Tagged: DES – Dark Energy Survey Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 2:46 pm on August 14, 2017 Permalink | Reply
    Tags: , , , , DES - Dark Energy Survey, LAE-Lyman alpha emission, , The fog was already lifting when the universe was 5% of its current age   

    From NOAO: “Distant Galaxies ‘Lift the Veil’ on the End of the Cosmic Dark Ages” 

    NOAO Banner

    July 11, 2017

    Dr. Junxian Wang
    Department of Astronomy
    University of Science and Technology of China
    96 Jinzhai Road Hefei, Anhui 230026 China
    jxw@ustc.edu.cn

    Dr. Sangeeta Malhotra
    ASU School of Earth and Space Exploration
    and
    Astrophysics Science Division,
    Goddard Space Flight Center
    8800 Greenbelt Road
    Greenbelt, Maryland 20771
    sangeeta.malhotra@asu.edu

    1
    False color image of a 2 square degree region of the LAGER survey field, created from images taken in the optical at 500 nm (blue), in the near-infrared at 920 nm (red), and in a narrow-band filter centered at 964 nm (green). The last is sensitive to hydrogen Lyman alpha emission at z ~ 7. The small white boxes indicate the positions of the 23 LAEs discovered in the survey. The detailed insets (yellow) show two of the brightest LAEs; they are 0.5 arcminutes on a side, and the white circles are 5 arcseconds in diameter. Image Credit: Zhen-Ya Zheng (SHAO) & Junxian Wang (USTC).

    Astronomers studying the distant Universe have found that small star-forming galaxies were abundant when the Universe was only 800 million years old, a few percent of its present age. The results suggest that the earliest galaxies, which illuminated and ionized the Universe, formed at even earlier times.

    Long ago, about 300,000 years after the beginning of the Universe (the Big Bang), the Universe was dark. There were as yet no stars and galaxies, and the Universe was filled with neutral hydrogen gas. At some point the first galaxies appeared, and their energetic radiation ionized their surroundings, the intergalactic gas, illuminating and transforming the Universe.

    2

    While this dramatic transformation is known to have occurred sometime in the interval between 300 million years and 1 billion years after the Big Bang, determining when the first galaxies formed is a challenge. The intergalactic gas, which is initially neutral, strongly absorbs and scatters the ultraviolet light emitted by the galaxies, making them difficult to detect.

    To home in on when the transformation occurred, astronomers take an indirect approach. Using the demographics of small star-forming galaxies to determine when the intergalactic gas became ionized, they can infer when the ionizing sources, the first galaxies, formed. If star forming galaxies, which glow in the light of the hydrogen Lyman alpha line, are surrounded by neutral hydrogen gas, the Lyman alpha photons are readily scattered, much like headlights in fog, obscuring the galaxies. When the gas is ionized, the fog lifts, and the galaxies are easier to detect.

    A new study taking this approach has discovered 23 candidate Lyman alpha emitting galaxies (LAEs) that were present 800 million years after the Big Bang (at a redshift of z~7), the largest sample detected to date at that epoch. The study, “Lyman-Alpha Galaxies in the Epoch of Reionization” (LAGER), was carried out by an international team of astronomers from China, the US, and Chile using the Dark Energy Camera (DECam) on the CTIO 4-m Blanco telescope.

    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

    While the study detected many LAEs, it also found that LAEs were 4 times less common at 800 million years than they were a short time later, at 1 billion years (at a redshift of z~5.7). The results imply that the process of ionizing the Universe began early and was still incomplete at 800 million years, with the intergalactic gas about half neutral and half ionized at that epoch. The low incidence rate of LAEs at 800 million years results from the suppression of their Lyman alpha emission by neutral intergalactic gas.

    The study shows that “the fog was already lifting when the universe was 5% of its current age”, explained Sangeeta Malhotra (Goddard Space Flight Center and Arizona State University), one of the co-leads of the survey.

    Junxian Wang (USTC), the organizer of the study, further explained, “Our finding that the intergalactic gas is 50% ionized at z ~ 7 implies that a large fraction of the first galaxies that ionized and illuminated the universe formed early, less than 800 million years after the Big Bang.”

    For Zhenya Zheng (Shanghai Astronomical Observatory, CAS), the lead author of the paper describing these results, “800 million years is the current frontier in reionization studies.” While hundreds of LAEs have been found at later epochs, only about two dozen candidate LAEs were known at 800 million years prior to the current study. The new results dramatically increase the number of LAEs known at this epoch.

    “None of this science would have been possible without the widefield capabilities of DECam and its community pipeline for data reduction,” remarked coauthor James Rhoads. “These capabilities enable efficient surveys and thereby the discovery of faint galaxies as well as rare, bright ones.”

    To build on these results, the team is “continuing the search for distant star forming galaxies over a larger volume of the Universe”, said Leopoldo Infante (Pontificia Catolica University of Chile and the Carnegie Institution for Science), “to study the clustering of LAEs.” Clustering provides unique insights into how the fog lifts. The team is also investigating the nature of these distant galaxies.

    Reference:
    First Results from the Lyman Alpha Galaxies in the Epoch of Reionization (LAGER) Survey: Cosmological Reionization at z ~ 7, Zhenya Zheng et al. 2017, Astrophysical Journal Letters, 842, 22.
    Preprint: https://arxiv.org/abs/1703.02985

    See the full article here .

    Please help promote STEM in your local schools.
    STEM Icon

    Stem Education Coalition

    NOAO News
    NOAO is the US national research & development center for ground-based night time astronomy. In particular, NOAO is enabling the development of the US optical-infrared (O/IR) System, an alliance of public and private observatories allied for excellence in scientific research, education and public outreach.

