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  • richardmitnick 2:35 pm on February 20, 2019 Permalink | Reply
    Tags: "In Colliding Galaxies a Pipsqueak Shines Bright", A much smaller object is competing with the two behemoths, , , At the center of each galaxy is a supermassive black hole millions of times more massive than the Sun, , Collectively known as Messier 51 the two galaxies are merging, , , , Neither black hole is radiating as brightly in the X-ray range as scientists would expect during a merger, SDSS, The neutron star found in Messier 51 is even brighter than average and belongs to a newly discovered class known as ultraluminous neutron stars, The small X-ray source is a neutron star, Two supermassive black holes heat up and devour surrounding material, Whirlpool galaxy a.k.a. Messier 51a M51 and NGC 5194 and its companion galaxy Messier 51b   

    From JPL-Caltech: “In Colliding Galaxies, a Pipsqueak Shines Bright” 

    NASA JPL Banner

    From JPL-Caltech

    February 20, 2019

    Calla Cofield
    Jet Propulsion Laboratory, Pasadena, Calif.
    626-808-2469
    calla.e.cofield@jpl.nasa.gov

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    Bright green sources of high-energy X-ray light captured by NASA’s NuSTAR mission are overlaid on an optical-light image of the Whirlpool galaxy a.k.a. Messier 51a, M51a, and NGC 5194 (in the center of the image) and its companion galaxy, Messier 51b (the bright greenish-white spot above the Whirlpool), taken by the Sloan Digital Sky Survey.Credit: NASA/JPL-Caltech, IPAC

    NASA/DTU/ASI NuSTAR X-ray telescope

    SDSS 2.5 meter Telescope at Apache Point Observatory, near Sunspot NM, USA, Altitude 2,788 meters (9,147 ft)

    In the nearby Whirlpool galaxy and its companion galaxy, Messier 51b, two supermassive black holes heat up and devour surrounding material. These two monsters should be the most luminous X-ray sources in sight, but a new study using observations from NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) mission shows that a much smaller object is competing with the two behemoths.

    The most stunning features of the Whirlpool galaxy – officially known as Messier 51a – are the two long, star-filled “arms” curling around the galactic center like ribbons. The much smaller Messier 51b clings like a barnacle to the edge of the Whirlpool. Collectively known as Messier 51, the two galaxies are merging.

    At the center of each galaxy is a supermassive black hole millions of times more massive than the Sun. The galactic merger should push huge amounts of gas and dust into those black holes and into orbit around them. In turn, the intense gravity of the black holes should cause that orbiting material to heat up and radiate, forming bright disks around each that can outshine all the stars in their galaxies.

    But neither black hole is radiating as brightly in the X-ray range as scientists would expect during a merger. Based on earlier observations from satellites that detect low-energy X-rays, such as NASA’s Chandra X-ray Observatory, scientists believed that layers of gas and dust around the black hole in the larger galaxy were blocking extra emission. But the new study, published in The Astrophysical Journal, used NuSTAR’s high-energy X-ray vision to peer below those layers and found that the black hole is still dimmer than expected.

    “I’m still surprised by this finding,” said study lead author Murray Brightman, a researcher at Caltech in Pasadena, California. “Galactic mergers are supposed to generate black hole growth, and the evidence of that would be strong emission of high-energy X-rays. But we’re not seeing that here.”

    Brightman thinks the most likely explanation is that black holes “flicker” during galactic mergers rather than radiate with a more or less constant brightness throughout the process.

    “The flickering hypothesis is a new idea in the field,” said Daniel Stern, a research scientist at NASA’s Jet Propulsion Laboratory in Pasadena and the project scientist for NuSTAR. “We used to think that the black hole variability occurred on timescales of millions of years, but now we’re thinking those timescales could be much shorter. Figuring out how short is an area of active study.”

    Small but Brilliant

    Along with the two black holes radiating less than scientists anticipated in Messier 51a and Messier 51b, the former also hosts an object that is millions of times smaller than either black hole yet is shining with equal intensity. The two phenomena are not connected, but they do create a surprising X-ray landscape in Messier 51.

    The small X-ray source is a neutron star, an incredibly dense nugget of material left over after a massive star explodes at the end of its life. A typical neutron star is hundreds of thousands of times smaller in diameter than the Sun – only as wide as a large city – yet has one to two times the mass. A teaspoon of neutron star material would weigh more than 1 billion tons.

    Despite their size, neutron stars often make themselves known through intense light emissions. The neutron star found in M51 is even brighter than average and belongs to a newly discovered class known as ultraluminous neutron stars. Brightman said some scientists have proposed that strong magnetic fields generated by the neutron star could be responsible for the luminous emission; a previous paper by Brightman and colleagues about this neutron star supports that hypothesis. Some of the other bright, high-energy X-ray sources seen in these two galaxies could also be neutron stars.

    NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corporation in Dulles, Virginia (now part of Northrop Grumman). NuSTAR’s mission operations center is at UC Berkeley, and the official data archive is at NASA’s High Energy Astrophysics Science Archive Research Center. ASI provides the mission’s ground station and a mirror archive.

    See the full article here .


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    NASA JPL Campus

    Jet Propulsion Laboratory (JPL) is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. Although the facility has a Pasadena postal address, it is actually headquartered in the city of La Cañada Flintridge, on the northwest border of Pasadena. JPL is managed by the nearby California Institute of Technology (Caltech) for the National Aeronautics and Space Administration. The Laboratory’s primary function is the construction and operation of robotic planetary spacecraft, though it also conducts Earth-orbit and astronomy missions. It is also responsible for operating NASA’s Deep Space Network.

    Caltech Logo

    NASA image

     
  • richardmitnick 12:36 pm on December 27, 2018 Permalink | Reply
    Tags: APOGEE South spectrograph, , , , , , , SDSS   

    From Science Blog from the SDSS: “SDSS Fifteenth Data Release” 

    SDSS Science blog bloc

    From Science Blog from the SDSS

    On Monday 10 December the Sloan Digital Sky Survey (SDSS) celebrated its fifteenth public data release, DR15. This data release the spotlight was on the MaNGA survey (Mapping Nearby Galaxies at Apache Point Observatory).

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    DR15 contains 4621 of the 10,000 galaxies that MaNGA will have observed by summer 2020. To keep up to date with all MaNGA news, you can follow this survey on twitter: @MaNGASurvey. Image credit: Dana Berry / SkyWorks Digital Inc., David Law, and the SDSS collaboration.

    MaNGA observes nearby galaxies using a technique called Integral-Field Spectroscopy. This technique allows them to take many spectra all across the galaxy, and these spectra are then used to map the stars and gas in the galaxy. MaNGA can then find out how the stars and gas move around in the galaxy, and what kind of stellar populations (young? old? metal-rich? metal-poor?) are present in the galaxy. These maps help the MaNGA team understand how galaxies form and evolve over cosmic time. DR15 includes all these maps, that were produced by a special Data Analysis Pipeline, and with Marvin you can now explore these maps yourself!

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    Caption: snapshot of Marvin: the new tool to explore MaNGA galaxies. You can find Marvin at https://dr15.sdss.org/marvin/, and you can also follow Marvin on twitter: @Marvin_SDSS. Image taken from Aguado et al. 2018.

