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  • richardmitnick 6:22 pm on February 8, 2016 Permalink | Reply
    Tags: , , Dark Energy Survey   

    From DES: “Dark Energy Camera Legacy Survey Announces Second Data Release” 

    Dark Energy Icon

    The Dark Energy Survey

    The Dark Energy Camera Legacy Survey (DECaLS) announced its second data release (DR2) on 15 January 2016. DECaLS (PIs: David Schlegel and Arjun Dey) is in the middle of mapping 6200 square degrees of the extragalactic sky in g, r and z using the Dark Energy Camera on the Blanco 4-m telescope at the Cerro Tololo Inter-American Observatory. The project is designed to investigate a broad range of astrophysical questions, ranging from studies of Milky Way structure and galaxy evolution to large-scale structure and cosmology. The survey goals and the first data release were described in an earlier issue of Currents.

    DECaLS DR2 includes reduced images and source catalogs covering approximately 2100 square degrees of sky in g- and r-band and 5300 square degrees in z-band. Roughly 1800 square degrees has been imaged in all three bands. The area covered can be visualized using the project’s Imagine Sky Viewer built by Dr. Dustin Lang. An Image Gallery of Large Galaxies constructed by Dr. John Moustakas is also available.

    DR2 includes not only all the data taken by DECaLS from August 2014 through June 2015, but also all public DECam g-, r-, and z-band data within the DECaLS footprint obtained by other projects. The latter include data (now public) from the Dark Energy Survey in the “Stripe 82” region.

    Mapping the Sky. DECaLS is one of three surveys that will jointly image 14,000 square degrees—nearly one-third of the sky—to provide targets for the Dark Energy Spectroscopic Instrument cosmology project. The other two projects are the Mayall z-band Legacy Survey (MzLS), which begins in February 2016, and the Beijing-Arizona Sky Survey (BASS), which is underway at the Bok Telescope on Kitt Peak. MzLS and BASS will provide g- ,r-, and z- band imaging at declinations north of +34 degrees.

    Making it Public. All three surveys are being run as public projects, with no proprietary period for the raw data. Reduced images are available as soon as the pipeline processing at NOAO is complete, and official data releases are scheduled every 6 months. All of the data will be served by the NOAO Science Archive and the National Energy Research Scientific Computing Center at the Lawrence Berkeley National Laboratory. For further details, please see legacysurvey.org.

    See the full article here .

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    Dark Energy Camera
    DECam, built at FNAL

    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO Victor M Blanco Telescope at Cerro Tololo which houses the DECAm

    The Dark Energy Survey (DES) is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. This collaboration [has built] an extremely sensitive 570-Megapixel digital camera, DECam, and [has mounted] it on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory high in the Chilean Andes. Started in Sept. 2012 and continuing for five years, DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.

     
  • richardmitnick 2:25 pm on February 5, 2016 Permalink | Reply
    Tags: , , Dark Energy Survey, David Parkinson Interview   

    From DES: “DEScientist of the Week: David Parkinson” 

    Dark Energy Survey

    The Dark Energy Survey

    February 5, 2016
    No writer credit found

    Meet David Parkinson, Postdoc at the University of Queensland!

    DES David Parkinson
    David Parkinson

    At the University of Sussex, David was part of the DES supernova project, looking at predicted constraints on the dark energy from using supernovae as standard candles. Now at the University of Queensland, he is part of the OzDES survey, making follow-up observations of DES galaxies using the AAOmega spectrograph on the 3.9m Anglo-Australian Telescope.

    ANU AAOmega spectrograph Anglo Australian Telescope
    AAO AAOmega spectrograph on the Anglo-Australian Telescope

    Anglo Australian Telescope Exterior
    Anglo Australian Telescope Interior
    AAO Anglo-Australian Telescope

    We asked David a few more questions — here’s what he had to say:

    What is your favorite part about being a scientist?

    My favorite part of being a scientist is thinking about the big questions of why the Universe is the way it is. Why do we think our theory of gravity is the correct one? Why does the Universe have only three spatial dimensions, not two or forty-seven? And I enjoy the process of finding things out, of using my mind to learn something new, based on logic and mathematics.

    When did you know you wanted to be a scientist?

    I grew up learning about space travel and astronomy from my Dad, who worked as a rocket engineer. But I didn’t actually want to be a scientist growing up. Originally I wanted to be an archaeologist! But learning about modern physics (cosmology, quantum mechanics) as a teenager I changed my mind, and went into astrophysics instead.

    Do you have any hobbies or play any sports?

    I play a lot of board games. One of my favourites is “Ticket to Ride” (where the aim is to build as many train lines as possible), which me and my wife play a lot. Board games have come a long way, and are a lot more fun than the fairly dull games I remember from my childhood.

    If you weren’t a scientist, what would your dream job be?

    I can’t really imagine not being a scientist, but if I wasn’t I would like to be a writer. Fiction or non-fiction, books or screenplays, it doesn’t matter – it would be great to be a professional writer.

    Any other fun facts we should know?

    I was observing at the Anglo-Australian Telescope during the bush fires that threatened Siding Spring Observatory in January 2013 [http://www.space.com/19254-australi…. ].

    Siding Spring Campus
    Siding Spring Observatory

    They actually had to evacuate us from the site! It is scary to be told “The mountain you are standing on is on fire. Please leave as quickly as you can.”

    Any advice for aspiring scientists?

    Science is a hard field to work in, and requires a high degree of dedication. If you’re very interested in science, but happy just to read about it in the newspaper, maybe think about a different career. But if you need to find things out for yourself, then science can be an incredibly rewarding and satisfying career path.

    See the full article here .

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    Dark Energy Camera

    The Dark Energy Survey (DES) is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. This collaboration [has built] an extremely sensitive 570-Megapixel digital camera, DECam, and [has mounted] it on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory high in the Chilean Andes. Started in Sept. 2012 and continuing for five years, DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.