    Our core mission is to provide public access to qualified professional researchers via peer-review to forefront scientific capabilities on telescopes operated by NOAO as well as other telescopes throughout the O/IR System. Today, these telescopes range in aperture size from 2-m to 10-m. NOAO is participating in the development of telescopes with aperture sizes of 20-m and larger as well as a unique 8-m telescope that will make a 10-year movie of the Southern sky.

    In support of this mission, NOAO is engaged in programs to develop the next generation of telescopes, instruments, and software tools necessary to enable exploration and investigation through the observable Universe, from planets orbiting other stars to the most distant galaxies in the Universe.

    To communicate the excitement of such world-class scientific research and technology development, NOAO has developed a nationally recognized Education and Public Outreach program. The main goals of the NOAO EPO program are to inspire young people to become explorers in science and research-based technology, and to reach out to groups and individuals who have been historically under-represented in the physics and astronomy science enterprise.

    The National Optical Astronomy Observatory is proud to be a US National Node in the International Year of Astronomy, 2009.

    About Our Observatories:
    Kitt Peak National Observatory (KPNO)

    Kitt Peak

    Kitt Peak National Observatory (KPNO) has its headquarters in Tucson and operates the Mayall 4-meter, the 3.5-meter WIYN , the 2.1-meter and Coudé Feed, and the 0.9-meter telescopes on Kitt Peak Mountain, about 55 miles southwest of the city.

    Cerro Tololo Inter-American Observatory (CTIO)

    NOAO Cerro Tolo

    The Cerro Tololo Inter-American Observatory (CTIO) is located in northern Chile. CTIO operates the 4-meter, 1.5-meter, 0.9-meter, and Curtis Schmidt telescopes at this site.

    The NOAO System Science Center (NSSC)

    Gemini North
    Gemini North

    Gemini South telescope
    Gemini South

    The NOAO System Science Center (NSSC) at NOAO is the gateway for the U.S. astronomical community to the International Gemini Project: twin 8.1 meter telescopes in Hawaii and Chile that provide unprecendented coverage (northern and southern skies) and details of our universe.

    NOAO is managed by the Association of Universities for Research in Astronomy under a Cooperative Agreement with the National Science Foundation.

    Advertisements
     
  • richardmitnick 4:41 pm on August 4, 2017 Permalink | Reply
    Tags: , , , CMU-Carnegie Mellon University, , , DES - Dark Energy Survey, Scott Dodelson   

    From CMU: “Scott Dodelson Appointed Head of Department of Physics” 

    Carnegie Mellon University logo
    Carnegie Mellon University

    [It is rare that I would post about such an appointment. But Scott Dodelson is a rare bird.]
    [This post is dedicated to J.L.T. Jack, keep your eye on this guy and CMU.]

    August 3, 2017
    Jocelyn Duffy

    1
    Scott Dodelson

    Renowned physicist Scott Dodelson has been named the head of the Department of Physics in Carnegie Mellon University’s Mellon College of Science.

    Dodelson conducts research at the interface between particle physics and cosmology, examining the phenomena of dark energy, dark matter, inflation and cosmological neutrinos.

    He is the co-chair of the Science Committee for the Dark Energy Survey (DES), an international collaboration that aims to map hundreds of millions of galaxies, detect thousands of supernovae and find patterns of cosmic structure in an attempt to reveal the nature of dark energy.

    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

    On Aug. 3, the DES released results that measured the structure of the universe to the highest level of precision yet.

    Dodelson also works with the South Pole Telescope and the Large Synoptic Survey Telescope (LSST).

    South Pole Telescope

    The South Pole Telescope studies the Cosmic Microwave Background to gain a better understanding of inflation, dark energy and neutrinos. The LSST, which is currently being built in Chile, will survey the sky for a decade, creating an enormous data set that will help scientists determine the properties of dark energy and dark matter and the composition and history of our solar system.

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction 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.

    Dodelson was attracted to CMU in part by the physics department’s varied areas of strength and the leadership role the department’s McWilliams Center for Cosmology and its faculty play in a number of large, international cosmological surveys, including LSST and the Sloan Digital Sky Survey.

    “Within the McWilliams Center, I found kindred spirits in the faculty who are leading scientific projects aimed at understanding the universe, but I was equally attracted to the department’s strong groups in biological physics, condensed matter and nuclear and particle physics,” said Dodelson. “I’m excited to learn about these diverse fields and connect with other departments throughout the university.”

    Under Dodelson’s leadership, the physics department will partner with other departments within the Mellon College of Science through a new theory center and continue to collaborate with colleagues in statistics, computer science and engineering. Dodelson also hopes to increase the department’s partnerships with other universities and research initiatives worldwide and bring physics to the community through outreach programs.

    “I was drawn by the university’s enthusiasm for foundational research,” Dodelson said. “The physics department will strive to bring this excitement to students, alumni and the broader community.”

    Dodelson comes to Carnegie Mellon from the Fermi National Accelerator Laboratory (Fermilab), where he was a distinguished scientist, and the University of Chicago where he was a professor in the Department of Astronomy and Astrophysics and Kavli Institute for Cosmological Physics. While at Fermilab, Dodelson served as head of the Theoretical Astrophysics Group and co-founder and interim director of the Center for Particle Astrophysics.

    Dodelson earned a joint B.A./B.S. degree in applied physics and a Ph.D. in theoretical physics from Columbia University. He completed a post-doctoral fellowship at Harvard University.

