[cdn-nucl-l] 3D Map of Universe Bolsters Case for Dark Energy and Dark Matter

["Adam McLean" <adam.mclean@utoronto.ca>]

Posted on the SDSS web page on October 27, 2003 at:
http://www.sdss.org/news/releases/20031028.powerspectrum.html

Adam

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3D Map of Universe Bolsters Case for Dark Energy and Dark Matter 
CONTACTS:
Prof. Max Tegmark, Univ. of Pennsylvania, 215-898-5942,
max@physics.upenn.edu
Prof. Michael Strauss, Princeton University, 609-258-3808,
strauss@astro.princeton.edu
Dr. Michael Blanton, New York University, 212-992-8791,
mb144@physics.nyu.edu
Gary S. Ruderman, Public Information Officer, The Sloan Digital Sky Survey:
312-320-4794 (cell), sdsspio@aol.com

October 27, 2003 -- Astronomers from the Sloan Digital Sky Survey (SDSS)
have made the most precise measurement to date of the cosmic clustering of
galaxies and dark matter, refining our understanding of the structure and
evolution of the Universe.

"From the outset of the project in the late 80's, one of our key goals has
been a precision measurement of how galaxies cluster under the influence of
gravity", explained Richard Kron, SDSS's director and a professor at The
University of Chicago.

SDSS Project spokesperson Michael Strauss from Princeton University and one
of the lead authors on the new study elaborated that: "This clustering
pattern encodes information about both invisible matter pulling on the
galaxies and about the seed fluctuations that emerged from the Big Bang."

The findings are described in two papers submitted to the Astrophysical
Journal and to the Physical review D; they can be found on the physics
preprint Web site, www.arXiv.org, on October 28.

MAPPING FLUCTUATIONS

The leading cosmological model invokes a rapid expansion of space known as
inflation that stretched microscopic quantum fluctuations in the fiery
aftermath of the Big Bang to enormous scales. After inflation ended, gravity
caused these seed fluctuations to grow into the galaxies and the galaxy
clustering patterns observed in the SDSS.

Images of these seed fluctuations were released from the Wilkinson Microwave
Anisotropy Probe (WMAP) in February, which measured the fluctuations in the
relic radiation from the early Universe.

"We have made the best three-dimensional map of the Universe to date,
mapping over 200,000 galaxies up to two billion light years away over six
percent of the sky", said another lead author of the study, Michael Blanton
from New York University. The gravitational clustering patterns in this map
reveal the makeup of the Universe from its gravitational effects and, by
combining their measurements with that from WMAP, the SDSS team measured the
cosmic matter to consist of 70 percent dark energy, 25 percent dark matter
and five percent ordinary matter.

  
The SDSS is two separate surveys in one: galaxies are identified in 2D
images (right), then have their distance determined from their spectrum to
create a 2 billion lightyears deep 3D map (left) where each galaxy is shown
as a single point, the color representing the luminosity - this shows only
those 66,976 our of 205,443 galaxies in the map that lie near the plane of
Earth's equator. (Click for high resolution jpg, version without lines.)  
They found that neutrinos couldn't be a major constituent of the dark
matter, putting among the strongest constraints to date on their mass.
Finally, the SDSS research found that the data are consistent with the
detailed predictions of the inflation model.

COSMIC CONFIRMATION

These numbers provide a powerful confirmation of those reported by the WMAP
team. The inclusion of the new SDSS findings helps to improve measurement
accuracy, more than halving the uncertainties from WMAP on the cosmic matter
density and on the Hubble parameter (the cosmic expansion rate). Moreover,
the new measurements agree well with the previous state-of-the-art results
that combined WMAP with the Anglo-Australian 2dF galaxy redshift survey.

"Different galaxies, different instruments, different people and different
analysis - but the results agree", says Max Tegmark from the University of
Pennsylvania, first author on the two papers. "Extraordinary claims require
extraordinary evidence", Tegmark says, "but we now have extraordinary
evidence for dark matter and dark energy and have to take them seriously no
matter how disturbing they seem."
  