     
  • richardmitnick 10:44 am on January 19, 2016 Permalink | Reply
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    From FNAL: “Dark Energy Survey releases early data” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    Dark Energy Icon

    January 19, 2016
    Andre Salles

    Dark Energy Camera
    CTIO Victor M Blanco 4m Telescope
    DECam, the Dark Energy camera, built at FNAL, and the CTIO/Victor M Blanco 4 meter telescope in Chile in which it is housed.

    The Dark Energy Survey is now in its third year of capturing eye-popping images of the cosmos with its primary instrument, the Dark Energy Camera. Before the survey proper began in August 2013, however, scientists spent months testing the camera, putting it through its paces.

    Now, catalogs of galaxies and stars derived from the data collected during that Science Verification season (November 2012 to February 2013) have been released to the public. Astronomers and astronomy buffs can download the data from the website for the National Center for Supercomputing Applications at the University of Illinois, which manages the processing of all the images taken for the Dark Energy Survey.

    This is good news for the astronomy community, as the catalogs released last week contain measurements of more than 25 million objects. Scientists on the Dark Energy Survey have used this data to, among other things, create the largest-yet dark matter mass map. The Science Verification data covers only 3 percent of the survey area (itself roughly one-eighth of the sky), so there is much more to come.

    The Dark Energy Survey is a five-year effort to map that survey area in unprecedented detail. Scientists will use the data collected to probe the phenomenon of dark energy, the mysterious force that makes up about three-quarters of the universe. The Dark Energy Camera was built and tested at Fermilab and is mounted on the Blanco telescope at the National Optical Astronomy Observatory’s Cerro Tololo Inter-American Observatory in Chile.

    The Dark Energy Survey is a collaboration of more than 300 scientists from 25 institutions in six countries. Funding for DES projects is provided by the U.S. Department of Energy Office of Science, the National Science Foundation, and other funding agencies.

    See the full article here .

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    Fermilab Campus

    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.

     
  • richardmitnick 8:41 am on January 16, 2016 Permalink | Reply
    Tags: A New Method to Measure Galaxy Bias, , , Dark Energy Survey   

    From DES: “A New Method to Measure Galaxy Bias by Combining the Density and Weak Lensing Fields” 

    Dark Energy Icon
    The Dark Energy Survey

    January 15, 2016
    A New Method to Measure Galaxy Bias by Combining the Density and Weak Lensing Fields (http://arxiv.org/abs/1601.00160)
    Galaxy Bias From the DES Science Verification Data: Combining Galaxy Density Maps and Weak Lensing Maps (http://arxiv.org/abs/1601.00405)

    We can study the large scale structures of matter that form in the Universe from the distribution of the galaxies that we observe with telescopes. However, most of the matter in the Universe is made of dark matter, which does not interact with light, and hence it cannot be directly observed. Because of this, it is very important to understand the relation between the dark matter distribution and the galaxy distribution. The densest areas of dark matter will pull together visible matter, like stars and gas, eventually forming galaxies. Conversely, areas with less dark matter may not host galaxies.

    In these papers, we develop and apply a method to make a direct measurement of galaxy bias, a parameter that quantifies the relation between the dark matter and galaxy densities in the Universe. With a very good knowledge of galaxy bias, we would be able to infer the dark matter distribution form the distribution of galaxies with a very high precision.

    Our method uses measurements of gravitational lensing. According to [Albert] Einstein’s theory of [general relativity], when light travels from a source, its trajectory is distorted due to the presence of mass around the trajectory. When the light traveling to us from distant ‘background’ galaxies gets distorted in this way, the shapes of the galaxies appear to change very slightly, but in a recognizable pattern. This effect is called weak gravitational lensing. By studying weak lensing, we can measure the projected total mass between us and the ‘background’ galaxies and generate maps of this mass distribution (which is mostly dark matter).

    It’s important to note note that the ‘background’ galaxies are different than the galaxies [of which] we are measuring the distribution . As seen in the example figure below, the galaxies [of which] we measure the distribution (shaded in yellow) are closer, and we measure how they differ in their distribution compared to dark matter. The ‘background’ galaxies are further away, and their only use in this paper is to see how their shapes are distorted, which tells us there is closer dark matter causing gravitational lensing.

    Temp 1
    Image credit: https://upload.wikimedia.org/wikipedia/commons/b/b9/Gravitational-lensing-3d.png

    We study the relation between the galaxy distribution and the dark matter distribution (the galaxy bias) by comparing the distribution of mass inferred from weak lensing with the distribution of the galaxies in the same region. In particular, we calculate the weak lensing effect that we would detect if the distribution of galaxies and matter were the same. Then, we compare this calculated weak lensing field with the real one, that we obtain from the distortions in the shape of the ‘background’ galaxies. We obtain the galaxy bias parameter from comparing the calculated and the real weak lensing fields, which represent the galaxy and matter distributions respectively.

    Key to our analysis was the use of simulations. Simulations are fake data that we use to test analysis techniques in a controlled way. The properties of these simulated universes are calculated according to the laws of [general relativity] and include the effects of dark matter and dark energy close to what we observe in the real Universe. In the simulation, we produce galaxy catalogues and weak lensing effects that can be used to test our analysis techniques. Since we know the “true” galaxy bias in our simulations, we can examine how different measurement errors can cause our measurements to deviate from the true answer. Potential errors due to the area of the sky we use, and the uncertainty of the distance to the ‘background’ galaxies are especially important effects we check for in the simulations.

    Temp 2

    Above is a plot of our weak lensing maps from DES science verification data. Red indicates a higher density of matter in that direction. Blue indicates an area under-dense in matter.

