creating a World of Make-Believe to Better Understand the Real Universe” 

    Berkeley Logo

    Berkeley Lab

    December 14, 2017
    Glenn Roberts Jr.
    geroberts@lbl.gov
    (510) 486-5582

    1
    This plot shows a thin slice through a mock galaxies catalog. The blue and green points are “bright” and “faint” galaxies simulated for the Dark Energy Spectroscopic Instrument’s Bright Galaxy Survey, and the red points show galaxies that are brighter than the magnitude limit of the Sloan Digital Sky Survey, a predecessor sky survey. (Credit: Alex Smith/Durham University)

    SDSS Telescope at Apache Point Observatory, NM, USA, Altitude 2,788 meters (9,147 ft)

    Seeing is believing, or so the saying goes.

    And in some cases, a world of make-believe can help you realize what you’re actually seeing, too.

    Scientists are creating simulated universes, for example – complete with dark matter mock-ups, computer-generated galaxies, quasi quasars, and pseudo supernovae ­– to better understand real-world observations.

    Their aim is to envision how new Earth-based and space-based sky surveys will see the universe, and to help analyze and interpret the vast treasure troves of data that these surveys will amass.

    “We want to be able to hit the ground running once we get real data,” said Stephen Bailey, a physicist at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) who is the technical lead and manager of data systems for a 3-D sky-mapping project known as the Dark Energy Spectroscopic Instrument, or DESI, that is slated to begin observing in 2019.

    LBNL/DESI spectroscopic instrument on the Mayall 4-meter telescope at Kitt Peak National Observatory starting in 2018

    Several DESI teams are building out separate simulations populated with the many types of objects DESI will encounter. “What is this going to look like for DESI?” Bailey asked. “What is the actual spectra, or light signature, that DESI is going to observe? We have to make sure the mock objects have the right colors and chemical abundances.”

    John Moustakas, an assistant professor of physics at Siena College in New York who is also working on the simulations for DESI, added, “And that’s challenging because nothing like DESI exists.”

    The computerized models are informed by observations from previous surveys and by large-scale simulations of the universe that account for complex physics including dark matter, an unknown form of matter that, together with dark energy, makes up about 95 percent of the total mass and energy in the universe.

    “To the greatest extent possible, the simulations are based on models of real objects – from pulling out all of these pieces from other surveys,” Moustakas said. “Perhaps in a perfect world these would be purely theoretical models, but we don’t understand galaxies well enough to be able to do that.”

    And even though there is data from previous surveys, DESI will see the sky in a different way. “You have to extract out all the instrument parts of all these other surveys to get to: ‘This is what other galaxies look like, intrinsically,’” he said. Next, he said, scientists must figure out how DESI’s unique set of instruments will see them.

    The simulated objects and universes created and refined using powerful supercomputers, including Berkeley Lab’s National Energy Research Scientific Computing Center (NERSC), must ultimately take into account the Earth’s atmospheric noise, and weather and lighting conditions including the phases of the moon, which all affect observations.

    NERSC Cray XC40 Cori II supercomputer

    LBL NERSC Cray XC30 Edison supercomputer


    The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.

    NERSC PDSF


    PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

    DESI will operate from the Nicholas U. Mayall 4-Meter Telescope at Kitt Peak National Observatory in Arizona. It will measure the light from tens of millions of galaxies and other objects with a carefully choreographed array of 5,000 swiveling robots – each pointing a fiber-optic cable at a targeted space object. The robotic array will cycle through a sequence of objects, peering up to 11 billion years back in the history of our universe.

    The light captured by DESI will provide precise measurements that will help scientists to retrace the evolution of the universe and learn more about dark energy, which is responsible for the universe’s mysterious, accelerating expansion. Berkeley Lab is the lead lab for the DESI project, and the collaboration now involves about 200 scientists at 40 institutions.

    Alex Smith, a graduate student at Durham University in England and a DESI collaboration member, worked with a team to develop a mock catalog of galaxies for DESI that taps into a powerful simulation of how the universe’s matter has evolved over the past 13 billion years.

    Carried out at the Jülich Supercomputer Center in Germany, this Millennium-XXL simulation used 12,000 computer cores – the equivalent to about 300 years’ worth of computer processing time.

    Jülich Supercomputing Centre in Jülich, Germany

    It generated about 100 terabytes of data, which is nearly as much data as the Hubble Space Telescope transmitted in space images during its first 24 years of operation.

    The mock galaxy catalog that Smith’s team developed focused on the same one-third of the sky that DESI will survey. The catalog shows how galaxies’ clustering and ‘redshift’ – the color based on their distance and movement away from us – changes over time and will likely appear to DESI.

    Due to cosmic expansion, very distant objects appear redder and fainter. Earlier mock catalogs had not accounted for these changes in redshift, Smith said.

    “It’s important to have mock catalogs that have realistic properties – that look similar to how we think the actual survey is going to look,” he added.