    Dodelson will assume the position of department head from Stephen Garoff who has served as head since 2013.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Carnegie Mellon Campus

    Carnegie Mellon University (CMU) is a global research university with more than 12,000 students, 95,000 alumni, and 5,000 faculty and staff.
    CMU has been a birthplace of innovation since its founding in 1900.
    Today, we are a global leader bringing groundbreaking ideas to market and creating successful startup businesses.
    Our award-winning faculty members are renowned for working closely with students to solve major scientific, technological and societal challenges. We put a strong emphasis on creating things—from art to robots. Our students are recruited by some of the world’s most innovative companies.
    We have campuses in Pittsburgh, Qatar and Silicon Valley, and degree-granting programs around the world, including Africa, Asia, Australia, Europe and Latin America.

     
  • richardmitnick 4:21 pm on August 4, 2017 Permalink | Reply
    Tags: , , , , , DES - Dark Energy Survey, , ,   

    From Quanta: “Scientists Unveil a New Inventory of the Universe’s Dark Contents” 

    Quanta Magazine
    Quanta Magazine

    August 3, 2017
    Natalie Wolchover

    In a much-anticipated analysis of its first year of data, the Dark Energy Survey (DES) telescope experiment has gauged the amount of dark energy and dark matter in the universe by measuring the clumpiness of galaxies — a rich and, so far, barely tapped source of information that many see as the future of cosmology.

    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

    The analysis, posted on DES’s website today and based on observations of 26 million galaxies in a large swath of the southern sky, tweaks estimates only a little. It draws the pie chart of the universe as 74 percent dark energy and 21 percent dark matter, with galaxies and all other visible matter — everything currently known to physicists — filling the remaining 5 percent sliver.

    The results are based on data from the telescope’s first observing season, which began in August 2013 and lasted six months. Since then, three more rounds of data collection have passed; the experiment begins its fifth and final planned observing season this month. As the 400-person team analyzes more of this data in the coming years, they’ll begin to test theories about the nature of the two invisible substances that dominate the cosmos — particularly dark energy, “which is what we’re ultimately going after,” said Joshua Frieman, co-founder and director of DES and an astrophysicist at Fermi National Accelerator Laboratory (Fermilab) and the University of Chicago. Already, with their first-year data, the experimenters have incrementally improved the measurement of a key quantity that will reveal what dark energy is.

    Both terms — dark energy and dark matter — are mental place holders for unknown physics. “Dark energy” refers to whatever is causing the expansion of the universe to accelerate, as astronomers first discovered it to be doing in 1998. And great clouds of missing “dark matter” have been inferred from 80 years of observations of their apparent gravitational effect on visible matter (though whether dark matter consists of actual particles or something else, nobody knows).

    The balance of the two unknown substances sculpts the distribution of galaxies. “As the universe evolves, the gravity of dark matter is making it more clumpy, but dark energy makes it less clumpy because it’s pushing galaxies away from each other,” Frieman said. “So the present clumpiness of the universe is telling us about that cosmic tug-of-war between dark matter and dark energy.”

    2
    The Dark Energy Survey uses a 570-megapixel camera mounted on the Victor M. Blanco Telescope in Chile (left). The camera is made out of 74 individual light-gathering wafers.

    A Dark Map

    Until now, the best way to inventory the cosmos has been to look at the Cosmic Microwave Background [CMB]: pristine light from the infant universe that has long served as a wellspring of information for cosmologists, but which — after the Planck space telescope mapped it in breathtakingly high resolution in 2013 — has less and less to offer.

    CMB per ESA/Planck

    ESA/Planck

    Cosmic microwaves come from the farthest point that can be seen in every direction, providing a 2-D snapshot of the universe at a single moment in time, 380,000 years after the Big Bang (the cosmos was dark before that). Planck’s map of this light shows an extremely homogeneous young universe, with subtle density variations that grew into the galaxies and voids that fill the universe today.

    Galaxies, after undergoing billions of years of evolution, are more complex and harder to glean information from than the cosmic microwave background, but according to experts, they will ultimately offer a richer picture of the universe’s governing laws since they span the full three-dimensional volume of space. “There’s just a lot more information in a 3-D volume than on a 2-D surface,” said Scott Dodelson, co-chair of the DES science committee and an astrophysicist at Fermilab and the University of Chicago.

    To obtain that information, the DES team scrutinized a section of the universe spanning an area 1,300 square degrees wide in the sky — the total area of 6,500 full moons — and stretching back 8 billion years (the data were collected by the half-billion-pixel Dark Energy Camera mounted on the Victor M. Blanco Telescope in Chile). They statistically analyzed the separations between galaxies in this cosmic volume. They also examined the distortion in the galaxies’ apparent shapes — an effect known as “weak gravitational lensing” that indicates how much space-warping dark matter lies between the galaxies and Earth. These two probes — galaxy clustering and weak lensing — are two of the four approaches that DES will eventually use to inventory the cosmos. Already, the survey’s measurements are more precise than those of any previous galaxy survey, and for the first time, they rival Planck’s.

    4

    “This is entering a new era of cosmology from galaxy surveys,” Frieman said. With DES’s first-year data, “galaxy surveys have now caught up to the cosmic microwave background in terms of probing cosmology. That’s really exciting because we’ve got four more years where we’re going to go deeper and cover a larger area of the sky, so we know our error bars are going to shrink.”

    For cosmologists, the key question was whether DES’s new cosmic pie chart based on galaxy surveys would differ from estimates of dark energy and dark matter inferred from Planck’s map of the cosmic microwave background. Comparing the two would reveal whether cosmologists correctly understand how the universe evolved from its early state to its present one. “Planck measures how much dark energy there should be” at present by extrapolating from its state at 380,000 years old, Dodelson said. “We measure how much there is.”

    The DES scientists spent six months processing their data without looking at the results along the way — a safeguard against bias — then “unblinded” the results during a July 7 video conference. After team leaders went through a final checklist, a member of the team ran a computer script to generate the long-awaited plot: DES’s measurement of the fraction of the universe that’s matter (dark and visible combined), displayed together with the older estimate from Planck. “We were all watching his computer screen at the same time; we all saw the answer at the same time. That’s about as dramatic as it gets,” said Gary Bernstein, an astrophysicist at the University of Pennsylvania and co-chair of the DES science committee.