    The figure below shows our measurement of how galaxy bias changes with redshift (or equivalently, how it changes through the history of the Universe), and compares our results with other studies from DES science verification data. The differences may be due to errors, or intrinsic differences of how the galaxy bias is measured by these different techniques. More data from DES should give us greater insight on galaxy bias from multiple techniques.

    Temp 3
    Chang+ 2016, Figure 6

    We find that our results are comparable with other studies of galaxy bias in this DES dataset, with some differences. Based on studies with simulations, we find that our technique’s accuracy improves greatly with area of the survey. Given that science verification data is only 3% of the full DES area (150 out of 5000 square degrees), the full benefits of our technique can be applied with future DES data.
    Galaxy bias is an unknown quantity that affects many attempts to understand cosmology from direct observations of the distribution and evolution of galaxies. Measurements of galaxy bias will allow us to infer the dark matter distribution and study the evolution of structure in the Universe more precisely, which is crucial for understanding the nature of dark energy.

    About the DArchive Authors:

    5
    Arnau Pujol graduated in Physics in Barcelona (Universitat Autònoma de Barcelona). After obtaining a Masters in high energy physics, astrophysics and cosmology, he started to work in the Institut de Ciències de l’Espai (ICE) from Barcelona as a PhD student. He is currently finishing his PhD thesis, where he has been focused on the study of galaxy clustering and bias.

    6
    After finishing undergraduate in Taiwan (National Taiwan University), Chihway Chang graduated from Stanford University as a PhD, where she worked on LSST image simulations and weak gravitational lensing. She then moved to the beautiful country of Switzerland as a postdoc at ETH Zurich, where she joined DES and began exploring the exciting dataset from DES. She works mainly in weak lensing, generating mass maps and experimenting on different ways of using them together with other cosmological probes.

    See the full article here .

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    Dark Energy Camera

    The Dark Energy Survey (DES) is designed to probe the origin of the accelerating universe and help uncover the nature of dark energy by measuring the 14-billion-year history of cosmic expansion with high precision. More than 120 scientists from 23 institutions in the United States, Spain, the United Kingdom, Brazil, and Germany are working on the project. This collaboration [has built] an extremely sensitive 570-Megapixel digital camera, DECam, and [has mounted] it on the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory high in the Chilean Andes. Started in Sept. 2012 and continuing for five years, DES will survey a large swath of the southern sky out to vast distances in order to provide new clues to this most fundamental of questions.

     
  • richardmitnick 5:36 pm on December 14, 2015 Permalink | Reply
    Tags: , , , Dark Energy Survey, ,   

    From FNAL: “Gravitational wave hunters team with astrophysicists” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    December 14, 2015
    Chris Patrick

    The Dark Energy Camera [DECam], built to map the southern sky, sits inside a telescope in Chile.

    Fermilab DECam
    DECam, built at FNAL

    As its name suggests, it helps scientists to look for the origin of dark energy, the mysterious force that pushes the universe apart.

    Now the camera has another job: It’s acting as eyes in the hunt for sources of gravitational waves.

    A massive object, such as a star or a black hole, distorts the fabric of space — sort of the way a bowling ball bends the surface of a trampoline. If the object is accelerating, this distortion pulses outward in ripples traveling at the speed of light. These ripples are gravitational waves. But nobody has been able to record them so far.

    “Gravitational waves are sort of the last prediction of [Albert] Einstein’s that has yet to be experimentally verified,” said Rick Kessler, senior research associate at the University of Chicago.

    Theory predicts that even puny humans make gravitational waves. But because our mass and accelerations are small, they’re too weak to notice. Most gravitational waves are. That’s why scientists haven’t directly detected them yet, although Albert Einstein predicted their existence 100 years ago.

    There is indirect evidence that gravitational waves exist. It comes from a particular system of two neutron stars orbiting each other about 20,000 light-years away from Earth. Scientists have monitored the dizzying dance of these compact stars, together known as the Hulse-Taylor system, for more than 40 years.

    Einstein predicted that gravitational waves carry energy away from a system. Removing energy from two orbiting objects shrinks their paths as if they were being lassoed together. The objects get closer and closer until, eventually, they merge in a cataclysmic collision.

    Watching the stars in the Hulse-Taylor system gradually fall toward each other gives scientists indirect evidence that Einstein was right (again) — these neutron stars are losing energy in the form of gravitational waves, exactly as predicted.

    “But we’re experimentalists,” Kessler said. “We want direct evidence.”

    That’s where the Laser Interferometer Gravitational-wave Observatory comes in.

    Caltech Ligo
    Advanced LIGO

    Scientists built LIGO in an attempt to detect gravitational waves for the first time. And to find out more about the sources of potential gravitational waves, LIGO scientists are now coordinating their measurements with observations made by the Dark Energy Camera on the Blanco Telescope [pictured below].

    1
    DES-GW is using the Dark Energy Camera in the Blanco Telescope in Chile to look for sources of gravitational waves. The red, orange and yellow areas the inset represent gravitational waves, and the bright light represents the source of these waves. The thin white arc illustrates a narrow area of sky where LIGO scientists believe a gravitational wave may have originated.

    LIGO, funded by the National Science Foundation and other public and private institutions, has two detectors. One resides in Louisiana, the other in the state of Washington. They’re L-shaped, each outfitted with two perpendicular arms 2.5 miles long. Lasers shoot through the arms and bounce off mirrors that send them back to their source to combine and form what are known as interference patterns. Observing changes to these interference patterns due changes in space-time is key to directly detecting gravitational waves. That’s because gravitational waves ever so slightly squeeze and then stretch space, drawing separated points of matter a smidge closer together and then a smidge further apart.

    The strongest space-time ripples are produced by violent cosmic events like the merging of two neutron stars (which will happen to the Hulse-Taylor system in 300 million years) or the collision of two black holes. Although these waves are actually quite feeble by the time they travel a few hundred million light-years to Earth, they will almost imperceptibly squeeze and stretch LIGO’s detector arms.