    But it was not just galaxies that featured in DR15: MaNGA is running a sub-program called MaStar: the MaNGA Stellar Library.

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    Example spectra from the MaStar library.

    This survey observes almost in stealth mode: they use the optical BOSS spectrographs that MaNGA also uses, but only when there is a full moon and the sky is too bright to observe faint galaxies. Bright time is when APOGEE-2 is in charge, using the Sloan telescope to observe Milky Way stars in the infrared.

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    But the MaStar and APOGEE-2 teams work together, so that both teams can observe their stars at the same time using two different spectrographs (optical and infrared). The MaStar team is interested in learning more about the properties and physics of their stars, but also want to use their stellar spectra as templates for analyzing MaNGA galaxies.

    All this new data is now freely available, and we have a brand-new portal to show you all the different ways that you can access and interact with SDSS data: https://dr15.sdss.org/. A very big thank you to all the people in SDSS who made DR15 possible, and a special shout-out to all SDSS team members last spring participated in DocuVana, to write all the documentation that goes with this data release!

    What is next? MaNGA’s sibling surveys, APOGEE-2 (APO Galaxy Evolution Experiment 2) and eBOSS (Extended Baryon Oscillation Spectroscopic Survey) took a break during DR15, because they are preparing for a smashing DR16. Next year APOGEE-2 will release lots of new infra-red spectra of stars in the Milky Way, including the very first spectra taken from the Southern hemisphere at Las Campanas Observatory. And eBOSS is currently hard at work putting together new catalogs of the large scale structure of the Universe, that they will release alongside lots of new optical spectra of galaxies and quasars. So stay tuned for DR16!

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    The “first light” observations for the APOGEE South spectrograph. The dots show stars whose spectra were observed by APOGEE. Some example spectra are shown (colors are representative only, as APOGEE spectra are in the infrared).

    The first light observations included spectra of supermassive stars in the Tarantula Nebula. This nebula in the Large Magellanic Cloud is forming stars more rapidly than any other region in our Local Group of galaxies. It can only be seen from the Southern Hemisphere, underscoring the importance of APOGEE South’s location. The spectrograph will allow us to study the chemistry and evolution of the stars in the nebula in greater detail than ever before.

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    A slice through largest-ever three-dimensional map of the Universe. Earth is at the left, and distances to galaxies and quasars are labelled by the lookback time to the objects (lookback time means how long the light from an object has been traveling to reach us here on Earth). The locations of quasars (galaxies with supermassive black holes) are shown by the red dots, and nearer galaxies mapped by SDSS are also shown (yellow).

    The right-hand edge of the map is the limit of the observable Universe, from which we see the Cosmic Microwave Background (CMB) – the light “left over” from the Big Bang. The bulk of the empty space in between the quasars and the edge of the observable universe are from the “dark ages”, prior to the formation of most stars, galaxies, or quasars. Click on the image for a larger version.

    Image Credit: Anand Raichoor (École polytechnique fédérale de Lausanne, Switzerland) and the SDSS collaboration

    See the full article here .

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

    After nearly a decade of design and construction, the Sloan Digital Sky Survey saw first light on its giant mosaic camera in 1998 and entered routine operations in 2000. While the collaboration and scope of the SDSS have changed over the years, many of its key principles have stayed fixed: the use of highly efficient instruments and software to enable astronomical surveys of unprecedented scientific reach, a commitment to creating high quality public data sets, and investigations that draw on the full range of expertise in a large international collaboration. The generous support of the Alfred P. Sloan Foundation has been crucial in all phases of the SDSS, alongside support from the Participating Institutions and national funding agencies in the U.S. and other countries.

    The Sloan Digital Sky Survey has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one third of the sky, and spectra for more than three million astronomical objects.

    In its first five years of operations, the SDSS carried out deep multi-color imaging over 8000 square degrees and measured spectra of more than 700,000 celestial objects. With an ever-growing collaboration, SDSS-II (2005-2008) completed the original survey goals of imaging half the northern sky and mapping the 3-dimensional clustering of one million galaxies and 100,000 quasars. SDSS-II carried out two additional surveys: the Supernova Survey, which discovered and monitored hundreds of supernovae to measure the expansion history of the universe, and the Sloan Extension for Galactic Understanding and Exploration (SEGUE), which extended SDSS imaging towards the plane of the Galaxy and mapped the motions and composition of more than a quarter million Milky Way stars.

    SDSS-III (2008-2014) undertook a major upgrade of the venerable SDSS spectrographs and added two powerful new instruments to execute an interweaved set of four surveys, mapping the clustering of galaxies and intergalactic gas in the distant universe (BOSS), the dynamics and chemical evolution of the Milky Way (SEGUE-2 and APOGEE), and the population of extra-solar giant planets (MARVELS).

    The latest generation of the SDSS (SDSS-IV, 2014-2020) is extending precision cosmological measurements to a critical early phase of cosmic history (eBOSS), expanding its revolutionary infrared spectroscopic survey of the Galaxy in the northern and southern hemispheres (APOGEE-2), and for the first time using the Sloan spectrographs to make spatially resolved maps of individual galaxies (MaNGA).

    This is the “Science blog” of the SDSS. Here you’ll find short descriptions of interesting scientific research and discoveries from the SDSS. We’ll also update on activities of the collaboration in public engagement and other arenas. We’d love to see your comments and questions about what you read here!

    You can explore more on the SDSS Website.

     
  • richardmitnick 5:48 pm on December 17, 2018 Permalink | Reply
    Tags: A Repository for Large Sets of Valuable Scientific Data, , , HEPCloud, Pushing the Envelope on High-Throughput Computing, SDSS   

    From Fermi National Accelerator Lab via HostingAdvice.com: “The World-Class Computing Resources Behind the DOE’s Fermilab” 

    FNAL II photo

    FNAL Art Image
    FNAL Art Image by Angela Gonzales

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

    via

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    HostingAdvice.com

    December 14, 2018
    Christine Preusler

    Fermilab, a DOE-sponsored particle physics and accelerator laboratory, is raising the bar on innovative and cost-effective computing solutions that help researchers explore high-energy physics. As a repository for massive sets of scientific data, the national laboratory is at the forefront of new computing approaches, including HEPCloud, a paradigm for provisioning computing resources.

    It’s common knowledge that Tim Berners-Lee invented the World Wide Web in 1989. But if you’re not a quantum physicist, you may be surprised to learn that he accomplished the feat while working at the European Organization for Nuclear Research (CERN), a prominent scientific organization that operates the largest particle physics lab on the globe.

    “It was the field of high-energy physics for which the web was started to provide a way for physicists to exchange documents,” said Marc Paterno, Assistant Head for R&D and Architecture at Fermilab, a premier national laboratory for particle physics and accelerator research that serves as the American counterpart to CERN.

    Marc told us the particle physics field as a whole has been testing the limits of large-scale data analyzation since it first gained access to high-throughput computational resources. Furthermore, the high-energy physics community is responsible for developing some of the first software and computing tools suitable to meet the demands of the field.