    Planck pegged matter at 33 percent of the cosmos today, plus or minus two or three percentage points. When DES’s plots appeared, applause broke out as the bull’s-eye of the new matter measurement centered on 26 percent, with error bars that were similar to, but barely overlapped with, Planck’s range.

    “We saw they didn’t quite overlap,” Bernstein said. “But everybody was just excited to see that we got an answer, first, that wasn’t insane, and which was an accurate answer compared to before.”

    Statistically speaking, there’s only a slight tension between the two results: Considering their uncertainties, the 26 and 33 percent appraisals are between 1 and 1.5 standard deviations or “sigma” apart, whereas in modern physics you need a five-sigma discrepancy to claim a discovery. The mismatch stands out to the eye, but for now, Frieman and his team consider their galaxy results to be consistent with expectations based on the cosmic microwave background. Whether the hint of a discrepancy strengthens or vanishes as more data accumulate will be worth watching as the DES team embarks on its next analysis, expected to cover its first three years of data.

    If the possible discrepancy between the cosmic-microwave and galaxy measurements turns out to be real, it could create enough of a tension to lead to the downfall of the “Lambda-CDM model” of cosmology, the standard theory of the universe’s evolution. Lambda-CDM is in many ways a simple model that starts with Albert Einstein’s general theory of relativity, then bolts on dark energy and dark matter. A replacement for Lambda-CDM might help researchers uncover the quantum theory of gravity that presumably underlies everything else.

    What Is Dark Energy?

    According to Lambda-CDM, dark energy is the “cosmological constant,” represented by the Greek symbol lambda Λ in Einstein’s theory; it’s the energy that infuses space itself, when you get rid of everything else. This energy has negative pressure, which pushes space away and causes it to expand. New dark energy arises in the newly formed spatial fabric, so that the density of dark energy always remains constant, even as the total amount of it relative to dark matter increases over time, causing the expansion of the universe to speed up.

    The universe’s expansion is indeed accelerating, as two teams of astronomers discovered in 1998 by observing light from distant supernovas. The discovery, which earned the leaders of the two teams the 2011 Nobel Prize in physics, suggested that the cosmological constant has a positive but “mystifyingly tiny” value, Bernstein said. “There’s no good theory that explains why it would be so tiny.” (This is the “cosmological constant problem” that has inspired anthropic reasoning and the dreaded multiverse hypothesis.)

    On the other hand, dark energy could be something else entirely. Frieman, whom colleagues jokingly refer to as a “fallen theorist,” studied alternative models of dark energy before co-founding DES in 2003 in hopes of testing his and other researchers’ ideas. The leading alternative theory envisions dark energy as a field that pervades space, similar to the “inflaton field” that most cosmologists think drove the explosive inflation of the universe during the Big Bang. The slowly diluting energy of the inflaton field would have exerted a negative pressure that expanded space, and Frieman and others have argued that dark energy might be a similar field that is dynamically evolving today.

    DES’s new analysis incrementally improves the measurement of a parameter that distinguishes between these two theories — the cosmological constant on the one hand, and a slowly changing energy field on the other. If dark energy is the cosmological constant, then the ratio of its negative pressure and density has to be fixed at −1. Cosmologists call this ratio w. If dark energy is an evolving field, then its density would change over time relative to its pressure, and w would be different from −1.

    Remarkably, DES’s first-year data, when combined with previous measurements, pegs w’s value at −1, plus or minus roughly 0.04. However, the present level of accuracy still isn’t enough to tell if we’re dealing with a cosmological constant rather than a dynamic field, which could have w within a hair of −1. “That means we need to keep going,” Frieman said.

    The DES scientists will tighten the error bars around w in their next analysis, slated for release next year; they’ll also measure the change in w over time, by probing its value at different cosmic distances. (Light takes time to reach us, so distant galaxies reveal the universe’s past). If dark energy is the cosmological constant, the change in w will be zero. A nonzero measurement would suggest otherwise.

    Larger galaxy surveys might be needed to definitively measure w and the other cosmological parameters. In the early 2020s, the ambitious Large Synoptic Survey Telescope (LSST) will start collecting light from 20 billion galaxies and other cosmological objects, creating a high-resolution map of the universe’s clumpiness that will yield a big jump in accuracy.

    LSST


    LSST Camera, built at SLAC



    LSST telescope, currently under construction 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.

    The data might confirm that we occupy a Lambda-CDM universe, infused with an inexplicably tiny cosmological constant and full of dark matter whose nature remains elusive. But Frieman doesn’t discount the possibility of discovering that dark energy is an evolving quantum field, which would invite a deeper understanding by going beyond Einstein’s theory and tying cosmology to quantum physics.

    “With these surveys — DES and LSST that comes after it — the prospects are quite bright,” Dodelson said. “It is more complicated to analyze these things because the cosmic microwave background is simpler, and that is good for young people in the field because there’s a lot of work to do.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Formerly known as Simons Science News, Quanta Magazine is an editorially independent online publication launched by the Simons Foundation to enhance public understanding of science. Why Quanta? Albert Einstein called photons “quanta of light.” Our goal is to “illuminate science.” At Quanta Magazine, scientific accuracy is every bit as important as telling a good story. All of our articles are meticulously researched, reported, edited, copy-edited and fact-checked.