    This faint manipulation will temporarily shorten or lengthen the detectors’ arms by 1,000 times less than the size of a proton. Changing the arm length alters the distance the lasers travel, which will show up as a slight shift in their interference pattern. Scientists can then read the interference pattern like a gravitational wave’s fingerprint, giving them direct evidence that space-time ripples exist.

    “The detectors will tell us that a gravitational wave came from somewhere in a banana-shaped band of sky,” said Daniel Holz, associate professor at the University of Chicago who is on the LIGO experiment. “The problem is that the band is very large. It’s on the order of 400 times the size of the full moon.”

    Although LIGO can point scientists in the general direction from which gravitational wave came, it can’t pick out the exact location of the source.

    “That’s why they need the eyes of the Dark Energy Camera to go look in that general direction,” said Marcelle Soares-Santos, associate scientist at the U.S. Department of Energy’s Fermilab.

    Members of the Dark Energy Survey, including Soares-Santos and other Fermilab scientists, have partnered with LIGO in the hunt for gravitational waves. They’re calling themselves the DES-GW group. Holz, who is also a member of DES-GW, said the team is a mixture of both gravitational wave and dark energy survey experts.

    DES-GW will use the Dark Energy Camera to help LIGO search for the source of the gravitational waves it detects. Unlike most telescopes, the Dark Energy Camera is just the right size and has the right sensitivity to act as LIGO’s eyes. It can cover the banana-shaped area of the sky that LIGO looks at in 20 to 30 images.

    When LIGO thinks it’s detected a gravitational wave, it will alert DES-GW collaborators, who will alert the Dark Energy Camera operators. LIGO and DES-GW have already joined forces and begun working together during the current season.

    “With the Dark Energy Camera we’re trying to find an optical signature that accompanies the gravitational waves,” said Kessler, who is also a member of DES-GW.

    “This is the frontier of science — we don’t really know what we’ll see,” Holz said. “But there’s an expectation that some systems will emit light at the same time as gravitational waves.”

    Using the Dark Energy Camera to see this light, the optical signature of the gravitational waves’ source, could tell scientists more about the systems that produce them. This system may be made up of two neutron stars, two black holes or a neutron-black hole pair. And it would make history.

    “We would be the first ones to directly detect gravitational waves and see light from the same event,” Soares-Santos said.

    Soares-Santos is most excited about the potential of using this light as a tool to reconstruct the history of expansion of the universe, the same way supernovae are used today.

    “There are lots of ifs and maybes,” Soares-Santos said of this possibility. “But at the same time, it’s exciting.”

    Holz finds the most thrill in the prospect of surprise.

    “Since we’ve never measured the universe in this way before, we just don’t know what’s out there,” Holz said. “That’s the real excitement.”

    See the full article here .

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    Fermilab Campus

    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.

     
  • richardmitnick 6:00 pm on November 23, 2015 Permalink | Reply
    Tags: , , Dark Energy Survey,   

    From phys.org: “Scientists detect stellar streams around Magellanic Clouds” 

    physdotorg
    phys.org

    November 23, 2015
    Tomasz Nowakowski

    1
    Seen from the southern skies, the Large and Small Magellanic Clouds (the LMC and SMC, respectively) are bright patches in the sky. Image credit: ESO/S. Brunier

    Astronomers from the University of Cambridge, U.K., have detected a number of narrow streams and diffuse debris clouds around two nearby irregular dwarf galaxies called the Magellanic Clouds. The research also implies that one of these dwarf galaxies – the Large Magellanic Cloud (LMC) could be more massive than previously thought. A paper detailing these findings was published last week on ArXiv.

    “Even though a prominent gaseous stream emanating from the clouds has been known and studied for some time, no obvious stellar streams had been found until recently,” Vasily Belokurov, one of the co-authors of the paper, told Phys.org.

    Belokurov, together with his colleague Sergey Koposov, used the Dark Energy Survey (DES) to track down stellar debris on the outskirts of the Magellanic Clouds.

    Dark Energy Survey
    Dark Energy CameraCTIO Victor M Blanco 4m Telescope
    Dark Energy Camera and the Blanco telescope in Chile where it is housed.

    They were searching for the Magellanic stellar halo substructure using blue horizontal-branch (BHB) stars as tracers. BHBs are old and metal-poor stars powered by helium fusion that appear blue. They were chosen by Cambridge scientists as these stars suffer little contamination from other stellar populations. BHBs can be easily picked up and are one of the best stellar standard rulers available.

    “Thanks to their unique properties, BHBs have proven to be a powerful tool to scrutinize the galactic halo out from the core to its far-flung fringes,” the researchers wrote in the paper.

    “In the halo, not only can these old and metal-poor stars be easily identified above the foreground of other populations thanks to their peculiar color, they are also one of the best stellar distance estimators available,” they added.

    DES is an astronomical survey specifically designed to measure the expansion history of the universe. It has one of the widest fields of view available for ground-based optical and infrared imaging. The scientists used DES’ Year 1 public dataset for this study.

    “To study the stellar halo substructure around the Magellanic Clouds, we use the photometric catalogs obtained from the publicly released DES Year 1 imaging, in particular, the latest improved version of the reduction,” the paper reads.

    Scanning many BHBs, the astronomers detected the stellar halo of the Magellanic system and its substructures. Each of these substructures is different in shape, extent and luminosity, and deserves its own detailed analysis.

    The discovery of these stellar halo substructures led the scientists to ponder on the possible revision of our current knowledge about LMC’s mass. They ask whether the LMC could, in fact, be much more massive than has been previously assumed.