    “Of course, Google has now surpassed us in that its data is bigger than any particular set of experimental data; but even a small experiment at Fermilab produces tens of terabytes of data, and the big ones we are involved with produce hundreds of thousands of petabytes of data over the course of the experiment,” Marc said. “Then there are a few thousand physicists wanting to do analysis on that data.”

    The lab is named after Nobel Prize winner Enrico Fermi, who made significant contributions to quantum theory and created the world’s first nuclear reactor. Located near Chicago, Fermilab is one of 17 U.S. Department of Energy Office of Science laboratories across the country. Though many DOE-funded labs serve multiple purposes, Marc said Fermilab works toward a single mission: “To bring the world together to solve the mysteries of matter, energy, space, and time.”

    And that mission, he said, is made possible through high-powered computing. “For scientists to understand the huge amounts of raw information coming from particle physics experiments, they must process, analyze, and compare the information to simulations,” Marc said. “To accomplish these feats, Fermilab hosts high-performance computing, high-throughput (grid) computing, and storage and networking systems.”

    In addition to leveraging high-performance computing systems to analyze complex datasets, Fermilab is a repository for massive sets of priceless scientific data. With plans to change the way computing resources are used to produce experimental results through HEPCloud, Fermilab is continuing to deploy innovative computing solutions to support its overarching scientific mission.

    Pushing the Envelope on High-Throughput Computing

    While Fermilab wasn’t built to develop computational resources, Marc told us “nothing moves forward in particle physics without computing.” That wasn’t always the case: When the lab was first founded, bubble chambers were used to detect electrically charged particles.

    “They were analyzed by looking at pictures of the bubble chamber, taking a ruler, and measuring curvatures of trails to figure out what the particles were doing inside of a detector,” he said. “Now, detectors are enormous, complicated contraptions that cost tens of millions to billions of dollars to make.”

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    Experiments at Fermilab typically involve massive datasets.

    Marc said Fermilab is in possession of a large amount of computing resources and is heavily involved with CERN’s Compact Muon Solenoid (CMS), a general-purpose detector at the world’s largest and most powerful particle accelerator, the Large Hadron Collider (LHC).

    CERN/CMS Detector

    LHC

    CERN map


    CERN LHC Tunnel

    CERN LHC particles

    The CMS has an extensive physics agenda ranging from researching the Standard Model of particle physics to searching for extra dimensions and particles that possibly make up dark matter.

    The Standard Model of elementary particles (more schematic depiction), with the three generations of matter, gauge bosons in the fourth column, and the Higgs boson in the fifth.


    Standard Model of Particle Physics from Symmetry Magazine

    “Fermilab provides one of the largest pools of resources for the CMS experiment and their worldwide collection,” Marc said.

    Almost every experiment at Fermilab includes significant international involvement from universities and laboratories in other countries. “Fermilab’s upcoming Deep Underground Neutrino Experiment (DUNE) for neutrino science and proton decay studies, for example, will feature contributions from scientists in dozens of countries,” Marc said.

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

    These international particle physics collaborations require Fermilab to transport large amounts of data around the globe quickly through high-throughput computing. To that end, Fermilab features 100Gbit connectivity with local, national, and international networks. The technology empowers researchers to quickly process these data to facilitate scientific discoveries.

    A Repository for Large Sets of Valuable Scientific Data

    Marc told us Fermilab also has mind-boggling storage capacity. “We’re the primary repository for all the data for all of the experiments here at the laboratory,” he said.

    Fermilab’s tape libraries, fully automated and manned by robotic arms, provide more than 100 petabytes of storage capacity for data from particle physics and astrophysics experiments. “This includes a copy of the entire CMS experiment dataset and a copy of the dataset for every Fermilab experiment,” Marc said.

    Fermilab also houses the entire dataset of The Sloan Digital Sky Survey (SDSS), a collaborative international effort to build the most detailed 3D map of the universe in existence.

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

    The data-rich project has measured compositions and distances of more than 3 million stars and galaxies and captured multicolor images of one-third of the sky.

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    The lab’s data management capabilities protect precious scientific data.

    “SDSS was the first time there was an astronomical survey in which all data were digitized, much bigger than any survey done before,” Marc said. “In fact, even though the data collection has stopped, people are still actively using that dataset for current analysis.”

    Marc said much of the particle physics research is done in concert with the academic community and can involve a significantly lengthy process.

    “For example, the DUNE experiment is a worldwide collaboration that researchers have been developing for more than 10 years,” he said. “We are starting on the facility where the detector will go. The lifetime of a big experiment these days is measured in tens of years; even a small experiment with 100 collaborators easily takes 10 years to move forward.”

    HEPCloud: A New Paradigm for Provisioning Computing Resources
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    HEPCloud will enable scientists to put computing resources to better use.

    Particle physics has historically required extensive computing resources from sources such as local batch farms, grid sites, private clouds, commercial clouds, and supercomputing centers — plus the knowledge required to access and use the resources efficiently. Marc told us all that changes with HEPCloud, a new paradigm Fermilab is pursuing in particle physics computing. The HEPCloud facility will allow Fermilab to provision computing resources through a single managed portal efficiently and cost-effectively.

    “HEPCloud is a significant initiative to both simplify how we use these systems and make the process more cost-effective,” Marc said. “Here at Fermilab, trying to provision enough resources to meet demand peaks is just too expensive, and when we’re not on peak, there’d be lots of unused resources.”

    The technology will change the way physics experiments use computing resources by elastically expanding resource pools on short notice — for example, by renting temporary resources on commercial clouds. This will allow the facility to respond to peaks without over-provisioning local resources.

    “HEPCloud is not a cloud provider,” Marc said. “It’s an intelligent brokerage system that can take a request for a certain amount of resources with a certain amount of data; a portal to use cloud resources, the open science grid, and even supercomputing centers such as the National Energy Research Scientific Computing Center (NERSC).”

    Marc said the DOE funds a number of supercomputing sites across the country, and Fermilab’s goal is to make better use of those resources. “It’s not feasible for us to keep on growing larger with traditional computing resources,” Marc said. “So a good deal of our applied computing research is looking at how to do the kind of analysis we need to do on those machines.”

    At the end of the day, Marc recognizes the importance of letting the public know how scientists, engineers, and programmers at Fermilab are tackling today’s most challenging computational problems. “This is taxpayer money, and we ought to be able to provide evidence that what we are doing is valuable and should be supported,” he said.

    Ultimately, its solutions will help America stay at the forefront of innovation.

    See the full article here .