     
  • richardmitnick 4:50 pm on July 11, 2017 Permalink | Reply
    Tags: 800 million years is the current frontier in reionization studies, , , , , , DES - Dark Energy Survey, Determining when the first galaxies formed is a challenge, LAEs-Lyman alpha emitting galaxies,   

    From phys.org: “Distant galaxies ‘lift the veil’ on the end of the cosmic dark ages” 

    physdotorg
    phys.org

    July 11, 2017

    1
    False color image of a 2 square degree region of the LAGER survey field, created from images taken in the optical at 500 nm (blue), in the near-infrared at 920 nm (red), and in a narrow-band filter centered at 964 nm (green). The last is sensitive to hydrogen Lyman alpha emission at z ~ 7. The small white boxes indicate the positions of the 23 LAEs discovered in the survey. The detailed insets (yellow) show two of the brightest LAEs; they are 0.5 arcminutes on a side, and the white circles are 5 arcseconds in diameter. Credit: Zhen-Ya Zheng (SHAO) & Junxian Wang (USTC).

    Astronomers studying the distant Universe have found that small star-forming galaxies were abundant when the Universe was only 800 million years old, a few percent of its present age. The results suggest that the earliest galaxies, which illuminated and ionized the Universe, formed at even earlier times.

    Long ago, about 300,000 years after the beginning of the Universe (the Big Bang), the Universe was dark. There were as yet no stars and galaxies, and the Universe was filled with neutral hydrogen gas. At some point the first galaxies appeared, and their energetic radiation ionized their surroundings, the intergalactic gas, illuminating and transforming the Universe.

    While this dramatic transformation is known to have occurred sometime in the interval between 300 million years and 1 billion years after the Big Bang, determining when the first galaxies formed is a challenge. The intergalactic gas, which is initially neutral, strongly absorbs and scatters the ultraviolet light emitted by the galaxies, making them difficult to detect.

    To home in on when the transformation occurred, astronomers take an indirect approach. Using the demographics of small star-forming galaxies to determine when the intergalactic gas became ionized, they can infer when the ionizing sources, the first galaxies, formed. If star forming galaxies, which glow in the light of the hydrogen Lyman alpha line, are surrounded by neutral hydrogen gas, the Lyman alpha photons are readily scattered, much like headlights in fog, obscuring the galaxies. When the gas is ionized, the fog lifts, and the galaxies are easier to detect.

    A new study [ApJ] taking this approach has discovered 23 candidate Lyman alpha emitting galaxies (LAEs) that were present 800 million years after the Big Bang (at a redshift of z~7), the largest sample detected to date at that epoch. The study, “Lyman-Alpha Galaxies in the Epoch of Reionization” (LAGER), was carried out by an international team of astronomers from China, the US, and Chile using the Dark Energy Camera (DECam) on the CTIO 4-m Blanco telescope.

    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

    2
    Milestones in the history of the Universe (not to scale). The intergalactic gas was in a neutral state from about 300,000 years after the Big Bang until light from the first generation of stars and galaxies began to ionize it. The gas was completely ionized after 1 billion years. The LAGER study takes a close look at the state of the Universe at 800 million years (yellow box) to investigate when and how this transformation occurred. Credit: NAOJ.

    While the study detected many LAEs, it also found that LAEs were 4 times less common at 800 million years than they were a short time later, at 1 billion years (at a redshift of z~5.7). The results imply that the process of ionizing the Universe began early and was still incomplete at 800 million years, with the intergalactic gas about half neutral and half ionized at that epoch. The low incidence rate of LAEs at 800 million years results from the suppression of their Lyman alpha emission by neutral intergalactic gas.

    The study shows that “the fog was already lifting when the universe was 5% of its current age”, explained Sangeeta Malhotra (Goddard Space Flight Center and Arizona State University), one of the co-leads of the survey.

    Junxian Wang (USTC), the organizer of the study, further explained, “Our finding that the intergalactic gas is 50% ionized at z ~ 7 implies that a large fraction of the first galaxies that ionized and illuminated the universe formed early, less than 800 million years after the Big Bang.”

    For Zhenya Zheng (Shanghai Astronomical Observatory, CAS), the lead author of the paper describing these results, “800 million years is the current frontier in reionization studies.” While hundreds of LAEs have been found at later epochs, only about two dozen candidate LAEs were known at 800 million years prior to the current study. The new results dramatically increase the number of LAEs known at this epoch.

    “None of this science would have been possible without the widefield capabilities of DECam and its community pipeline for data reduction,” remarked coauthor James Rhoads. “These capabilities enable efficient surveys and thereby the discovery of faint galaxies as well as rare, bright ones.”

    To build on these results, the team is “continuing the search for distant star forming galaxies over a larger volume of the Universe”, said Leopoldo Infante (Pontificia Catolica University of Chile and the Carnegie Institution for Science), “to study the clustering of LAEs.” Clustering provides unique insights into how the fog lifts. The team is also investigating the nature of these distant galaxies.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

     
  • richardmitnick 3:38 pm on July 11, 2017 Permalink | Reply
    Tags: , , , , , DES - Dark Energy Survey, Extreme variability quasars, ,   

    From astrobites: “Extreme variability quasars” 

    Astrobites bloc

    Astrobites

    Jul 11, 2017
    Suk Sien Tie

    Title: Extreme variability quasars from the Sloan Digital Sky Survey and the Dark Energy Survey
    Authors: Nick Rumbaugh, Yue Shen, Eric Morganson et al.
    First Author’s Institution: National Center for Supercomputing Applications, IL.
    1
    Status: Submitted to ApJ, open access

    Active galactic nuclei (AGNs), the central active regions of supermassive black holes, have many masks. They span a large range of luminosities from roughly ten billion to ten thousand Milky Ways (even at their dimmest, they are still one of the brightest objects in the Universe). They have varying radio brightnesses and the presence of radio jets is not a luxury to be had by all. When scrutinized with a spectrograph, they reveal telltale signs of different anatomies. Some exhibit broad emission lines, others narrow, and still others both. Therefore, AGNs carry a myriad of different names, such as Seyferts, blazars, and quasars. However, the multifaceted appearances of AGNs are deceiving — the AGN unification theory postulates that which type of AGN you see depends on your viewing angle and the wavelength of light you’re looking in. Otherwise, you’re simply looking at one and the same object, the central bright region of a supermassive black hole.

