Distant quasars live in massive dark matter halos (Forwarded)

Sloan Digital Sky Survey

Contacts:

Yue Shen
Princeton University
609-258-8057

Michael Strauss
Princeton University
609-258-3808

David Weinberg
Scientific Spokesperson, Sloan Digital Sky Survey
614-406-6243

Gary S. Ruderman
Public Information Officer, Sloan Digital Sky Survey
312-320-4794

February 9, 2007

Distant quasars live in massive dark matter halos

Using a map of more than 4,000 luminous quasars in the distant universe,
scientists from the Sloan Digital Sky Survey (SDSS-II) have shown that
these brilliant beacons are strongly clumped, with huge quasar
superclusters separated by vast stretches of empty space. The strong
clustering shows that the quasars lie within massive concentrations of
dark matter.

"Previous maps showed that more nearby quasars cluster like 'normal'
galaxies," explained Princeton University graduate student Yue Shen, who
led the study. "But the clustering in our map is ten times stronger, the
difference between a high contrast photograph and a washed-out Xerox."

Quasars are glowing, ultraluminous concentrations of swirling gas falling
into supermassive black holes at the centers of otherwise ordinary
galaxies. Their great luminosities allow them to be seen at enormous
distances, and since light travels at a finite speed, quasar maps provide
a glimpse of structure when the universe was a small fraction of its
current age.

"Quasars lie in galaxies, which lie in extended halos of invisible dark
matter," said Princeton University astronomer Michael Strauss, a member of
Shen's team. "In a typical galaxy, the dark matter outweighs the stars by
10 to one."

"We can't observe the dark halos directly," Strauss explained, "but we
know from theoretical calculations how they should cluster with one
another. By measuring the clustering of the quasars, we can infer the
masses of the 'halos' in which they live."

"We've shown that the brightest quasars, powered by the biggest black
holes, lie in the most massive halos of the early universe, several
trillion times the mass of the sun," added Shen, "This is roughly what
theories predict."

The luminous distant quasars -- powered by black holes up to a billion
times the mass of the sun -- are extremely rare, with average separations
of 200 million light years or more. Before the SDSS, only a few hundred
quasars had been discovered beyond 11 billion light years, the minimum
distance of Shen's sample,

"The SDSS made this possible by imaging a large area of sky to great
depth, then following up the candidates to show which were true quasars,"
said team member Gordon Richards of Drexel University. "Until you have a
few thousand objects in your map, you can't make this measurement."

Because gravity pulls dark matter into denser structures over time, the
clustering of dark matter in the early universe was much weaker than it is
today. Richards explained the strong clustering of the brightest quasars
as analogous to that of the highest mountain peaks on earth. "Most of them
lie in the Himalayas, the Andes, the Rockies or the Alps."

"There's a whole low-altitude landscape of galaxies and dark matter," said
Richards, "but when you look for the brightest quasars you pick out just
the snowcapped mountain ranges."

The new measurements shed light on the early growth of supermassive black
holes, according to theorist Avi Loeb of Harvard University, who is not a
member of the SDSS-II team.

"The existence of bright quasars at early cosmic times is one of the
unsolved mysteries of cosmology," Loeb said. "How did black holes grow to
a billion times the mass of the sun when the universe was only a tenth of
its current age? The SDSS measurements will help us answer this question."

The results are described in the paper "Clustering of High Redshift (Z
2.9) Quasars from the Sloan Digital Sky Survey," which was posted to the
astro-ph archive today [http://arxiv.org/abs/astro-ph/0702214]. It has
been accepted for publication in The Astronomical Journal.

Authors:

Yue Shen, Princeton University
Michael A. Strauss, Princeton University
Masamune Oguri, KIPAC/Stanford
Joseph F. Hennawi, U.C. Berkeley
Xiaohui Fan, University of Arizona
Gordon T. Richards, Drexel University
Patrick B. Hall, York University
James E. Gunn, Princeton University
Donald P. Schneider, Pennsylvania State University
Alexander S. Szalay, Johns Hopkins University
Anirudda R. Thakar, Johns Hopkins University
Daniel E. Vanden Berk, Pennsylvania State University
Scott F. Anderson, University of Washington
Neta A. Bahcall, Princeton University
Andrew J. Connolly, University of Pittsburgh
Gillian R. Knapp, Princeton University

IMAGE CAPTION:
[http://www.sdss.org/news/releases/20..._enlarge.html]
The illustration above shows the distribution of dark matter, massive
halos, and luminous quasars in a simulation of the early universe, shown
1.6 billion years after the Big Bang. Gray-colored filamentary structure
shows the distribution of "invisible" dark matter. Small white circles
mark concentrated "halos" of dark matter more massive than 3 trillion
times the mass of the sun. Larger blue circles mark the most massive
halos, more than 7 trillion times of the sun, which host the most luminous
quasars. The strong clustering of the quasars in the SDSS sample
demonstrates that they reside in these rare, very massive halos.

This box is 360 million light years across.

(Credit: Paul Bode and Yue Shen, Princeton University)