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    FNAL Icon

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


    FNAL/MINERvA

    FNAL DAMIC

    FNAL Muon g-2 studio

    FNAL Short-Baseline Near Detector under construction

    FNAL Mu2e solenoid

    Dark Energy Camera [DECam], built at FNAL

    FNAL DUNE Argon tank at SURF

    FNAL/MicrobooNE

    FNAL Don Lincoln

    FNAL/MINOS

    FNAL Cryomodule Testing Facility

    FNAL Minos Far Detector

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

    FNAL/NOvA experiment map

    FNAL NOvA Near Detector

    FNAL ICARUS

    FNAL Holometer

     
  • richardmitnick 12:53 pm on March 28, 2018 Permalink | Reply
    Tags: "Dark Matter is a No Show in Ghostly Galaxy, , , , , , Gemini Multi Object Spectrograph (GMOS) on Gemini North on Hawai‘i’s Maunakea, , Keck DIEMOS on Keck 2, , , NGC1052-DF2, SDSS   

    From Gemini and Keck: “Dark Matter is a No Show in Ghostly Galaxy” 

    NOAO

    Gemini Observatory
    Gemini Observatory

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


    Keck Observatory

    Science Contacts:

    Pieter van Dokkum
    Astronomy Department
    Yale University
    pieter.vandokkum@yale.edu
    Phone: 203-432-5048

    Shany Danieli
    Astronomy Department
    Yale University
    shany.danieli@yale.edu
    Phone: 857-919-3674

    Media Contacts:

    Mari-Ela Chock
    W.M. Keck Observatory
    mchock@keck.hawaii.edu
    Phone: 808-554-0567

    Jasmin Silva
    Gemini Observatory
    jsilva@gemini.edu
    Desk: 808 974-2575

    1
    Composite color image of NGC1052-DF2 constructed from observations using the Gemini Multi Object Spectrograph (GMOS) on Gemini North on Hawai‘i’s Maunakea. The ultra-diffuse galaxy was observed using deep imaging in two filters (g’ and i’). Image credit: Gemini Observatory/NSF/AURA/Keck/Jen Miller.

    GEMINI North GMOS

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    Left: The ultra-diffuse galaxy is swarming with globular clusters, which hold the key to understanding this mysterious object’s origin and mass.
    Right: A closer look at one of the globular clusters within the galaxy, which are all much brighter than typical, the brightest emitting almost as much light as the brightest within the Milky Way. The spectrum, obtained by Keck Observatory shows the absorption lines used to determine the velocity of this object. Ten clusters were observed, providing the information needed to determine the mass of the galaxy, revealing its lack of dark matter. Image credit: Gemini Observatory/NSF/AURA/Keck/Jen Miller/Joy Pollard.

    Astronomers using data from the Gemini and W. M. Keck Observatories in Hawai‘i have encountered a galaxy that appears to have almost no dark matter. Since the Universe is dominated by dark matter, and it is the foundation upon which galaxies are built, “…this is a game changer,” according to Principal Investigator Pieter van Dokkum of Yale University.

    Galaxies and dark matter go hand in hand; you typically don’t find one without the other. So when researchers uncovered a galaxy, known as NGC1052-DF2, that is almost completely devoid of the stuff, they were shocked.

    “Finding a galaxy without dark matter is unexpected because this invisible, mysterious substance is the most dominant aspect of any galaxy,” said lead author Pieter van Dokkum of Yale University. “For decades, we thought that galaxies start their lives as blobs of dark matter. After that everything else happens: gas falls into the dark matter halos, the gas turns into stars, they slowly build up, then you end up with galaxies like the Milky Way. NGC1052-DF2 challenges the standard ideas of how we think galaxies form.”

    The research, published in the March 29th issue of the journal Nature, amassed data from the Gemini North and W. M. Keck Observatories, both on Maunakea, Hawai‘i, the Hubble Space Telescope, and other telescopes around the world.

    NASA/ESA Hubble Telescope

    Given its large size and faint appearance, astronomers classify NGC1052-DF2 as an ultra-diffuse galaxy, a relatively new type of galaxy that was first discovered in 2015. Ultra-diffuse galaxies are surprisingly common. However, no other galaxy of this type yet-discovered is so lacking in dark matter.

    “NGC1052-DF2 is an oddity, even among this unusual class of galaxy,” said Shany Danieli, a Yale University graduate student on the team.

    To peer even deeper into this unique galaxy, the team used the Gemini Multi Object Spectrograph (GMOS) to capture detailed images of NGC1052-DF2, assess its structure, and confirm that the galaxy had no signs of interactions with other galaxies.

    “Without the Gemini images dissecting the galaxy’s morphology we would have lacked context for the rest of the data,” said Danieli. “Also, Gemini’s confirmation that NGC1052-DF2 is not currently interacting with another galaxy will help us answer questions about the conditions surrounding its birth.”

    Van Dokkum and his team first spotted NGC1052-DF2 with the Dragonfly Telephoto Array, a custom-built telescope in New Mexico that they designed to find these ghostly galaxies.

    U Toronta Dragon Fly Telescope Array housed in New Mexico

    NGC1052-DF2 stood out in stark contrast when comparisons were made between images from the Dragonfly Telephoto Array and the Sloan Digital Sky Survey (SDSS).

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

    The Dragonfly images show a faint “blob-like” object, while SDSS data reveal a collection of relatively bright point-like sources.

    In addition to the Gemini observations, to further assess this inconsistency the team dissected the light from several of the bright sources within NGC1052-DF2 using Keck’s Deep Imaging Multi-Object Spectrograph (DEIMOS) and Low-Resolution Imaging Spectrometer (LRIS), identifying 10 globular clusters. These clusters are large compact groups of stars that orbit the galactic core.

    Keck/DEIMOS on Keck 2

    Keck LRIS

    The spectral data obtained on the Keck telescopes revealed that the globular clusters were moving much slower than expected. The slower the objects in a system move, the less mass there is in that system. The team’s calculations show that all of the mass in the galaxy could be attributed to the mass of the stars, which means there is almost no dark matter in NGC1052-DF2.

    “If there is any dark matter at all, it’s very little,” van Dokkum explained. “The stars in the galaxy can account for all of the mass, and there doesn’t seem to be any room for dark matter.”

    The team’s results demonstrate that dark matter is separable from galaxies. “This discovery shows that dark matter is real – it has its own separate existence apart from other components of galaxies,” said van Dokkum.

    NGC1052-DF2’s globular clusters and atypical structure has perplexed astronomers aiming to determine the conditions this galaxy formed under.

    “It’s like you take a galaxy and you only have the stellar halo and globular clusters, and it somehow forgot to make everything else,” van Dokkum said. “There is no theory that predicted these types of galaxies. The galaxy is a complete mystery, as everything about it is strange. How you actually go about forming one of these things is completely unknown.”

    However, researchers do have some ideas. NGC1052-DF2 resides about 65 million light years away in a collection of galaxies that is dominated by the giant elliptical galaxy NGC 1052. Galaxy formation is turbulent and violent, and van Dokkum suggests that the growth of the fledgling massive galaxy billions of years ago perhaps played a role in NGC1052-DF2’s dark-matter deficiency.

    Another idea is that a cataclysmic event within the oddball galaxy, such as the birth of myriad massive stars, swept out all the gas and dark matter, halting star formation.

    These possibilities are speculative, however, and don’t explain all of the characteristics of the observed galaxy, the researchers add.

    The team continues the hunt for more dark-matter-deficient galaxies. They are analyzing Hubble images of 23 other diffuse galaxies. Three of them appear to share similarities with NGC1052-DF2, which van Dokkum plans to follow up on in the coming months at Keck Observatory.

