Fundamental Property of Galaxies Discovered at W. M. Keck Observatory(Forwarded)

W. M. Keck Observatory

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March 6th, 2007

Fundamental Property of Galaxies Discovered at W. M. Keck Observatory

Kamuela -- A new study using data collected by the W. M. Keck Observatory
in Hawaii has revealed that certain fundamental properties of galaxies
have actually changed very little over the last 8 billion years, nearly
half of the age of the universe.

According to the research, the relationship between a galaxy's mass and a
new speed indicator that measures movement of its stars and gas remains
the same for all forms of galaxies, from spirals like our own Milky Way,
to elliptical galaxies, and even the so-called "train wrecks" left over by
galactic mergers.

"Surprisingly, if you use this new speed indicator to measure the motions
of stars and gas in a galaxy, you can predict the mass in stars the galaxy
has with pretty high accuracy," said Susan Kassin, a post-doctoral
researcher at the University of California, Santa Cruz and lead author of
the study.

Galaxies like our Milky Way are made up of billions of stars formed into a
spiral disk along with some gas. Like a spinning pinwheel, our galaxy also
spins, but at a speed of a few hundred kilometers per second.

It's known that half of the age of the universe ago, many galaxies look
more disheveled, as they are assembled through galaxy collisions and
accretion of new gas and stars. According to the research, disheveled
galaxies and the remnants of galaxy collisions have mixed-up velocities in
addition to some orderly rotation. Furthermore, the research found that
when all these velocities are totaled up, the total amount of motion was
found to be similar to that of more well behaved galaxies. "This suggests
that the mixed-up velocities may settle down to orderly rotation over time
as the universe ages," said Ben Weiner, a researcher at Steward
Observatory at the University of Arizona and a co-author of the study.

There are three main types of galaxies in the universe: spiral or
disk-like galaxies like our own Milky Way, elliptical or cloud-like
galaxies, and the remnants of galaxy collisions. It was previously known
that when it comes to spiral galaxies, the more massive the galaxy, the
faster its stars and gas rotate. The relation between the mass in stars of
spiral galaxies and the rotation speed of their stars and gas is known as
the Tully-Fisher relation. When it comes to elliptical galaxies, the more
massive a galaxy is, the faster the random motions of its stars. This
relation is known as the Faber-Jackson relation. The latest research went
a step further; discovering a new relation between how massive a galaxy is
and a new speed indicator that takes into account both rotation velocity
and random or disordered motion. This new relation applies to spiral,
elliptical, and other types of galaxies, like disheveled galaxies or the
remnants of galaxy collisions, and has remained essentially the same over
the past 8 billion years -- roughly half the age of the universe.

Kassin, Weiner, and the other researchers were able to bring together both
the Tully-Fisher and Faber-Jackson relations -- and include "disturbed" or
train-wreck galaxies which previously didn't figure in either -- by using
a new speed indicator, a number which when applied to galaxies, allows
astronomers to better mathematically define the movement of stars.

"This relation holds for all the galaxies, no matter what they look like,"
Kassin said. "It ties together the Faber-Jackson relation with the
Tully-Fisher relation and works for all kinds of odd-ball galaxies that
are more common in the early universe."

According to Sandra Faber, co-author of the study and one of the namesakes
of the Faber-Jackson relation which she helped develop in 1976, the
research is believed to reflect a fundamental property of the universe.

"Both of these relations were imprinted by the nature of fluctuations that
made galaxies in the first place," she said.

The recent study involved 544 distant galaxies of various types, which
according to Kassin makes this the largest study to date of the speed and
movement of distant galaxies' stars and other matter. The galaxies studied
ranged in redshift from 0.1 to 1.2, which means their light was emitted
between 2 billion and 8 billion years ago. Redshift is a way of gauging
the distance of an object by measuring how much of the wavelength of its
light has shifted toward the redder regions of the spectrum due to
galaxies moving away from us because of the expansion of the universe. It
is similar to the Doppler Effect which involves changes in sound from an
object moving away from oneself.

Kassin said the DEIMOS spectrograph at Keck II, one of two 10-meter
telescopes the observatory operates on the summit of Mauna Kea, was key to
obtaining the amount of data necessary for the study. "Without it, we
wouldn't have been able to have anything close to this large of a sample,"
she said. Additional data came from the Hubble Space Telescope and the
Canada-France-Hawaii Telescope, which is also located atop Mauna Kea. The
results of the research have been presented in a study to be published in
a special issue of "Astrophysical Journal Letters" devoted to the initial
results of a far-reaching study of galaxies know as AEGIS, for
All-wavelength Extended Groth Strip International Survey. AEGIS involves
nearly 100 scientists from 16 institutions in Europe, North America, and
Asia studying a certain area of the sky using a variety of wavelengths
ranging from X-rays to radio and including ultraviolet and visible light.
For more information see the Web site at
http://aegis.ucolick.org

Funding for this research was provided by the National Science Foundation
and NASA. The study was also co-authored by David Koo, Justin Harker, Anne
Metevier, Andrew Phillips, Jürg Diemand, Nicholas Konidaris, Kai Noeske
and of UCSC; Jennifer Lotz of the National Optical Astronomical
Observatories; Kevin Bundy of the University of Toronto; Michael Cooper
and Darren Croton of the University of California at Berkeley and
Christopher Willmer of Steward Observatory at the University of Arizona.

The W. M. Keck Observatory is operated by the California Association for
Research in Astronomy (CARA), a non-profit 501 (c) (3) corporation whose
governing board consists of directors from the California Institute of
Technology and the University of California. In addition, the National
Aeronautics and Space Administration and the W. M. Keck Foundation each
have liaisons to the board. Construction of the twin Keck telescopes and
domes was made possible with generous grants totaling more than $140
million from the W. M. Keck Foundation in Los Angeles.