Two Milky Way Companion Galaxies Discovered
The Constellation Bootes
The figures are created from SDSS-II images. Each star in the photometric database is assigned a color and plotted as to the star's brightness. These images are filtered by selecting stars whose colors and magnitudes are characteristic of the stars in each galaxy. (Filtered images on the right.) Credit: Vasily Belokurov, Cambridge University, The Sloan Digital Sky Survey-II collaboration
A team of scientists, which includes a Penn State astronomer, is announcing today the discovery of two faint galaxies that are companions of the Milky Way. The study, lead by Daniel Zucker of Cambridge University, used images produced by the Sloan Digital Sky Survey (SDSS) to identify the galaxies, which are located at distances of 200,000 and 640,000 light years from the sun. "If our understanding of the formation of galaxies is correct, the Milky Way should have a large number of such satellites," stated Penn State Professor of Astronomy and Astrophysics Donald Schneider, a coauthor of the investigation. "Unfortunately these dwarf galaxies are so faint that they are difficult to detect, and it is possible that the two discoveries, combined with the ten previously known dwarf galaxies, may be just the tip of the iceberg."
Schneider is the Chairman of the SDSS Quasar Science Group and the SDSS Scientific Publications Coordinator. "One particularly interesting aspect of this discovery is how unexpected it was," said Schneider. "The SDSS was designed to investigate the large-scale structure of the universe by finding objects billions of light years from the sun. It is amazing that the versatility of the SDSS allowed us to gain insight into what is, astronomically speaking, in our back yard."
The following text, released by the Sloan Digital Sky Survey, contains more information. Schneider can be reached for comment at 814-863-9554 or dps@astro.psu.edu, or via Barbara Kennedy (PIO) at 814-863-4682 or science@psu.edu.
NEWS FROM THE SLOAN DIGITAL SKY SURVEY: NEW MILKY WAY COMPANIONS FOUND -- SDSS-II is first to view two, very dim dwarf galaxies
The Constellation Canes Venatici
The figures are created from SDSS-II images. Each star in the photometric database is assigned a color and plotted as to the star's brightness. These images are filtered by selecting stars whose colors and magnitudes are characteristic of the stars in each galaxy. (Filtered images on the right.) Credit: Vasily Belokurov, Cambridge University, The Sloan Digital Sky Survey-II collaboration
(8 May 2006) -- The Sloan Digital Sky Survey (SDSS-II) announced today discoveries of two new, very faint companion galaxies to the Milky Way. The first was found in the direction of the constellation Canes Venatici (the Hunting Dog) by SDSS-II researcher Daniel Zucker at Cambridge University (UK). His colleague Vasily Belokurov discovered the second in the constellation Bootes (the Herdsman).
"I was poring over the survey's map of distant stars in the Northern Galactic sky - -what we call a Field of Streams -- and noticed an overdensity in Canes Venatici," Zucker explained. "Looking further, it proved to be a previously unknown dwarf galaxy. It's about 640,000 light years (200 kiloparsecs) from the Sun. This makes it one of the most remote of the Milky Way's companion galaxies."
Zucker E-mailed Belokurov with the news, and, just as discoveries often build upon one another, Belokurov excitedly E-mailed back a few hours later with the discovery of a new, even fainter dwarf galaxy. The new galaxy in Bootes, which Belokurov called 'Boo,' shows a distorted structure that suggests it is being disrupted by the Milky Way's gravitational tides. "Something really bashed Boo about," said Belokurov.
Although the dwarf galaxies are in our own cosmic backyard, they are hard to discover because they are so dim. In fact, the new galaxy in Bootes is the faintest galaxy so far discovered, with a total luminosity of only about 100,000 Suns. But because of its distance (640,000 light years) it appears almost invisible to most telescopes. The previous dimness record holder was discovered last year in Ursa Major using SDSS-II data.
New galactic neighbors are exciting in their own right, but the stakes in searches for ultra-faint dwarfs are especially high because of a long-standing conflict between theory and observations. The leading theory of galaxy formation predicts that hundreds of clumps of "cold dark matter" should be orbiting the Milky Way, each one massive enough in principle to host a visible dwarf galaxy. But only about ten dwarf companions have been found to date.
One possibility is that the galaxies in the smaller dark matter clumps are too faint to have appeared in previous searches, but might be detectable in deep surveys like SDSS-II. "It's like panning for gold. Our view of the sky is enormous, and we're looking for very small clumps of stars," explained Cambridge University astronomer Wyn Evans , a member of the SDSS-II research team. Added collaborator Mark Wilkinson, " Finding and studying these small galaxies is really important. From their structure and their motions, we can learn about the properties of dark matter, as well as measure the mass and the gravity field of the Milky Way."
The new discoveries are part of the SEGUE project (Sloan Extension for Galactic Understanding and Exploration), one of the three component surveys of SDSS-II. SEGUE will probe the structure and stellar make-up of the Milky Way Galaxy in unprecedented detail. "I'm confident there are more dwarf galaxies out there and SEGUE will find them,” said Heidi Newberg of Rensselaer Polytechnic Institute, co-chair of SEGUE.
(A full list of authors can be found at www.sdss.org)
ABOUT THE SLOAN DIGITAL SKY SURVEY( www.sdss.org)
The Sloan Digital Sky Survey (SDSS-II) addresses fascinating, fundamental questions about the universe. With the survey, astronomers will be able to see the large-scale patterns of galactic sheets and voids in the universe. Scientists have varying ideas about the evolution of the universe, and different patterns of large-scale structure point to different theories of how the universe evolved. The Sloan Digital Sky Survey will tell us which theories are right -- or whether we have to come up with entirely new ideas.
Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation , the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSS Web Site is www.sdss.org/.
The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions: The American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, Cambridge University, Case Western Reserve University, University of Chicago, Drexel University, The Fermi National Accelerator Laboratory, the Institute for Advanced Study, the Japan Participation Group, The Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory and the University of Washington.
CONTACTS AT SDSS
Daniel Zucker, Cambridge University, zucker@ast.cam.ac.uk, 01223 737529
Vasily Belokurov, Cambridge University, vasily@ast.cam.ac.uk, 01223 337515
Wyn Evans, Cambridge University, nwe@ast.cam.ac.uk, 01223 765847
David Weinberg, Scientific Spokesperson, The Sloan Digital Sky Survey, dhw@astronomy.ohio-state.edu, 614-292-6543
Gary S. Ruderman, Public Information Officer, The Sloan Digital Sky Survey, sdsspio@aol.com, 312-320-4794
CONTACTS AT PENN STATE:
Donald Schneider, 814-863-9554, dps@astro.psu.edu
Barbara Kennedy (PIO), 814-863-4682 science@psu.edu