    “Every galaxy we knew about before has dark matter, and they all fall in familiar categories like spiral or elliptical galaxies,” van Dokkum said. “But what would you get if there were no dark matter at all? Maybe this is what you would get.”

    See the full article here .

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

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


    Keck UCal

    Gemini/North telescope at Maunakea, Hawaii, USA,4,207 m (13,802 ft) above sea level

    Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile, at an altitude of 7200 feet

    AURA Icon

    Gemini’s mission is to advance our knowledge of the Universe by providing the international Gemini Community with forefront access to the entire sky.

    The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai’i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

    The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country’s contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, and the Brazilian Ministério da Ciência, Tecnologia e Inovação. The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.

     
  • richardmitnick 9:53 am on February 22, 2018 Permalink | Reply
    Tags: , , , , , SDSS   

    From Science Blog from the SDSS: “APOGEE and Amateur Spectroscopy” 

    SDSS Science blog bloc

    Science Blog from the SDSS

    February 17, 2018
    David Whelan

    1
    Drew Chojnowski, APOGEE plate designer and lead of the emission-line stars science group, discusses SDSS and Be stars observed with the APOGEE instrument.

    This weekend, APOGEEans David Whelan and Drew Chojnowski attended the Sacramento Mountains Spectroscopy Workshop. The workshop’s goal? To get amateur astronomers interested in pursuing spectroscopy. With a mix of amateurs and professionals in the room, the expertise was readily available, and the excitement was palatable.

    On Friday, David Whelan lead a discussion on spectral classification of intermediate- and high-mass stars. This is a science effort that is essential to both APOGEE’s emission-line stars group and high-mass stars studies more generally. Perhaps some knowledgeable amateurs can begin to contribute?

    Then on Saturday, Drew introduced the group to observing with the Sloan Telescope. Below, he is shown with one of SDSS’s APOGEE plates.

    2
    Drew and an APOGEE plate – teaching people how the SDSS is done.

    These kinds of workshops break down the barrier between the amateur and the professional, and opens both groups to new possibilities. With special thanks to the organizers Ken Hudson and Joe Daglen, as well as François Cochard from Shelyak Instruments, we very much look forward to pursuing the science generated by this workshop.

    3
    Amateur astronomer Joe Daglen, center, tells workshop attendants about the equipment that he uses to teach undergraduate students about imaging and spectroscopy.

    See the full article here .

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

    After nearly a decade of design and construction, the Sloan Digital Sky Survey saw first light on its giant mosaic camera in 1998 and entered routine operations in 2000. While the collaboration and scope of the SDSS have changed over the years, many of its key principles have stayed fixed: the use of highly efficient instruments and software to enable astronomical surveys of unprecedented scientific reach, a commitment to creating high quality public data sets, and investigations that draw on the full range of expertise in a large international collaboration. The generous support of the Alfred P. Sloan Foundation has been crucial in all phases of the SDSS, alongside support from the Participating Institutions and national funding agencies in the U.S. and other countries.

    The Sloan Digital Sky Survey has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one third of the sky, and spectra for more than three million astronomical objects.

    In its first five years of operations, the SDSS carried out deep multi-color imaging over 8000 square degrees and measured spectra of more than 700,000 celestial objects. With an ever-growing collaboration, SDSS-II (2005-2008) completed the original survey goals of imaging half the northern sky and mapping the 3-dimensional clustering of one million galaxies and 100,000 quasars. SDSS-II carried out two additional surveys: the Supernova Survey, which discovered and monitored hundreds of supernovae to measure the expansion history of the universe, and the Sloan Extension for Galactic Understanding and Exploration (SEGUE), which extended SDSS imaging towards the plane of the Galaxy and mapped the motions and composition of more than a quarter million Milky Way stars.

    SDSS-III (2008-2014) undertook a major upgrade of the venerable SDSS spectrographs and added two powerful new instruments to execute an interweaved set of four surveys, mapping the clustering of galaxies and intergalactic gas in the distant universe (BOSS), the dynamics and chemical evolution of the Milky Way (SEGUE-2 and APOGEE), and the population of extra-solar giant planets (MARVELS).

    The latest generation of the SDSS (SDSS-IV, 2014-2020) is extending precision cosmological measurements to a critical early phase of cosmic history (eBOSS), expanding its revolutionary infrared spectroscopic survey of the Galaxy in the northern and southern hemispheres (APOGEE-2), and for the first time using the Sloan spectrographs to make spatially resolved maps of individual galaxies (MaNGA).

    This is the “Science blog” of the SDSS. Here you’ll find short descriptions of interesting scientific research and discoveries from the SDSS. We’ll also update on activities of the collaboration in public engagement and other arenas. We’d love to see your comments and questions about what you read here!

    You can explore more on the SDSS Website.

     
  • richardmitnick 1:07 pm on January 10, 2018 Permalink | Reply
    Tags: , , , , Direct SMBH mass measurements in galaxies farther away are made using a technique called “reverberation mapping”, farther away, How massive is Supermassive? Astronomers measure more black holes, Key to the success of the SDSS Reverberation Mapping project lies in the SDSS’s ability to study many quasars at once, SDSS,   

    From SDSS: “How massive is Supermassive? Astronomers measure more black holes, farther away” 

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


    Sloan Digital Sky Survey

    January 9, 2018
    Today, astronomers from the Sloan Digital Sky Survey (SDSS) announced new measurements of the masses of a large sample of supermassive black holes far beyond the local Universe.

    1
    An artist’s rendering of the inner regions of an active galaxy/quasar, with a supermassive black hole at the center surrounded by a disk of hot material falling in. The inset at the bottom right shows how the brightness of light coming from the two different regions changes with time.
    The top panel of the plot shows the “continuum” region, which originates close in to the black hole (the general vicinity is indicated by the “swoosh” shape). The bottom panel shows the H-beta emission line region, which comes from fast-moving hydrogen gas farther away from the black hole (the general vicinity is indicated by the other “swoosh”). The time span covered by these two light curves is about six months.
    The bottom plot “echoes” the top, with a slight time delay of about 10 days indicated by the vertical line. This means that the distance between these two regions is about 10 light-days (about 150 billion miles, or 240 million kilometers). Image Credit: Nahks Tr’Ehnl (www.nahks.com) and Catherine Grier (The Pennsylvania State University) and the SDSS collaboration

    The results, being presented at the American Astronomical Society (AAS) meeting in National Harbor, Maryland and published in The Astrophysical Journal, represent a major step forward in our ability to measure supermassive black hole masses in large numbers of distant quasars and galaxies.

    “This is the first time that we have directly measured masses for so many supermassive black holes so far away,” says Catherine Grier, a postdoctoral fellow at the Pennsylvania State University and the lead author of this work. “These new measurements, and future measurements like them, will provide vital information for people studying how galaxies grow and evolve throughout cosmic time.”

    Supermassive Black Holes (SMBHs) are found in the centers of nearly every large galaxy, including those in the farthest reaches of the Universe. The gravitational attraction of these supermassive black holes is so great that nearby dust and gas in the host galaxy is inexorably drawn in. The infalling material heats up to such high temperatures that it glows brightly enough to be seen all the way across the Universe. These bright disks of hot gas are known as “quasars,” and they are clear indicators of the presence of supermassive black holes. By studying these quasars, we learn not only about SMBHs, but also about the distant galaxies that they live in. But to do all of this requires measurements of the properties of the SMBHs, most importantly their masses.