    5
    The predicted galaxy distribution in the Millennium XXL simulation. (Click image for larger view.) Each galaxy is represented by a sphere whose intensity and size are related to the expected total mass in stars and the size of its cold gas disk. (Credit: Max-Planck-Institute for Astrophysics)

    His team’s survey used a method known as halo occupation distribution, or HOD, to model the average number of galaxies and their brightness based on the Millennium-XXL survey’s detailed simulations of the distribution of dark matter. In dark matter models, matter forms within clumps of dark matter known as halos, and galaxies are enveloped by these halos.

    Smith noted that the distribution of galaxies within these halos, and other properties incorporated in the latest catalog, are taken from data collected in past surveys, including the Sloan Digital Sky Survey and the Galaxy and Mass Assembly Survey.

    The galaxies in the catalog are simplified to their brightness, as it will appear in one of the wavelength bands that DESI will be scanning. The mock catalog is also intended to simulate the type of galaxies that will be targeted during sky conditions that favor brighter objects, such as those that exist around the times of sunrises and sunsets, or when the moon is brighter in the sky, for example. Separate simulations will account for darker viewing conditions.

    “The mock catalog I created assumes you can observe everything with perfect precision,” Smith noted, so additional properties will need to be added to simulate weather and other effects. The DESI collaboration has access to a decade of weather statistics collected at the Kitt Peak National Observatory, Bailey said.

    Even after the start of DESI’s survey, collaboration scientists will continue to adapt and improve the models.

    6
    A view of some candidate targets for DESI obervations is shown here, along with overlay images showing mock spectra, or light signatures, generated in the planning stages for DESI. (Credit: legacysurvey.org, John Moustakas, DESI collaboration)

    “There is a learning component to it,” Moustakas said. “As we start to observe things, we will then use those targeted objects to build better models of what those objects are.”

    Relying too much on simulations can also be a problem, DESI scientists noted, so observations will provide a needed reality check. For example, superbright objects called quasars, which are among the targets for DESI, have been particularly difficult to simulate.

    “You don’t want to believe your simulations too much, because nature is much harsher,” Moustakas said.

    Bailey added, “We are currently bootstrapping off other experiments; then we’ll be bootstrapping off ourselves.”

    Smith noted that to prepare for ever-larger surveys, there will be a need for more detailed and accurate models to home in on the nature of dark energy and gravity, for example.

    “To be able to make cosmological measurements at the required high precision to be able to tell all of these viable models apart, it’s really important to have more and more realistic mock catalogs,” he said.

    NERSC is a DOE Office of Science User Facility.

    DESI is supported by the U.S. Department of Energy’s Office of High Energy Physics; the U.S. National Science Foundation, Division of Astronomical Sciences under contract to the National Optical Astronomy Observatory; the Science and Technologies Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the National Council of Science and Technology of Mexico; the Ministry of Economy of Spain; and DESI member institutions. The DESI scientists are honored to be permitted to conduct astronomical research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation.

    Current DESI Member Institutions include: Aix-Marseille University; Argonne National Laboratory; Barcelona-Madrid Regional Participation Group; Brookhaven National Laboratory; Boston University; Carnegie Mellon University; CEA-IRFU, Saclay; China Participation Group; Cornell University; Durham University; École Polytechnique Fédérale de Lausanne; Eidgenössische Technische Hochschule, Zürich; Fermi National Accelerator Laboratory; Granada-Madrid-Tenerife Regional Participation Group; Harvard University; Korea Astronomy and Space Science Institute; Korea Institute for Advanced Study; Institute of Cosmological Sciences, University of Barcelona; Lawrence Berkeley National Laboratory; Laboratoire de Physique Nucléaire et de Hautes Energies; Mexico Regional Participation Group; National Optical Astronomy Observatory; Siena College; SLAC National Accelerator Laboratory; Southern Methodist University; Swinburne University; The Ohio State University; Universidad de los Andes; University of Arizona; University of California, Berkeley; University of California, Irvine; University of California, Santa Cruz; University College London; University of Michigan at Ann Arbor; University of Pennsylvania; University of Pittsburgh; University of Portsmouth; University of Queensland; University of Rochester; University of Toronto; University of Utah; University of Zurich; UK Regional Participation Group; Yale University. For more information, visit desi.lbl.gov.

    The National Optical Astronomy Observatory (NOAO) is the national center for ground-based nighttime astronomy in the United States (www.noao.edu) and is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation Division of Astronomical Sciences.

    Established in 2007 by Mark Heising and Elizabeth Simons, the Heising-Simons Foundation (www.heisingsimons.org) is dedicated to advancing sustainable solutions in the environment, supporting groundbreaking research in science, and enhancing the education of children.

    The Gordon and Betty Moore Foundation, established in 2000, seeks to advance environmental conservation, patient care and scientific research. The Foundation’s Science Program aims to make a significant impact on the development of provocative, transformative scientific research, and increase knowledge in emerging fields. For more information, visit http://www.moore.org.

    The Science and Technology Facilities Council (STFC) of the United Kingdom coordinates research on some of the most significant challenges facing society, such as future energy needs, monitoring and understanding climate change, and global security. It offers grants and support in particle physics, astronomy and nuclear physics, visit http://www.stfc.ac.uk.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    A U.S. Department of Energy National Laboratory Operated by the University of California

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