    All AGNs have one thing in common: they vary in brightness. In (not quite) the (exact) words of Shakespeare, an AGN by any other name would always vary. In particular, quasars (the highest redshift and most luminous subclass of AGN and the main focus of the paper) are known to vary by 10%-30%, corresponding to ~0.1 mag to ~0.3 mag, over the course of many years. The physical mechanism for their variability is still an open question, with the leading theory being temperature fluctuations in the black hole accretion disk driven by an X-ray source near the central black hole. The authors of this paper are not interested in regular varying quasars, instead they are interested in quasars that vary by 1 magnitude or more — the extreme variability quasars.

    There is a hint of such a population from previous studies, such as a joint PanStarrs-SDSS search that uncovered ~40 quasars that vary by more than 1.5 magnitudes.

    U Hawaii Pann-STARRS1 Telescope, located at Haleakala Observatory, Hawaii

    SDSS Telescope at Apache Point Observatory, NM, USA

    Extreme variability quasars are thought to be the larger class of an intriguing group of quasars that has only recently been discovered (oh no, not another group), known as changing look quasars (see this for an example). Changing look quasars pose a significant challenge to the AGN unification model, because they change from one AGN type to another over the course of several decades. More often than not, these changes are accompanied by a large magnitude variation. Aside from studying the properties of the extreme variability quasars, the authors also hope to build a larger sample of changing look quasars in order to probe their origin(s).

    Using both SDSS and the Dark Energy Survey (DES) to construct a search baseline of ~15 years, the authors found ~1000 spectroscopically confirmed quasars that vary by 1 magnitude or more.

    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

    They also recovered all previously known changing look quasars that fall within their footprint. Figure 1 shows the light curves and spectrum for one of their objects. In addition to finding that extreme variability quasars have stronger emission line strengths compared to regular quasars with similar redshifts and luminosities, their Eddington ratios are also lower. The Eddington ratio is a ratio of the quasar luminosity, which depends on the accretion rate, to the Eddington luminosity, which is the theoretical maximum luminosity. Figure 2 shows the relation between the maximum variability of the extreme variability quasars and their Eddington ratios. There is a trend of decreasing Eddington ratios with variability, leading to the interpretation that the extreme variabilities are connected to the Eddington ratios. By extension, the authors attribute the reason changing-look quasars change types to their varying accretion rates caused by internal accretion disk processes.

    2
    An example extreme variability quasar discovered in this study. The top and middle panels show its light curves in two different filter bandpasses at different wavelengths, both of which have dimmed by more than 1 magnitude over ~15 years. The bottom panel shows its SDSS spectrum, which contains the usual broad emission lines associated with quasars. [Figure 2 in paper]

    3
    Fig. 2: Eddington ratio as a function of maximum variability for the extreme variability quasars (red) and regular quasars with similar redshifts and luminosities (black). The blue points are the median Eddington ratio in bins of maximum variability. There is a trend of decreasing Eddington ratio with increasing variability. [Figure 11 in paper]

    Using a simple model, the authors estimated the intrinsic fraction of extreme variability quasars to be between ~30-50%, which is much higher than the observed fraction of 10%. With more frequent searches over a wider area and longer period, we should discover more of these exotic objects to help shed light on the physical mechanism of quasar variability and the phenomena of the quasar population as a whole.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

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

     
  • richardmitnick 11:27 am on June 25, 2017 Permalink | Reply
    Tags: , , , , , D.O.E. Office of Science, DES - Dark Energy Survey, , , Lambda-Cold Dark Matter Accelerated Expansion of the Universe, LBNL/DESI Dark Energy Spectroscopic Instrument,   

    From US D.O.E. Office of Science: “Our Expanding Universe: Delving into Dark Energy” 

    DOE Main

    Department of Energy Office of Science

    06.21.17
    Shannon Brescher Shea
    shannon.shea@science.doe.gov

    Space is expanding ever more rapidly and scientists are researching dark energy to understand why.

    1
    This diagram shows the timeline of the universe, from its beginnings in the Big Bang to today. Image courtesy of NASA/WMAP Science Team.

    The universe is growing a little bigger, a little faster, every day.

    And scientists don’t know why.

    If this continues, almost all other galaxies will be so far away from us that one day, we won’t be able to spot them with even the most sophisticated equipment. In fact, we’ll only be able to spot a few cosmic objects outside of the Milky Way. Fortunately, this won’t happen for billions of years.

    But it’s not supposed to be this way – at least according to theory. Based on the fact that gravity pulls galaxies together, Albert Einstein’s theory predicted that the universe should be expanding more slowly over time. But in 1998, astrophysicists were quite surprised when their observations showed that the universe was expanding ever faster. Astrophysicists call this phenomenon “cosmic acceleration.”

    “Whatever is driving cosmic acceleration is likely to dominate the future evolution of the universe,” said Josh Frieman, a researcher at the Department of Energy’s (DOE) Fermilab [FNAL] and director of the 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

    While astrophysicists know little about it, they often use “dark energy” as shorthand for the cause of this expansion. Based on its effects, they estimate dark energy could make up 70 percent of the combined mass and energy of the universe. Something unknown that both lies outside our current understanding of the laws of physics and is the major influence on the growth of the universe adds up to one of the biggest mysteries in physics. DOE’s Office of Science is supporting a number of projects to investigate dark energy to better understand this phenomenon.