    The problem is that measuring the masses of SMBHs is a daunting task. Astronomers measure SMBH masses in nearby galaxies by observing groups of stars and gas near the galaxy center — however, these techniques do not work for more distant galaxies, because they are so far away that telescopes cannot resolve their centers. Direct SMBH mass measurements in galaxies farther away are made using a technique called “reverberation mapping.”

    Reverberation mapping works by comparing the brightness of light coming from gas very close in to the black hole (referred to as the “continuum” light) to the brightness of light coming from fast-moving gas farther out. Changes occurring in the continuum region impact the outer region, but light takes time to travel outwards, or “reverberate.” This reverberation means that there is a time delay between the variations seen in the two regions. By measuring this time delay, astronomers can determine how far out the gas is from the black hole. Knowing that distance allows them to measure the mass of the supermassive black hole — even though they can’t see the details of the black hole itself.

    Over the past 20 years, astronomers have used the reverberation mapping technique to laboriously measure the masses of around 60 SMBHs in nearby active galaxies. Reverberation mapping requires getting observations of these active galaxies, over and over again for several months — and so for the most part, measurements are made for only a handful of active galaxies at a time. Using the reverberation mapping technique on quasars, which are farther away, is even more difficult, requiring years of repeated observations. Because of these observational difficulties, astronomers had only successfully used reverberation mapping to measure SMBH masses for a handful of more distant quasars — until now.

    3
    A graph of known supermassive black hole masses at various “lookback times,” which measures the time into the past we see when we look at each quasar.
    More distant quasars have longer lookback times (since their light takes longer to travel to Earth), so we see them as they appeared in the more distant past. The Universe is about 13.8 billion years old, so the graph goes back to when the Universe was about half of its current age.
    The black hole masses measured in this work are shown as purple circles, while gray squares show black hole masses measured by prior reverberation mapping projects. The sizes of the squares and circles are related to the masses of the black holes they represent. The graph shows black holes from 5 million to 1.7 billion times the mass of the Sun.
    Image Credit: Catherine Grier (The Pennsylvania State University) and the SDSS collaboration

    In this new work, Grier’s team has used an industrial-scale application of the reverberation mapping technique with the goal of measuring black hole masses in tens to hundreds of quasars. The key to the success of the SDSS Reverberation Mapping project lies in the SDSS’s ability to study many quasars at once — the program is currently observing about 850 quasars simultaneously. But even with the SDSS’s powerful telescope, this is a challenging task because these distant quasars are incredibly faint.

    “You have to calibrate these measurements very carefully to make sure you really understand what the quasar system is doing,” says Jon Trump, an assistant professor at the University of Connecticut and a member of the research team.

    Improvements in the calibrations were obtained by also observing the quasars with the Canada-France-Hawaii-Telescope (CFHT) and the Steward Observatory Bok telescope located at Kitt Peak over the same observing season.


    CFHT, at Maunakea, Hawaii, USA,4,207 m (13,802 ft) above sea level

    Bok Telescope U Arizona Steward Observatory, 2.3-metre Bok Telescope at the Steward Observatory at Kitt Peak in Arizona, USA altitude 2,096 m (6,877 ft)

    After all of the observations were compiled and the calibration process was completed, the team found reverberation time delays for 44 quasars. They used these time delay measurements to calculate black hole masses that range from about 5 million to 1.7 billion times the mass of our Sun.

    “This is a big step forward for quasar science,” says Aaron Barth, a professor of astronomy at the University of California, Irvine who was not involved in the team’s research. “They have shown for the first time that these difficult measurements can be done in mass-production mode.”

    These new SDSS measurements increase the total number of active galaxies with SMBH mass measurements by about two-thirds, and push the measurements farther back in time to when the Universe was only half of its current age. But the team isn’t stopping there — they continue to observe these 850 quasars with SDSS, and the additional years of data will allow them to measure black hole masses in even more distant quasars, which have longer time delays that cannot be measured with a single year of data.

    “Getting observations of quasars over multiple years is crucial to obtain good measurements,” says Yue Shen, an assistant professor at the University of Illinois and Principal Investigator of the SDSS Reverberation Mapping project. “As we continue our project to monitor more and more quasars for years to come, we will be able to better understand how supermassive black holes grow and evolve.”

    The future of the SDSS holds many more exciting possibilities for using reverberation mapping to measure masses of supermassive black holes across the Universe. After the current fourth phase of the SDSS ends in 2020, the fifth phase of the program, SDSS-V, begins. SDSS-V features a new program called the Black Hole Mapper, which plans to measure SMBH masses in more than 1,000 more quasars, pushing farther out into the Universe than any reverberation mapping project ever before.

    “The Black Hole Mapper will let us move into the age of supermassive black hole reverberation mapping on a true industrial scale,” says Niel Brandt, a professor of Astronomy & Astrophysics at the Pennsylvania State University and a long-time member of the SDSS. “We will learn more about these mysterious objects than ever before.”

    See the full article here.

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    The Sloan Digital Sky Survey has created the most detailed three-dimensional maps of the Universe ever made, with deep multi-color images of one third of the sky, and spectra for more than three million astronomical objects. Learn and explore all phases and surveys—past, present, and future—of the SDSS.

    The SDSS began regular survey operations in 2000, after a decade of design and construction. It has progressed through several phases, SDSS-I (2000-2005), SDSS-II (2005-2008), SDSS-III (2008-2014), and SDSS-IV (2014-). Each of these phases has involved multiple surveys with interlocking science goals. The three surveys that comprise SDSS-IV are eBOSS, APOGEE-2, and MaNGA, described at the links below. You can find more about the surveys of SDSS I-III by following the Prior Surveys link.

    Funding for the Sloan Digital Sky Survey IV has been provided by the Alfred P. Sloan Foundation, the U.S. Department of Energy Office of Science, and the Participating Institutions. SDSS- IV acknowledges support and resources from the Center for High-Performance Computing at the University of Utah. The SDSS web site is http://www.sdss.org.

    SDSS-IV is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS Collaboration including the Brazilian Participation Group, the Carnegie Institution for Science, Carnegie Mellon University, the Chilean Participation Group, the French Participation Group, Harvard-Smithsonian Center for Astrophysics, Instituto de Astrofísica de Canarias, The Johns Hopkins University, Kavli Institute for the Physics and Mathematics of the Universe (IPMU) / University of Tokyo, Lawrence Berkeley National Laboratory, Leibniz Institut für Astrophysik Potsdam (AIP), Max-Planck-Institut für Astronomie (MPIA Heidelberg), Max-Planck-Institut für Astrophysik (MPA Garching), Max-Planck-Institut für Extraterrestrische Physik (MPE), National Astronomical Observatory of China, New Mexico State University, New York University, University of Notre Dame, Observatório Nacional / MCTI, The Ohio State University, Pennsylvania State University, Shanghai Astronomical Observatory, United Kingdom Participation Group, Universidad Nacional Autónoma de México, University of Arizona, University of Colorado Boulder, University of Oxford, University of Portsmouth, University of Utah, University of Virginia, University of Washington, University of Wisconsin, Vanderbilt University, and Yale University.

