Ref: http://physicsweb.org/articles/news/9/1/7/1
Galaxy surveys put cosmology on sound footing

12 January 2005

Two teams of astrophysicists have detected features in the large-scale
distribution of galaxies that can be traced back to fluctuations in the
cosmic microwave background. The variations in the cosmic background
are thought to result from quantum fluctuations in the very early
universe, shortly after the big bang. The results, which were presented
at the American Astronomical Society (AAS) meeting in San Diego
yesterday, provide further evidence for the standard big bang plus
inflation model of cosmology.

The cosmic microwave background (CMB) has a perfect black-body spectrum
with a temperature of 2.73 Kelvin. However, this temperature varies
very slightly at different points in the sky, corresponding to the
slight variations in the distribution of matter that existed some 380
000 years after the big bang.

When the power spectrum of the CMB is plotted as a function of angle it
contains a series of peaks that can be explained in terms of sound
waves travelling back and forth across the early universe. Two teams of
astrophysicists -- the Sloan Digital Sky Survey (SDSS) and the 2dF
Galaxy Redshift Survey (2dFGRS) -- have now shown that these
fluctuations in the CMB grew under the influence of gravity to produce
the pattern of galaxies and clusters of galaxy that we see today. Both
teams have detected a feature known as the "baryon acoustic peak".

The SDSS team, which uses the 2.5 m Sloan telescope in New Mexico,
mapped more than 46 000 galaxies over a volume of space around five
million light years in diameter. The SDSS team says that the results
agree perfectly with the standard model of cosmology in which 5% of the
universe is made of ordinary baryonic matter, with 25% dark matter and
70% dark energy. However, the nature of dark matter and dark energy
remains a mystery.

The 2dFGRS team have come to the same conclusion based on a smaller
survey with the 3.8 m Anglo-Australian telescope. "It is impressive
verification of the standard cosmological model that two groups with
independent data have both made significant detections of the
baryon-induced features in large-scale galaxy clustering," says Shaun
Cole of Durham University in the UK, who is the first author of the
2dFGRS paper (submitted to the Monthly Notices of the Royal
Astronomical Society).

"These baryon features are the genetic fingerprint of our universe,"
says Carlos Frenk, also of Durham. "They establish a direct
evolutionary link to the big bang. Finding them is a milestone in our
understanding of how the cosmos was formed."