    “Our discoveries imply that the Large Magellanic Cloud might have been a lot more massive than we previously thought. To figure out exactly how much more massive, we need to follow these streams up with spectroscopy in order to measure their velocities,” Belokurov said.

    The researchers also noted that a combination of the deep imaging and spectroscopic follow-up of the tidal debris could provide more information about the orbital history of the Magellanic Clouds. This could be crucial to our understanding of the Clouds’ future as they are in the process of merging with our Milky Way galaxy. They are currently on their way to join the already crowded Milky Way halo.

    More information: Stellar streams around the Magellanic Clouds, arXiv:1511.03667 [astro-ph.GA], arxiv.org/abs/1511.03667

    See the full article here .

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    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 11:45 am on August 17, 2015 Permalink | Reply
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    From FNAL: “Dark Energy Survey finds more celestial neighbors” 

    FNAL II photo

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    New dwarf galaxy candidates could mean our sky is more crowded than we thought.

    Temp 1

    Media contact:

    Andre Salles, Fermilab Office of Communication, media@fnal.gov, 630-840-3351

    Science contacts:

    Josh Frieman, Fermilab, director of the Dark Energy Survey, frieman@fnal.gov, 847-274-0429
    Alex Drlica-Wagner, David N. Schramm fellow, Fermilab, kadrlica@fnal.gov
    Keith Bechtol, John Bahcall fellow, University of Wisconsin-Madison, keith.bechtol@icecube.wisc.edu
    Risa Wechsler, SLAC/Stanford University, risa@slac.stanford.edu
    Basilio Santiago, Federal University of Rio Grande do Sul, basilio.santiago@ufrgs.br

    Scientists on the Dark Energy Survey, using one of the world’s most powerful digital cameras, have discovered eight more faint celestial objects hovering near our Milky Way galaxy. Signs indicate that they, like the objects found by the same team earlier this year, are likely dwarf satellite galaxies, the smallest and closest known form of galaxies.

    Dark Energy Survey
    Dark Energy Camera
    Dark Energy Camera

    Satellite galaxies are small celestial objects that orbit larger galaxies, such as our own Milky Way. Dwarf galaxies can be found with fewer than 1,000 stars, in contrast to the Milky Way, an average-size galaxy containing billions of stars. Scientists have predicted that larger galaxies are built from smaller galaxies, which are thought to be especially rich in dark matter, the substance that makes up about 25 percent of the total matter and energy in the universe. Dwarf satellite galaxies, therefore, are considered key to understanding dark matter and the process by which larger galaxies form.

    The main goal of the Dark Energy Survey (DES), as its name suggests, is to better understand the nature of dark energy, the mysterious stuff that makes up about 70 percent of the matter and energy in the universe. Scientists believe that dark energy is the key to understanding why the expansion of the universe is speeding up. To carry out its dark energy mission, DES takes snapshots of hundreds of millions of distant galaxies. However, some of the DES images also contain stars in dwarf galaxies much closer to the Milky Way. The same data can therefore be used to probe both dark energy, which scientists think is driving galaxies apart, and dark matter, which is thought to hold galaxies together.

    Scientists can only see the faintest dwarf galaxies when they are nearby, and had previously only found a few of them. If these new discoveries are representative of the entire sky, there could be many more galaxies hiding in our cosmic neighborhood.

    “Just this year, more than 20 of these dwarf satellite galaxy candidates have been spotted, with 17 of those found in Dark Energy Survey data,” said Alex Drlica-Wagner of the U.S. Department of Energy’s (DOE) Fermi National Accelerator Laboratory, one of the leaders of the DES analysis. “We’ve nearly doubled the number of these objects we know about in just one year, which is remarkable.”

    In March, researchers with the Dark Energy Survey and an independent team from the University of Cambridge jointly announced the discovery of nine of these objects in snapshots taken by the Dark Energy Camera, the extraordinary instrument at the heart of the DES, an experiment funded by the DOE, the National Science Foundation and other funding agencies. Two of those have been confirmed as dwarf satellite galaxies so far.

    Prior to 2015, scientists had located only about two dozen such galaxies around the Milky Way.

    “DES is finding galaxies so faint that they would have been very difficult to recognize in previous surveys,” said Keith Bechtol of the University of Wisconsin-Madison. “The discovery of so many new galaxy candidates in one-eighth of the sky could mean there are more to find around the Milky Way.”

    The closest of these newly discovered objects is about 80,000 light-years away, and the furthest roughly 700,000 light-years away. These objects are, on average, around a billion times dimmer than the Milky Way and a million times less massive. The faintest of the new dwarf galaxy candidates has about 500 stars.

    Most of the newly discovered objects are in the southern half of the DES survey area, in close proximity to the Large Magellanic Cloud and the Small Magellanic Cloud. These are the two largest satellite galaxies associated with the Milky Way, about 158,000 light-years and 208,000 light-years away, respectively. It is possible that many of these new objects could be satellite galaxies of these larger satellite galaxies, which would be a discovery by itself.

    “That result would be fascinating,” said Risa Wechsler of DOE’s SLAC National Accelerator Laboratory. “Satellites of satellites are predicted by our models of dark matter. Either we are seeing these types of systems for the first time, or there is something we don’t understand about how these satellite galaxies are distributed in the sky.”

    Since dwarf galaxies are thought to be made mostly of dark matter, with very few stars, they are excellent targets to explore the properties of dark matter. Further analysis will confirm whether these new objects are indeed dwarf satellite galaxies and whether signs of dark matter can be detected from them.

    The 17 dwarf satellite galaxy candidates were discovered in the first two years of data collected by the Dark Energy Survey, a five-year effort to photograph a portion of the southern sky in unprecedented detail. Scientists have now had a first look at most of the survey area, but data from the next three years of the survey will likely allow them to find objects that are even fainter, more diffuse or farther away. The third survey season has just begun.

    “This exciting discovery is the product of a strong collaborative effort from the entire DES team,” said Basilio Santiago, a DES Milky Way Science Working Group coordinator and a member of the DES-Brazil Consortium. “We’ve only just begun our probe of the cosmos, and we’re looking forward to more exciting discoveries in the coming years.”

    View the Dark Energy Survey analysis online. Follow the Dark Energy Survey on Facebook and Twitter. For images taken with the Dark Energy Camera, visit the experiment’s photo blog, Dark Energy Detectives.

    The Dark Energy Survey is a collaboration of more than 300 scientists from 25 institutions in six countries. Its primary instrument, the 570-megapixel Dark Energy Camera, is mounted on the 4-meter Blanco telescope at the National Optical Astronomy Observatory’s Cerro Tololo Inter-American Observatory in Chile, and its data is processed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign.

    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    Victor M. Banco 4m telescope

    Funding for the DES Projects has been provided by the U.S. Department of Energy Office of Science, the U.S. National Science Foundation, the Ministry of Science and Education of Spain, the Science and Technology Facilities Council of the United Kingdom, the Higher Education Funding Council for England, ETH Zurich for Switzerland, the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, the Kavli Institute of Cosmological Physics at the University of Chicago, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and the Ministério da Ciência e Tecnologia, the Deutsche Forschungsgemeinschaft and the collaborating institutions in the Dark Energy Survey, which can be found at http://www.darkenergysurvey.org/collaboration.

    The DOE Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Fermilab Campus

    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.

     
  • richardmitnick 10:55 am on July 24, 2015 Permalink | Reply
    Tags: , , Dark Energy Survey,   

    From FNAL “Frontier Science Result: DES Cosmic shear cosmology with the Dark Energy Survey” 

    FNAL Home

    Fermilab is an enduring source of strength for the US contribution to scientific research world wide.

    July 24, 2015
    Matthew R. Becker, Stanford University, and Joe Zuntz, University of Manchester for the Dark Energy Survey

    Temp 1
    The constraints we deduce from DES SV lensing data (in purple) on the amount of matter in the universe, Ωm, and the amplitude of fluctuations in that matter, σ8. We also show measurements from data from a previous lensing experiment, CFHTLenS (in orange), and the Planck satellite that measures the cosmic microwave background from the early universe (in red), that disagreed with each other. For each data set we show contours that contain 68 percent and 95 percent of the probability, and have marginalized over other cosmological nuisance parameters.

    As light from galaxies billions of light-years away travels to us, it is subtly deflected by the gravitational influence of massive structures along its path. This effect, called weak gravitational lensing, encodes important information about the way the universe expanded and how structure within it grew in the past. This information is key to unlocking the biggest mystery in cosmology, the nature of the accelerated expansion of the universe, an effect called dark energy. The Dark Energy Survey, or DES, seeks answers to this mystery by mapping an eighth of the night sky.

    Dark Energy Icon
    Dark Energy Camera
    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    Dark Energy Survey, the Dark Energy Camera, built at FNAL, and housed in the CTIO 4 meter Victor M Blanco Telescope in Chile

    DES measures weak gravitational lensing signals by correlating the shapes of hundreds of millions of galaxies. The subtle weak lensing deflections by large-scale structure shear the shapes of the galaxies. This effect is tiny — a very small “stretch” to galaxy images that already come in a wide variety of shapes and sizes — and it is only by comparing and correlating these large numbers of galaxies that we can beat down the noise. Even worse, the Earth’s atmosphere and the telescope optics distort the images even more than the signal we are looking for, and these distortions must be carefully removed to uncover the weak lensing signals.

    But if we can beat these challenges, then the coherent pattern of galaxy stretching will provide a map and a history of gravity and the growth of structure in the universe that tells the story of the last 8 billion years of the cosmos.

    Precise shape measurements are not the only requirement for learning about dark energy from DES. The survey must also estimate the distances to all its galaxies, which is done by measuring their redshifts, the fractional stretching of their light due to the expansion of the universe. Because DES takes images in broad color filters, it can see only a very coarse spectrum of the light from each galaxy and so can get only very approximate distances to each galaxy. These photometric redshifts, as they’re called, have their own complexities that must be carefully controlled so that distance errors don’t ruin the constraints on dark energy from DES data.

    This month DES released a collection of papers making these high-precision galaxy shape measurements, understanding the redshifts of the galaxies and using this information to constrain cosmology. This early data set is sensitive mainly to two numbers: the amount of matter in the universe and how much that matter has pulled together gravitationally into the structures that form the skeleton of galaxies and galaxy clusters. Two of the most powerful existing cosmology surveys, the Planck Satellite and Canada-France-Hawaii Telescope [CFHT] Lensing Survey, seem to disagree about these quantities, and the DES measurements sit squarely half way between them.

    ESA Planck
    ESA/Planck

    Canada-France-Hawaii Telescope
    Canada France Hawaii Telescope Interior
    CFHT

    Despite containing millions of galaxies, the data that went into this analysis is only a tiny fraction of the full survey, just a few percent. The final DES data set will be more than 30 times bigger, requiring even more accurate galaxy shape and redshift measurements than what was achieved for this first analysis. When completed and analyzed, DES data will provide powerful new information about the history, contents and likely future of the universe.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Fermilab Campus

    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.

     
  • richardmitnick 11:21 am on May 14, 2015 Permalink | Reply
    Tags: , , Dark Energy Survey, Princeton ACT,   

    From Sky and Telescope: “Mapping Dark Matter” 

    SKY&Telescope bloc

    Sky & Telescope

    May 7, 2015
    Monica Young

    Two projects are mapping the distribution of dark matter in the universe, probing scales both large and small.

    1
    A snapshot from the Bolshoi cosmology simulation shows what the universe’s current dark matter distribution should look like. This box is roughly 800 million light-years across. Anatoly Klypin (NMSU), Joel R. Primack (UCSC), and Stefan Gottloeber (AIP, Germany)

    Observations show the universe to be a cosmic spider web: galaxies and clusters of galaxies are strung along its nodes and filaments like so many caught flies. Yet the thread — dark matter, which makes up 85% of the universe’s mass — is largely invisible, fully visualized only in simulations.

    Scientists are finding ways to map this unseen backbone of the universe, plotting its effect on light coming from distant galaxies and even from the remnant glow of the Big Bang, the cosmic microwave background [CMB].

    Cosmic Microwave Background  Planck
    CMB per ESA/Planck

    ESA Planck
    ESA/Planck

    Two projects making the invisible visible are the Dark Energy Survey, led by Josh Frieman (Fermilab) and conducted at the Cerro Tololo Inter-American Observatory in the Chilean Andes, and the Atacama Cosmology Telescope [ACT] polarization survey, also in Chile and high in the Atacama Desert. These complementary surveys are taking on the universe on scales big and small.

    Dark Energy Camera
    DECam, built at FNAL
    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO Victor M Blanco telescope, which houses the DECam

    Princeton ACT Telescope
    ACT

    Mapping Superclusters and Supervoids

    2
    By measuring dark matter’s smearing effect on galaxy shapes, the Dark Energy Survey mapped out the mysterious stuff’s density over a 139-square-degree swath of sky. The color scale reflects dark matter density; grey circles mark galaxy clusters – bigger circles represent larger clusters.
    Dark Energy Survey

    Frieman’s team is tackling the large-scale universe using the Dark Energy Camera, a 570-megapixel CCD camera that’s in the process of surveying a huge, 5,000-square-degree swath of Southern Hemisphere sky. (Compare that to the cutting-edge yet still-measly 16-megapixel camera in a Samsung Galaxy S6 smartphone!)

    Using preliminary data that covers just 3% of the full survey, a team led by Vinu Vikram (Argonne National Laboratory) examined the shapes of more than 1 million faraway galaxies, whose light has traveled between 5.8 billion and 8.5 billion years to reach us. The team was looking for the smearing effect of intervening dark matter.

    Dark matter’s gravity acts like a lens to magnify and distort the galaxies’ light, but its effect is weak — individual galaxies vary enough in shape that the gravitational lensing isn’t noticeable. The key is quantity: measure enough galaxies and the smearing becomes plain.

    Vikram and colleagues measured the smearing to construct a two-dimensional dark matter map, plotting out how much dark matter lies along lines of sight within a 139-square-degree area.

    Since the map traces normal, luminous matter (galaxies and galaxy clusters) as well as the now-visible dark matter web, astronomers can use it to study the connection between the two. Galaxies and clusters don’t exactly trace the underlying dark matter distribution, since normal and dark matter follow different physical laws, so knowing how the two differ is essential for puzzling out longstanding mysteries.

    Mapping Galaxies’ Dark Matter Halos

    3
    This stacked image of ACT polarization data shows what a single, average dark matter halo looks like. As blobby as it is, its measurements match predictions from dark matter simulations. M. Madhavacheril & others

    After viewing the grand, 500-million-light-year scales of the Dark Energy Survey results, which still only hint at the mammoth survey to come, zooming into recent observations from the Atacama Cosmology Telescope (ACT) is like taking a sip of the shrinking potion in Alice in Wonderland.

    The ACT dark matter maps focus on a scale of a mere 3 million light-years, roughly the size of a dark matter halo around an individual galaxy. Graduate student Mathew Madhavacheril and his advisor Neelima Sehgal (both Stony Brook University) led a team in measuring dark matter’s smearing effect, not on the light from faraway galaxies, but on the most well-traveled light in the universe: the cosmic microwave background (CMB).

    ACT’s polarimeter spent 3 months surveying the glow from photons freed 380,000 years after the Big Bang at a frequency of 146 GHz (corresponding to a wavelength of 2 millimeters). Even though this glow is “bumpy,” varying in brightness from one spot to the next, it’s actually pretty smooth on the arcminute scales probed by ACT. But a million-light-year-wide hunk of intervening dark matter will distort the light and create sharp changes in brightness on these small scales.

    The team looked for such brightness changes and found about 12,000 that matched up with galaxies listed in a Sloan Digital Sky Survey catalog. Each of these galaxies has a massive halo roughly 10 times that of the Milky Way. Stacking all the ACT images together, the team created an image of an average dark matter halo.

    Simply measuring the signal from galaxies’ dark matter halos is an accomplishment — little has been done on these small scales before. The average dark halo’s mass and concentration, as measured from this blobby image, so far match what’s expected from dark matter simulations. The same technique will be applied to the Advanced ACT polarization survey taking place between 2016 and 2018, which will cover ten times the sky area. Eventually, Madhavacheril hopes to trace the growth of dark matter halos over cosmic time.

    Preliminary as they are, these maps pave the way for understanding dark matter’s role in the universe, including its structure, its connection to ordinary matter, and its role in the evolution and fate of the universe.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

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

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

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 1:05 pm on April 30, 2015 Permalink | Reply
    Tags: , , Dark Energy Survey, ,   

    From Symmetry: “DECam’s far-out forays” 

    Symmetry

    April 30, 2015
    Liz Kruesi

    1
    Photo by Reidar Hahn, Fermilab

    The Dark Energy Camera does even more than its name would lead you to believe.

    The Dark Energy Survey, which studies the accelerating expansion of our universe, uses one of the most sensitive observing tools that astronomers have: the Dark Energy Camera.

    Built at Fermi National Accelerator Laboratory and situated on the Victor Blanco 4-meter telescope in Chile, the camera spends 30 percent of each year collecting light from clusters of galaxies for DES.

    CTIO Victor M Blanco 4m Telescope
    CTIO Victor M Blanco 4m Telescope interior
    CTIO Victor Blanco 4-meter telescope

    Another chunk of time goes to engineering and upgrades. The remaining one-third is split up among dozens of other observing projects.

    A recent symmetry article looked at some of those projects—the ones that are studying objects within our solar system. In this follow-up, we give a sampling of how DECam has been used to reach even farther into the universe.

    Studying stellar oddballs

    The sun is a “normal” star, humming along, fusing hydrogen to helium in its core. Most of the stars in the universe produce energy this way. But the cosmos contains a whole collection of stranger stellar objects, such as white dwarfs, brown dwarfs and neutron stars. They also include exploding stars called supernovae. Ten projects use the DECam to study these stellar varieties.

    Armin Rest, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland, leads two of those projects. In the past two years, he has spent 28 nights at the Blanco Telescope looking for supernovae.

    In both projects, Rest looks for light released during stellar explosions that has bounced off dust clouds on its way to our night sky. These “light echoes” preserve information about the blasts that caused them—for example, what type of star exploded and how it exploded.

    “It is as if we have a time machine with which we can travel back in time and take a spectrum with modern instrumentation of an event that was seen on Earth hundreds of years ago,” Rest says.

    DECam’s expertise in taking fast pictures of big areas makes this search much more efficient than it would be with other instruments, Rest says.

    Following streams of stars

    Astronomers have found many streams of stars winding tens of degrees across our sky. These streams are the telltale signs of galaxies interacting with one another. The gravity of one galaxy can rip the stars out of another.

    Yale University’s Ana Bonaca is working on a project that uses DECam to map the stars in one such stream. It extends from Palomar 5, a conglomeration of thousands of stars at the outskirts of our galaxy. Palomar 5 is one of the lowest-mass objects being torn apart by the Milky Way, “which means that its streams are very narrow and preserve a better record of past interactions,” Bonaca says.

    2
    Palomar 5

    Scientists are hoping to tease out of these observations information about dark matter, which accounts for some 80 to 90 percent of our galaxy’s mass.

    Scientists expect that in a narrow stellar stream, clumps of dark matter will create density variations. If you can map the density variations in such a stream, you can learn how the dark matter is distributed. This is where DECam’s strength comes in: The sensitive instrument collects light from deep imaging across large fields speckled with long, narrow stellar streams.

    Ten other projects are using the instrument for similar research.

    Bonaca and colleagues expect to publish their findings later this year. “Our preliminary maps of the Palomar 5 stream show tantalizing evidence for density variations along the stream,” she says.

    Digging for galaxies

    Our galaxy is just one of at least 100 billion galaxies in the universe. Those other galaxies are the focus of eight projects using the Dark Energy Camera.

    The DECam Legacy Survey, for one, is currently imaging all of the galaxies in 6700 square degrees of sky. The plan, says David Schlegel of the Lawrence Berkeley National Laboratory, is to combine the information gathered from DECam and two telescopes located at Arizona’s Kitt Peak National Observatory with the images, spectral data and distance measurements collected via the long-running Sloan Digital Sky Survey.

    “The combination of the Legacy Survey imaging plus SDSS spectroscopy will be used for studying the evolution of galaxies, the halo of our Milky Way and other things we’ve likely not thought of yet,” Schlegel says.

    SDSS Telescope
    SDSS Telescope at Apache Moint, NM, USA

    The other goal of the survey is to identify some 30 million targets to study with the Dark Energy Spectroscopic Instrument [DESI}, a recently approved instrument that will be installed on the Mayall 4-meter telescope at Kitt Peak.

    NOAO Mayall 4 m telescope exterior
    NOAO Mayall 4 m telescope interior
    Mayall 4-meter telescope

    Dark Energy Spectroscopic Instrument
    DESI

    Members of the Legacy Survey team have been releasing their observations nearly immediately to other researchers and the public. They have much more observing time ahead of them: In total, the project was awarded 65 nights on the Blanco telescope and DECam. So far they’ve used only 22.

    Weighing the clusters

    Most of the galaxies in our universe are gathered in groups and clusters, drawn together by the gravity of the clumps of dark matter in which they formed. Scientists are using DECam to study how matter (including dark matter) is distributed within clusters holding hundreds to thousands of galaxies.

    When you observe a galaxy cluster, you also collect light from objects that lie behind that cluster. In the same way an old, imperfect window warps the light from a streetlamp, a cluster’s galaxies, gas, and dark matter shear and stretch any background light that passes through. Astronomers analyze this bending of light from background galaxies, an effect called “gravitational lensing,” to map the mass distribution of a galaxy cluster and even measure its total mass.

    Seven projects use the DECam for such studies. Ian Dell’Antonio of Brown University leads one of them. He and colleagues study the 10 largest galaxy clusters that fit within the DECam field of view; all of them are between about 500 million and 1.4 billion light-years from Earth.

    The researchers are about halfway through their dozen observing nights. They have so far differentiated between gravitational lensing by galaxy cluster Abell 3128 and gravitational lensing by another background cluster. They estimate the mass of Abell 3128 is about 1000 trillion times the mass of our sun, and they have identified several clumps of dark matter, Dell’Antonio says.

    The Dark Energy Camera’s large field of view is crucial to this research, but so is the camera’s design, Dell’Antonio says. “DECam was designed to have an unusually uniform focus across the field of view and with special detectors to keep the camera in focus throughout the night. Put all these things together, and you’ve got an excellent camera for gravitational lensing studies.”

    And, it seems, for just about any other type of astronomical imaging scientists can think of.

    See the full article here.

    Please help promote STEM in your local schools.

    STEM Icon

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    Symmetry is a joint Fermilab/SLAC publication.


     
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