     
  • richardmitnick 5:58 pm on July 18, 2017 Permalink | Reply
    Tags: Ancient Impacts Shaped the Structure of the Milky Way, , , , , SDSS,   

    From Universe Today: “Ancient Impacts Shaped the Structure of the Milky Way” 

    universe-today

    Universe Today

    1
    Accroding to new research, the Milky Way may still bear the marks of “ancient impacts”. Credit: NASA/Serge Brunier.

    18 July , 2017
    Matt Williams

    Understanding how the Universe came to be is one of the greater challenges of being an astrophysicist. Given the observable Universe’s sheer size (46.6 billion light years) and staggering age (13.8 billion years), this is no easy task. Nevertheless, ongoing observations, calculations and computer simulations have allowed astrophysicists to learn a great deal about how galaxies and larger structures have changed over time.

    For example, a recent study by a team from the University of Kentucky (UK) has challenged previously-held notions about how our galaxy has evolved to become what we see today. Based on observations made of the Milky Way’s stellar disk, which was previously thought to be smooth, the team found evidence of asymmetric ripples. This indicates that in the past, our galaxy may have be shaped by ancient impacts.

    The study, titled “Milky Way Tomography with K and M Dwarf Stars: The Vertical Structure of the Galactic Disk“, recently appeared in the The Astrophysical Journal. Led by Deborah Ferguson, a 2016 UK graduate, the team consisted of Professor Susan Gardner – from the UK College of Arts and Sciences – and Brian Yanny, an astrophysicist from the Fermilab Center for Particle Astrophysics (FCPA).

    This study evolved from Ferguson’s senior thesis, which was overseen by Prof. Gardner. At the time, Ferguson sought to expand on previous research by Gardner and Yanny, which also sought to understand the presence of ripples in our galaxy’s stellar disk. For the sake of this new study, the team relied on data obtained by the Sloan Digital Sky Survey‘s (SDSS) 2.5m Telescope, located at the Apache Point Observatory in New Mexico.

    SDSS Telescope at Apache Point Observatory, NM, USA

    See the full article here .

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  • richardmitnick 3:38 pm on July 11, 2017 Permalink | Reply
    Tags: , , , , , , Extreme variability quasars, , SDSS   

    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 .

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    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 1:46 pm on July 5, 2017 Permalink | Reply
    Tags: , , , , , , , SDSS,   

    From U Cambridge: “Fastest stars in the Milky Way are ‘runaways’ from another galaxy” 

    U Cambridge bloc

    Cambridge University

    05 Jul 2017
    Sarah Collins
    sarah.collins@admin.cam.ac.uk

    1
    Artist’s impression of a runaway star. Credit: Amanda Smith, Institute of Astronomy.

    A group of astronomers have shown that the fastest-moving stars in our galaxy – which are travelling so fast that they can escape the Milky Way – are in fact runaways from a much smaller galaxy in orbit around our own. A group of astronomers have shown that the fastest-moving stars in our galaxy – which are travelling so fast that they can escape the Milky Way – are in fact runaways from a much smaller galaxy in orbit around our own.

    The researchers, from the University of Cambridge, used data from the Sloan Digital Sky Survey and computer simulations to demonstrate that these stellar sprinters originated in the Large Magellanic Cloud (LMC), a dwarf galaxy in orbit around the Milky Way.

    SDSS Telescope at Apache Point Observatory, NM, USA

    Large Magellanic Cloud. Adrian Pingstone December 2003

    These fast-moving stars, known as hypervelocity stars, were able to escape their original home when the explosion of one star in a binary system caused the other to fly off with such speed that it was able to escape the gravity of the LMC and get absorbed into the Milky Way. The results are published in the Monthly Notices of the Royal Astronomical Society, and will be presented today (5 July) at the National Astronomy Meeting in Hull.

    Astronomers first thought that the hypervelocity stars, which are large blue stars, may have been expelled from the centre of the Milky Way by a supermassive black hole. Other scenarios involving disintegrating dwarf galaxies or chaotic star clusters can also account for the speeds of these stars but all three mechanisms fail to explain why they are only found in a certain part of the sky.

    To date, roughly 20 hypervelocity stars have been observed, mostly in the northern hemisphere, although it’s possible that there are many more that can only be observed in the southern hemisphere.

    “Earlier explanations for the origin of hypervelocity stars did not satisfy me,” said Douglas Boubert, a PhD student at Cambridge’s Institute of Astronomy and the paper’s lead author. “The hypervelocity stars are mostly found in the Leo and Sextans constellations – we wondered why that is the case.”

    An alternative explanation to the origin of hypervelocity stars is that they are runaways from a binary system. In binary star systems, the closer the two stars are, the faster they orbit one another. If one star explodes as a supernova, it can break up the binary and the remaining star flies off at the speed it was orbiting. The escaping star is known as a runaway. Runaway stars originating in the Milky Way are not fast enough to be hypervelocity because blue stars can’t orbit close enough without the two stars merging. But a fast-moving galaxy could give rise to these speedy stars.

    The LMC is the largest and fastest of the dozens of dwarf galaxies in orbit around the Milky Way. It only has 10% of the mass of the Milky Way, and so the fastest runaways born in this dwarf galaxy can easily escape its gravity. The LMC flies around the Milky Way at 400 kilometres per second and, like a bullet fired from a moving train, the speed of these runaway stars is the velocity they were ejected at plus the velocity of the LMC. This is fast enough for them to be the hypervelocity stars.

    “These stars have just jumped from an express train – no wonder they’re fast,” said co-author Rob Izzard, a Rutherford fellow at the Institute of Astronomy. “This also explains their position in the sky, because the fastest runaways are ejected along the orbit of the LMC towards the constellations of Leo and Sextans.”
    Astronomers first thought that the hypervelocity stars, which are large blue stars, may have been expelled from the centre of the Milky Way by a supermassive black hole. Other scenarios involving disintegrating dwarf galaxies or chaotic star clusters can also account for the speeds of these stars but all three mechanisms fail to explain why they are only found in a certain part of the sky.

    To date, roughly 20 hypervelocity stars have been observed, mostly in the northern hemisphere, although it’s possible that there are many more that can only be observed in the southern hemisphere.

    “Earlier explanations for the origin of hypervelocity stars did not satisfy me,” said Douglas Boubert, a PhD student at Cambridge’s Institute of Astronomy and the paper’s lead author. “The hypervelocity stars are mostly found in the Leo and Sextans constellations – we wondered why that is the case.”

    An alternative explanation to the origin of hypervelocity stars is that they are runaways from a binary system. In binary star systems, the closer the two stars are, the faster they orbit one another. If one star explodes as a supernova, it can break up the binary and the remaining star flies off at the speed it was orbiting. The escaping star is known as a runaway. Runaway stars originating in the Milky Way are not fast enough to be hypervelocity because blue stars can’t orbit close enough without the two stars merging. But a fast-moving galaxy could give rise to these speedy stars.