    The Start of the Universe

    Before scientists can understand what is causing the universe to expand now, they need to know what happened in the past. The energy from the Big Bang drove the universe’s early expansion. Since then, gravity and dark energy have engaged in a cosmic tug of war. Gravity pulls galaxies closer together; dark energy pushes them apart. Whether the universe is expanding or contracting depends on which force dominates, gravity or dark energy.

    Just after the Big Bang, the universe was much smaller and composed of an extremely high-energy plasma. This plasma was vastly different from anything today. It was so dense that it trapped all energy, including light. Unlike the current universe, which has expanses of “empty” space dotted by dense galaxies of stars, this plasma was nearly evenly distributed across that ancient universe.

    As the universe expanded and became less dense, it cooled. In a blip in cosmic time, protons and electrons combined to form neutral hydrogen atoms. When that happened, light was able to stream out into the universe to form what is now known as the “cosmic microwave background [CMB].”

    CMB per ESA/Planck


    ESA/Planck

    Today’s instruments that detect the cosmic microwave background provide scientists with a view of that early universe.

    Back then, gravity was the major force that influenced the structure of the universe. It slowed the rate of expansion and made it possible for matter to coalesce. Eventually, the first stars appeared about 400 million years after the Big Bang. Over the next several billion years, larger and larger structures formed: galaxies and galaxy clusters, containing billions to quadrillions (a million billion) of stars. While these cosmic objects formed, the space between galaxies continued to expand, but at an ever slower rate thanks to gravitational attraction.

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

    But somewhere between 3 and 7 billion years after the Big Bang, something happened: instead of the expansion slowing down, it sped up. Dark energy started to have a bigger influence than gravity. The expansion has been accelerating ever since.

    Scientists used three different types of evidence to work out this history of the universe. The original evidence in 1998 came from observations of a specific type of supernova [Type 1a]. Two other types of evidence in the early 2000s provided further support.

    “It was this sudden avalanche of results through cosmology,” said Eric Linder, a Berkeley Lab researcher and Office of Science Cosmic Frontier program manager.

    Now, scientists estimate that galaxies are getting 0.007 percent further away from each other every million years. But they still don’t know why.

    What is Dark Energy?

    “Cosmic acceleration really points to something fundamentally different about how the forces of the universe work,” said Daniel Eisenstein, a Harvard University researcher and former director of the Sloan Digital Sky Survey. “We know of four major forces: gravity, electromagnetism, and the weak and strong forces. And none of those forces can explain cosmic acceleration.”

    So far, the evidence has spurred two competing theories.

    The leading theory is that dark energy is the “cosmological constant,” a concept Albert Einstein created in 1917 to balance his equations to describe a universe in equilibrium. Without this cosmological constant to offset gravity, a finite universe would collapse into itself.

    Today, scientists think the constant may represent the energy of the vacuum of space. Instead of being “empty,” this would mean space is actually exerting pressure on cosmic objects. If this idea is correct, the distribution of dark energy should be the same everywhere.

    All of the observations fit this idea – so far. But there’s a major issue. The theoretical equations and the physical measurements don’t match. When researchers calculate the cosmological constant using standard physics, they end up with a number that is off by a huge amount: 1 X 10^120 (1 with 120 zeroes following it).

    “It’s hard to make a math error that big,” joked Frieman.

    That major difference between observation and theory suggests that astrophysicists do not yet fully understand the origin of the cosmological constant, even if it is the cause of cosmic acceleration.

    The other possibility is that “dark energy” is the wrong label altogether. A competing theory posits that the universe is expanding ever more rapidly because gravity acts differently at very large scales from what Einstein’s theory predicts. While there’s less evidence for this theory than that for the cosmological constant, it’s still a possibility.

    The Biggest Maps of the Universe

    To collect evidence that can prove or disprove these theories, scientists are creating a visual history of the universe’s expansion. These maps will allow astrophysicists to see dark energy’s effects over time. Finding that the structure of the universe changed in a way that’s consistent with the cosmological constant’s influence would provide strong evidence for that theory.

    There are two types of surveys: imaging and spectroscopic. The Dark Energy Survey and Large Synoptic Survey Telescope (LSST) are imaging surveys, while the Baryon Oscillation Spectroscopic Survey (part of the Sloan Digital Sky Survey), eBOSS, and the Dark Energy Spectroscopic Instrument are spectroscopic.


    LSST Camera, built at SLAC



    LSST telescope, currently under construction 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.

    BOSS Supercluster Baryon Oscillation Spectroscopic Survey (BOSS)

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

    Imaging surveys use giant cameras – some the size of cars – to take photos of the night sky. The farther away the object, the longer the light has taken to reach us. Taking pictures of galaxies, galaxy clusters, and supernovae at various distances shows how the distribution of matter has changed over time. The Dark Energy Survey, which started collecting data in 2013, has already photographed more than 300 million galaxies. By the time it finishes in 2018, it will have taken pictures of about one-eighth of the entire night sky. The LSST will further expand what we know. When it starts in 2022, the LSST will use the world’s largest digital camera to take pictures of 20 billion galaxies.

    “That is an amazing number. It could be 10% of all of the galaxies in the observable universe,” said Steve Kahn, a professor of physics at Stanford and LSST project director.

    However, these imaging surveys miss a key data point – how fast the Milky Way and other galaxies are moving away from each other. But spectroscopic surveys that capture light outside the visual spectrum can provide that information. They can also more accurately estimate how far away galaxies are. Put together, this information allows astrophysicists to look back in time.

    The Baryon Oscillation Spectroscopic Survey (BOSS), part of the larger Sloan Digital Sky Survey, was one of the biggest projects to take, as the name implies, a spectroscopic approach. It mapped more than 1.2 million galaxies and quasars.