The new SDSS results (black dots) are the most accurate measurements to date
of how the density of the Universe fluctuates from place to place on scales
of millions of lightyears. These and other cosmological measurements agree
with the theoretical prediction (blue curve) for a Universe composed of 5%
atoms, 25% dark matter and 70% dark energy. The larger the scales we average
over, the more uniform the Universe appears. (Click for high resolution jpg,
no frills version.)  

"The real challenge is now to figure what these mysterious substances
actually are", said another author, David Weinberg from Ohio State
University.

SDSS LARGE-SCALE UNDERTAKING

The SDSS is the most ambitious astronomical survey ever undertaken, with
more than 200 astronomers at 13 institutions around the world.

"The SDSS is really two surveys in one", explained Project Scientist James
Gunn of Princeton University. On the most pristine nights, the SDSS uses a
wide-field CCD camera (built by Gunn and his team at Princeton University
and Maki Sekiguchi of the Japan Participation Group) to take pictures of the
night sky in five broad wavebands with the goal of determining the position
and absolute brightness of more than 100 million celestial objects in
one-quarter of the entire sky. When completed, the camera was the largest
ever built for astronomical purposes, gathering data at the rate of 37
gigabytes per hour.

On nights with moonshine or mild cloud cover, the imaging camera is replaced
with a pair of spectrographs (built by Alan Uomoto and his team at The Johns
Hopkins University). They use optical fibers to obtain spectra (and thus
redshifts) of 608 objects at a time. Unlike traditional telescopes in which
nights are parceled out among many astronomers carrying out a range of
scientific programs, the special-purpose 2.5m SDSS telescope at Apache Point
Observatory in New Mexico is devoted solely to this survey, to operate every
clear night for five years.

The first public data release from the SDSS, called DR1, contained about 15
million galaxies, with redshift distance measurements for more than 100,000
of them. All measurements used in the findings reported here would be part
of the second data release, DR2, which will be made available to the
astronomical community in early 2004. 

Strauss said the SDSS is approaching the halfway point in its goal of
measuring one million galaxy and quasar redshifts.

"The real excitement here is that disparate lines of evidence from the
cosmic microwave background (CMB), large-scale structure and other
cosmological observations are all giving us a consistent picture of a
Universe dominated by dark energy and dark matter", said Kevork Abazajian of
the Fermi National Accelerator Laboratory and the Los Alamos National
Laboratory.


The authors are:

Max Tegmark, Department of Physics, University of Pennsylvania,
Philadelphia, PA 19101; Dept. of Physics, Massachusetts Institute of
Technology, Cambridge, MA 02139
Michael A. Strauss, Princeton University Observatory, Princeton, NJ 08544
Michael R. Blanton, Center for Cosmology and Particle Physics, Department of
Physics, New York University, 4 Washington Place, New York, NY 10003
Kevork Abazajian, Theoretical Division, MS B285, Los Alamos National
Laboratory, Los Alamos, New Mexico 87545
Scott Dodelson, Center for Cosmological Physics and Department of Astronomy
& Astrophysics, The University of Chicago, Chicago, IL 60637;
Fermi National Accelerator Laboratory, P.O. Box 500,
Batavia, IL 605107
Havard Sandvik, University of Pennsylvania
Xiaomin Wang, University of Pennsylvania
David H. Weinberg, Department of Astronomy, Ohio State University, Columbus,
OH 43210, USA
Idit Zehavi, The University of Chicago
Neta A. Bahcall, Princeton University
Fiona Hoyle, Department of Physics, Drexel University, Philadelphia, PA
19104, USA;
David Schlegel, Princeton University
Roman Scoccimarro, New York University
Michael S. Vogeley, Drexel University
Andreas Berlind, The University of Chicago
Tamas Budavari, Department of Physics and Astronomy, The Johns Hopkins
University, 3701 San Martin Drive, Baltimore, MD 21218
Andrew Connolly, University of Pittsburgh, Department of Physics and
Astronomy, 3941 O'Hara Street, Pittsburgh, PA 15260
Daniel J. Eisenstein, Department of Astronomy, University of Arizona,
Tucson, AZ 85721
Douglas Finkbeiner, Princeton University
Joshua A. Frieman, The University of Chicago; Fermi National Accelerator
Laboratory
James E. Gunn, Princeton University
Andrew J. S. Hamilton, JILA and Dept. of Astrophysical and Planetary
Sciences, U. Colorado, Boulder, CO 80309
Lam Hui, Fermi National Accelerator Laboratory
Bhuvnesh Jain, University of Pennsylvania
David Johnston, The University of Chicago; Fermi National Accelerator
Laboratory
Stephen Kent, Fermi National Accelerator Laboratory
Huan Lin, Fermi National Accelerator Laboratory
Reiko Nakajima, University of Pennsylvania
Robert C. Nichol, Department of Physics, 5000 Forbes Avenue, Carnegie Mellon
University, Pittsburgh, PA 15213
Adrian Pope, The Johns Hopkins University
Ryan Scranton, University of Pittsburgh
Uros Seljak, Princeton University
Ravi K. Sheth, University of Pittsburgh
Albert Stebbins, Fermi National Accelerator Laboratory
Alexander S. Szalay, The Johns Hopkins University
Istvan Szapudi, Institute for Astronomy, University of Hawaii, 2680 Woodlawn
Drive, Honolulu, HI 96822
Yongzhong Xu, Theoretical Division, MS B285, Los Alamos National Laboratory,
Los Alamos, New Mexico 87545
James Annis, Fermi National Accelerator Laboratory
J. Brinkmann, Apache Point Observatory, 2001 Apache Point Rd, Sunspot, NM
88349-0059
Scott Burles, Massachusetts Institute of Technology
Francisco J. Castander, Institut d'Estudis Espacials de Catalunya/CSIC, Gran
Capita 2-4, 08034 Barcelona, Spain
Istvan Csabai, The Johns Hopkins University
Jon Loveday, Sussex Astronomy Centre, University of Sussex, Falmer, Brighton
BN1 9QJ, UK
Mamoru Doi, Inst. for Cosmic Ray Research, Univ. of Tokyo, Kashiwa 277-8582,
Japan
Masataka Fukugita, University of Tokyo
Richard Gott III, Princeton University
Greg Hennessy, U.S. Naval Observatory, Flagstaff Station, Flagstaff, AZ
86002-1149
David W. Hogg, New York University
Zeljko Ivezic, Princeton University
Gillian R. Knapp, Princeton University
Don Q. Lamb, The University of Chicago
Brian C. Lee, Fermi National Accelerator Laboratory
Robert H. Lupton, Princeton University
Timothy A. McKay, Dept. of Physics, Univ. of Michigan, Ann Arbor, MI
48109-1120
Peter Kunszt, The Johns Hopkins University
Jeffrey A. Munn, U.S. Naval Observatory
Liam O'Connell, Sussex Astronomy Centre
Jeremiah P. Ostriker, Princeton University
John Peoples, Fermi National Accelerator Laboratory
Jeffrey R. Pier, U.S. Naval Observatory
Michael Richmond, Physics Dept., Rochester Inst. of Technology, 1 Lomb
Memorial Dr., Rochester, NY 14623
Constance Rockosi, The University of Chicago
Donald P. Schneider, Penn State
Christopher Stoughton, Fermi National Accelerator Laboratory
Douglas L. Tucker, Fermi National Accelerator Laboratory
Daniel E. Vanden Berk, University of Pittsburgh
Brian Yanny, Fermi National Accelerator Laboratory
Donald G. York, The University of Chicago, Enrico Fermi Institute,
University of Chicago, Chicago, IL 60637

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