    The LMC is the largest and fastest of the dozens of dwarf galaxies in orbit around the Milky Way. It only has 10% of the mass of the Milky Way, and so the fastest runaways born in this dwarf galaxy can easily escape its gravity. The LMC flies around the Milky Way at 400 kilometres per second and, like a bullet fired from a moving train, the speed of these runaway stars is the velocity they were ejected at plus the velocity of the LMC. This is fast enough for them to be the hypervelocity stars.

    “These stars have just jumped from an express train – no wonder they’re fast,” said co-author Rob Izzard, a Rutherford fellow at the Institute of Astronomy. “This also explains their position in the sky, because the fastest runaways are ejected along the orbit of the LMC towards the constellations of Leo and Sextans.”

    The researchers used a combination of data from the Sloan Digital Sky Survey and computer simulations to model how hypervelocity stars might escape the LMC and end up in the Milky Way. The researchers simulated the birth and death of stars in the LMC over the past two billion years, and noted down every runaway star. The orbit of the runaway stars after they were kicked out of the LMC was then followed in a second simulation that included the gravity of the LMC and the Milky Way. These simulations allow the researchers to predict where on the sky we would expect to find runaway stars from the LMC.

    “We are the first to simulate the ejection of runaway stars from the LMC – we predict that there are 10,000 runaways spread across the sky,” said Boubert. Half of the simulated stars which escape the LMC are fast enough to escape the gravity of the Milky Way, making them hypervelocity stars. If the previously known hypervelocity stars are runaway stars it would also explain their position in the sky.

    Massive blue stars end their lives by collapsing to a neutron star or black hole after hundreds of millions of years and runaway stars are no different. Most of the runaway stars in the simulation died ‘in flight’ after being kicked out of the LMC. The neutron stars and black holes that are left behind just continue on their way and so, along with the 10,000 runaway stars, the researchers also predict a million runaway neutron stars and black holes flying through the Milky Way.

    “We’ll know soon enough whether we’re right,” said Boubert. “The European Space Agency’s Gaia satellite will report data on billions of stars next year, and there should be a trail of hypervelocity stars across the sky between the Leo and Sextans constellations in the North and the LMC in the South.”

    ESA/GAIA satellite

    See the full article here .

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    U Cambridge Campus

    The University of Cambridge (abbreviated as Cantab in post-nominal letters) is a collegiate public research university in Cambridge, England. Founded in 1209, Cambridge is the second-oldest university in the English-speaking world and the world’s fourth-oldest surviving university. It grew out of an association of scholars who left the University of Oxford after a dispute with townsfolk. The two ancient universities share many common features and are often jointly referred to as “Oxbridge”.

    Cambridge is formed from a variety of institutions which include 31 constituent colleges and over 100 academic departments organised into six schools. The university occupies buildings throughout the town, many of which are of historical importance. The colleges are self-governing institutions founded as integral parts of the university. In the year ended 31 July 2014, the university had a total income of £1.51 billion, of which £371 million was from research grants and contracts. The central university and colleges have a combined endowment of around £4.9 billion, the largest of any university outside the United States. Cambridge is a member of many associations and forms part of the “golden triangle” of leading English universities and Cambridge University Health Partners, an academic health science centre. The university is closely linked with the development of the high-tech business cluster known as “Silicon Fen”.

     
  • richardmitnick 7:38 am on May 19, 2017 Permalink | Reply
    Tags: , , , Baryonic Oscillation Spectroscopic Survey [BOSS], , , , SDSS   

    From EPFL: “Astronomers make the largest map of the Universe yet” 

    EPFL bloc

    École Polytechnique Fédérale de Lausanne EPFL

    19.05.17
    Nik Papageorgiou

    1
    One of the SDSS telescopes at Apache Point Observatory in New Mexico (USA) ©SDSS

    Astronomers of the extended Baryonic Oscillation Spectroscopic Survey [BOSS], led by EPFL Professor Jean-Paul Kneib, used the Sloan telescope to create the first map of the Universe based entirely on quasars.

    BOSS Supercluster Baryon Oscillation Spectroscopic Survey (BOSS)

    Quasars are incredibly bright and distant points of light powered by supermassive black holes. As matter and energy fall into the black hole, they heat up to incredible temperatures and begin to glow with excessive brightness. By observing this cosmic glow, the scientists of the multi-institutional Sloan Digital Sky Survey (SDSS), which includes EPFL, have constructed the largest map of the distant Universe to-date. The work will be published in the Monthly Notices of the Royal Astronomical Society.

    Quasars are supermassive black holes at the centers of galaxies and they radiate huge amounts of electromagnetic energy. “Because quasars are so bright, we can see them all the way across the Universe,” says study co-leader Ashley Ross (Ohio State University). “That makes them the ideal objects to use to make the biggest map yet.”

    “These quasars are so far away that their light left them when the Universe was between 3 and 7 billion years old, long before the Earth even existed,” adds Gongbo Zhao from the National Astronomical Observatory of China, the study’s other co-leader.

    To construct the map, the scientists used the SDSS telescopes at New Mexico to measure accurate 3D positions for an unprecedented sample of over 147,000 quasars. This work took place during the first two years of the Extended Baryon Oscillation Spectroscopic Survey (eBOSS), one of the component research projects of SDSS led by Jean-Paul Kneib, Professor of Astrophysics at EPFL. The SDSS telescope observations gave the astronomers the quasars’ distances, which they then used to pinpoint the quasars’ positions in a 3D map.

    But the scientists didn’t stop there; they wanted to use to understand the expansion history of the Universe. For this they went a step further and used a clever technique that involves “baryon acoustic oscillations” (BAOs). These are the present-day imprint of sound waves that travelled through the early Universe, when it was much hotter and denser than it is now. But when the Universe was 380,000 years old, conditions changed suddenly and the sound waves became “frozen” in place, imprinted in the 3D structure of the Universe we see today.

    The process that produced these frozen BAOs is simple, which means that scientists can have a very good idea of what BAOs must have looked like in the early Universe. So when we look at the 3D structure of the Universe today, it contains these ancient BAOs, but massively stretched out by the expansion of the universe.

    The astronomers used the observed size of a BAO as “standard ruler” to measure distances in their 3D map, the way we can estimate the length of a football field by measuring the apparent angle of a meter rule on one side. “You have meters for small units of length, kilometres or miles for distances between cities, and we have the BAO scale for distances between galaxies and quasars in cosmology,” says Pauline Zarrouk, a PhD student at Irfu/CEA (University Paris-Saclay) who measured the projected BAO scale.

    Working backwards in time, the SDSS astronomers covered a range of time periods never observed before. The study measured the conditions when the Universe was just 3 to 7 billion years old, more than 2 billion years before the Earth formed.

    See the full article here .

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    EPFL campus

    EPFL is Europe’s most cosmopolitan technical university with students, professors and staff from over 120 nations. A dynamic environment, open to Switzerland and the world, EPFL is centered on its three missions: teaching, research and technology transfer. EPFL works together with an extensive network of partners including other universities and institutes of technology, developing and emerging countries, secondary schools and colleges, industry and economy, political circles and the general public, to bring about real impact for society.

     
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