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

    However, there’s a major gap in BOSS’s data. It could measure what was going on 5 billion years ago using bright galaxies and 10 billion years ago using bright quasars. But it had nothing about what was going on in-between. Unfortunately, this time period is most likely when dark energy started dominating.

    “Seven billion years ago, dark energy starts to really dominate and push the universe apart more rapidly. So we’re making these maps now that span that whole distance. We start in the backyard of the Milky Way, our own galaxy, and we go out to 7 billion light years,” said David Schlegel, a Berkeley Lab researcher who is the BOSS principal investigator. That 7 billion light years spans the time from when the light was originally emitted to it reaching our telescopes today.

    Two new projects are filling that gap: the eBOSS survey and the Dark Energy Spectroscopic Instrument (DESI). eBOSS will target the missing time span from 5 to 7 billion years ago.

    4
    SDSS eBOSS.

    DESI will go back even further – 11 billion light years. Even though the dark energy was weaker then relative to gravity, surveying a larger volume of space will allow scientists to make even more precise measurements. DESI will also collect 10 times more data than BOSS. When it starts taking observations in 2019, it will measure light from 35 million galaxies and quasars.

    “We now realize that the majority of … the universe is stuff that we’ll never be able to directly measure using experiments here on Earth. We have to infer their properties by looking to the cosmos,” said Rachel Bean, a researcher at Cornell University who is the spokesperson for the LSST Dark Energy Science Collaboration. Solving the mystery of the galaxies rushing away from each other, “really does present a formidable challenge in physics. We have a lot of work to do.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    The mission of the Energy Department is to ensure America’s security and prosperity by addressing its energy, environmental and nuclear challenges through transformative science and technology solutions.

    Science Programs Organization

    The Office of Science manages its research portfolio through six program offices:

    Advanced Scientific Computing Research
    Basic Energy Sciences
    Biological and Environmental Research
    Fusion Energy Sciences
    High Energy Physics
    Nuclear Physics

    The Science Programs organization also includes the following offices:

    The Department of Energy’s Small Business Innovation Research and Small Business Technology Transfer Programs, which the Office of Science manages for the Department;
    The Workforce Development for Teachers and Students program sponsors programs helping develop the next generation of scientists and engineers to support the DOE mission, administer programs, and conduct research; and
    The Office of Project Assessment provides independent advice to the SC leadership regarding those activities essential to constructing and operating major research facilities.

     
  • richardmitnick 4:27 pm on May 21, 2017 Permalink | Reply
    Tags: , , , , , , DeeDee, DES - Dark Energy Survey   

    From Astro Watch: “The Mysteries of DeeDee: One of the Solar System’s Most Distant Object Studied by Astronomers” 

    Astro Watch bloc

    Astro Watch

    May 21, 2017
    No writer credit found

    1
    Artist concept of the planetary body 2014 UZ224, more informally known as DeeDee. ALMA was able to observe the faint millimeter-wavelength “glow” emitted by the object, confirming it is roughly 635 kilometers across. At this size, DeeDee should have enough mass to be spherical, the criteria necessary for astronomers to consider it a dwarf planet, though it has yet to receive that official designation.
    Credit: Alexandra Angelich (NRAO/AUI/NSF)

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres

    Lurking somewhere beyond Neptune, the planetary body 2014 UZ224, nicknamed DeeDee, is one of the most distant objects in the solar system. Although DeeDee was lately studied by astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, this faraway dim object still holds many mysteries waiting to be uncovered.

    2014 UZ224 is a 635-kilometer-wide trans-Neptunian object (TNO), orbiting the sun every 1,136 years. The object was detected by a team of astronomers led by David Gerdes of the University of Michigan, using the 4-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in Chile as part of ongoing observations for the 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

    They announced their discovery in October 2016 and informally dubbed the newly found TNO DeeDee, which is short for Distant Dwarf.

    Recent observations of DeeDee conducted with ALMA allowed Gerdes and his team to reveal the object’s fundamental orbital parameters as well as its size and albedo. Based on the new findings, the researchers assume that 2014 UZ224 is most likely a dwarf planet with a mixed ice-rock composition. However, more observations are needed in order to draw final conclusions about the real nature of this distant TNO.

    “We expect to make further optical observations of DeeDee with the Blanco 4-meter telescope during the Dark Energy Survey’s upcoming observing season, from August 2017 to February 2018. These observations will help refine DeeDee’s orbital parameters,” Gerdes told Astrowatch.net.

    DeeDee’s orbital and physical properties could reveal important insights about the formation of planets, including Earth. Such objects are leftovers from the formation of the solar system, thus could be real treasure troves of information regarding the history and evolution of celestial bodies.

    DeeDee is currently about 92 astronomical units (AU) away from the sun. This is roughly three times Pluto’s current distance. The object will reach it’s perihelion distance of about 38 AU in the year 2142, when due to its proximity it could be studied by a dedicated probe. Hence, the only opportunity now available to study this TNO is to employ ground-based telescopes or space observatories flying in Earth’s orbit.

    “A dedicated mission to study this object from close range is not feasible at this time. DeeDee will reach its perihelion distance of 38 AU in the year 2142. Perhaps at that point in the distant future a dedicated mission will be both practical and scientifically interesting,” Gerdes noted.

    TNOs are icy bodies in orbit beyond Neptune. Observations of these objects could provide better understanding of accretion and evolution processes that governed planetary formation in our solar system as well as in other dusty star discs. Currently, NASA’s New Horizons spacecraft, after completing its flyby of Pluto, is on its way to study such celestial body designated 2014 MU69.

    NASA/New Horizons spacecraft

    This object is about 44 AU away from the sun. New Horizons is expected to arrive there in January 2019.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: