3D map of Universe bolsters case for dark energy and dark matter
Here are some resources on the new SDSS measurements of the galaxy power
spectrum and cosmological parameters, including the press release
and print-quality images.
If you are a scientist, you'll want to click
here for the papers, downloadable data
and technical figures.
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.
high resolution jpg,
version without lines.)
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.
high resolution jpg,
no frills version.)
The following release was issued by the Sloan Digital sky Survey
press office in Chicago, Illinois, on October 22, 2003
3D Map of Universe Bolsters Case for Dark Energy and Dark Matter
(EMBARGOED UNTIL 8 PM EASTERN TIME, MONDAY OCTOBER 27, 2003)
- Prof. Max Tegmark, Univ. of Pennsylvania
- Prof. Michael Strauss, Princeton University
- Dr. Michael Blanton, New York University
- Gary S. Ruderman, Public Information Officer,
The Sloan Digital Sky Survey:
312-320-4794 (cell), firstname.lastname@example.org
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.
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
They found that neutrinos couldn't be a major constituent of the dark matter,
putting 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.
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 scientists and
different analyses - but the results agree beautifully", says Max
Tegmark from the University of Pennsylvania, first author on the two
papers. "Carl Sagan was fond of saying that 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 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
redhsifts) 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.
(A complete list of authors and institutions can be found at www.sdss.org)
ABOUT THE SLOAN DIGITAL SKY SURVEY
The Sloan Digital Sky Survey (www.sdss.org)
is a joint project of The
University of Chicago, Fermilab, the Institute for Advanced Study, the Japan
Participation Group, The Johns Hopkins University, the Los Alamos National
Laboratory, the Max-Planck-Institute for Astronomy (MPIA), the Max-Planck-
Institute for Astrophysics (MPA), New Mexico State University, University of
Pittsburgh, Princeton University, the United States Naval Observatory, and
the University of Washington.
Funding for the project has been provided by the Alfred P. Sloan Foundation,
the Participating Institutions, the National Aeronautics and Space
Administration, the National Science Foundation, the U.S. Department of
Energy, the Japanese Monbukagakusho, and the Max Planck Society.
The press release above refers to two papers appearing simultaneously
on astro-ph in the mailing of Tuesday October 28, 2003:
Here are the abstracts of these two papers:
- The 3D power spectrum of galaxies from the SDSS,
Max Tegmark, Michael R. Blanton, Michael A. Strauss, Fiona S. Hoyle, David Schlegel, Roman Scoccimarro, Michael S. Vogeley, David H. Weinberg, Idit Zehavi Andreas Berlind, Tamas
Budavari, Andrew Connolly, Scott Dodelson, Daniel J. Eisenstein, Joshua A. Frieman, James E. Gunn, Lam Hui, Bhuvnesh Jain, David Johnston, Stephen Kent, Huan Lin, Reiko
Nakajima, Robert C. Nichol, Adrian Pope, Ryan Scranton, Uros Seljak, Ravi K. Sheth, Albert Stebbins, Alexander S. Szalay, Istvan Szapudi, Yongzhong Xu, James Annis, Neta A.
Bahcall, J. Brinkmann, Istvan Csabai, Jon Loveday, Mamoru Doi, Masataka Fukugita, Richard Gott III, Greg Hennessy, David Hogg, Zeljko Ivezic, Gillian R. Knapp, Don Q. Lamb, Brian C. Lee, Robert
H. Lupton. Timothy A. McKay. Peter Kunszt. Jeffrey A. Munn. Liam O'Connell. Jeremiah P. Ostriker, John Peoples, Jeffrey R. Pier, Michael Richmond, Constance Rockosi,
Christopher Stoughton, Douglas L. Tucker, Brian Yanny and Donald G. York, for the SDSS Collaboration,
submitted to the Astrophysical Journal (40 ApJ pages, 40 figures, 3 tables)
Download: pdf, ps
- Cosmological parameters from SDSS and WMAP,
Max Tegmark, Michael Strauss, Michael R. Blanton, Kev Abazajian, Scott Dodelson, Havard Sandvik, Xiaomin
Wang, David H. Weinberg, Idit Zehavi, Neta A. Bahcall, Fiona Hoyle, David Schlegel, Roman Scoccimarro,
Michael S. Vogeley, Andreas Berlind, Tamas Budavari, Andrew Connolly, Daniel J. Eisenstein, Douglas
Finkbeiner, Joshua A. Frieman, James E. Gunn, Lam Hui, Bhuvnesh Jain, David Johnston,
Stephen Kent, Huan Lin, Reiko Nakajima, Robert C. Nichol, Adrian Pope, Ryan Scranton, Uros Seljak, Ravi K.
Sheth, Albert Stebbins, Alexander S. Szalay, Istvan Szapudi, Yongzhong Xu, James Annis, J. Brinkmann, Scott
Burles, Francisco J. Castander, Istvan Csabai, Jon Loveday, Mamoru Doi, Masataka Fukugita, Greg Hennessy,
David W. Hogg, Zeljko Ivezic, Gillian R. Knapp, Don Q. Lamb, Brian C. Lee, Robert H. Lupton, Timothy A.
McKay, Peter Kunszt, Jeffrey A. Munn, Liam O'Connell, Jeremiah P. Ostriker, John Peoples, Jeffrey R. Pier,
Michael Richmond, Constance Rockosi, Donald P. Schneider, Christopher Stoughton, Douglas L. Tucker, Daniel E.
Vanden Berk, Brian Yanny and Donald G. York,
submitted to Physical Review D (26 PRD pages, 18 figures, 8 tables)
Download: pdf, ps
The 3D Power Spectrum of Galaxies from the SDSS
We measure the large-scale real-space power spectrum P(k) using a sample of 205,443 galaxies
from the Sloan Digital Sky Survey, covering 2417 effective square degrees with mean redshift
We employ a matrix-based method using pseudo-Karhunen-Loeve eigenmodes,
uncorrelated minimum-variance measurements in 22 k-bands of
both the clustering power and its anisotropy due to redshift-space distortions,
with narrow and well-behaved window functions in the range
0.02h/Mpc < k < 0.3h/Mpc.
We pay particular attention to modeling, quantifying and correcting for
potential systematic errors,
nonlinear redshift distortions and
the artificial red-tilt caused by
luminosity-dependent bias. Our results are robust to omitting angular and
radial density fluctuations and are consistent between different
parts of the sky.
Our final result is a measurement of the real-space matter power spectrum P(k)
up to an unknown overall multiplicative bias factor.
Our calculations suggest that this bias factor
is independent of scale to better than a few percent for k < 0.1h/Mpc,
thereby making our results useful for precision measurements of
cosmological parameters in conjunction with data from other experiments such as
the WMAP satellite. The power spectrum is not well-characterized by a
single power law, but unambiguously shows curvature.
As a simple characterization of the data,
our measurements are well fit by a flat scale-invariant adiabatic cosmological model with
h Omega_m = 0.213 +/- 0.023
and sigma_8 = 0.89 +/- 0.02 for L* galaxies,
when fixing the baryon fraction
and the Hubble parameter h=0.72.
Cosmological parameters from SDSS and WMAP
We measure cosmological parameters using the three-dimensional power spectrum P(k)
from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in combination with WMAP and other data.
Our results are consistent with a
``vanilla'' flat adiabatic Lambda-CDM model without
tilt (n=1), running tilt, tensor modes or massive neutrinos.
Adding SDSS information more than halves the WMAP-only error bars on some parameters,
tightening 1 sigma constraints on the Hubble parameter from
on the matter density from
Omega_m~0.30+/-0.04 (1 sigma)
and on neutrino masses from <11 eV to <0.6 eV (95%).
SDSS helps even more when dropping prior assumptions about curvature, neutrinos, tensor modes
and the equation of state.
Our results are in
substantial agreement with the joint analysis of WMAP and the 2dF
Galaxy Redshift Survey, which is an impressive consistency check with
independent redshift survey data and analysis techniques.
In this paper,
we place particular emphasis on clarifying the physical origin of the constraints,
i.e., what we do and do not know when using different data sets and
For instance, dropping the assumption that space is perfectly flat,
the WMAP-only constraint on
the measured age of the Universe tightens from
t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data.
Including tensors, running tilt, neutrino mass and equation of state in
the list of free parameters, many constraints are still quite weak,
but future cosmological measurements from SDSS and other sources
should allow these to be substantially tightened.
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