Rapid galaxy merging dominates universe's early history (Forwarded)

Public Affairs Office
University of Nottingham
Nottingham, U.K.

More information:

Dr Christopher J Conselice
+44 (0)115 951 5137
www.nottingham.ac.uk/~ppzcc1/

Emma Thorne
Media Relations Manager, Public Affairs Office
The University of Nottingham
+44 (0)115 951 5793

February 17, 2006

PA26/06

Rapid galaxy merging dominates universe's early history

A study by an academic at The University of Nottingham gives us the
first observational evidence for how massive galaxies in our universe
formed.

The implications of the study are vast and are being used by astronomers
to explain seemingly unrelated processes such as how massive black holes
and the universe's stars came to be.

The research, led by Dr Christopher J Conselice, of the University's
School of Physics and Astronomy, which is published in the February 20
edition of the Astrophysical Journal, uses the deepest images taken by
the Hubble Space Telescope to study galaxies when they were only two
billion years old. His team has found that the majority of the most
massive galaxies in the early universe are undergoing multiple and
spectacular mergers.

These mergers lead to the creation of new stars from colliding gas
clouds and likely feed and grow the masses of black holes lurking in the
centre of all galaxies.

The work is helping to definitively confirm what scientists have long
hoped for -- massive galaxies form when smaller galaxies merge together
-- a major and previously unconfirmed prediction of the cosmological
standard model.

"The results show us that the most massive galaxies we see in today's
universe, which are passive and old, were once undergoing rapid mergers
with each other, which it turns out is how they form," said Dr Conselice.

While distant galaxies have been studied for over a decade, it has until
now remained a mystery how they evolved into the galaxies we see today.

Young galaxies have very low masses and astronomers have long been
puzzled by how these systems turn into massive galaxies in the local
universe. The Conselice results demonstrate that a typical massive
galaxy in today's universe has undergone four to five mergers with other
galaxies to transform from these young low mass systems into the giant
galaxies.

These mergers are very rare today, with only about one per cent of
galaxies merging, while 10 billion years ago, nearly all massive
galaxies were undergoing mergers. An analysis technique developed by
Conselice for more than 10 years was used on the deepest images ever
taken of the universe to make these discoveries.

The results further show that massive galaxies did not form rapidly,
within a few million years after the Big Bang, or form gradually over an
extended period of time. In a surprising finding, almost all of this
merger activity occurs over a very short period of time, from the birth
of the universe to about six billion years ago.

Dr Conselice added: "Perhaps the most amazing thing about these results
is that massive galaxy formation is largely over when the universe is
half its current age. This means that all this merging activity was
somehow curtailed by an unknown process."

The research may hold clues about the formation of our own galaxy. The
Milky Way contains spiral arms, which are not thought to form through
the merger process. However, at the centre of our galaxy is a spherical
system of stars called a bulge -- a high-density region featuring many
old stars and a massive black hole -- which probably formed as a result
of these mergers.

The research could also help astronomers to see into the Milky Way's
future -- it is possible that our galaxy will itself merge with
Andromeda, our nearest neighbouring large galaxy in around a billion
years from now. This would see the destruction of the spiral disk that
surrounds the bulge and change dramatically the shape of our galaxy, as
well as significantly altering the positions of stars we see in the
night sky.

- Ends -

Notes to editors: The University of Nottingham undertakes world-changing
research and provides teaching of the highest quality. Ranked in the
THES World Top 100 Universities, its academics have won two Nobel Prizes
since 2003. An international institution, the University has campuses in
the United Kingdom, Malaysia and China.