Andrew Yee
April 4th 06, 11:22 PM
ROYAL ASTRONOMICAL SOCIETY PRESS INFORMATION NOTE
Issued by RAS Communications Officers:
Anita Heward
Tel: +44 (0)1483-420904
CONTACT
Dr. Ignacio Trujillo
School of Physics & Astronomy
University of Nottingham
University Park
Nottingham NG7 2RD
Tel: +44 (0)115-846-8819
TUESDAY, 4 APRIL 2006
RAS PN 06/27
THE UNIVERSE TRAPPED IN ITS OWN WEB
Astronomers from the University of Nottingham, UK, and the Instituto de
Astrofisica de Canarias (Spain), have found the first observational
evidence that galaxies are not randomly oriented.
Instead, they are aligned following a characteristic pattern dictated by
the large-scale structure of the invisible dark matter that surrounds
them.
This discovery confirms one of the fundamental aspects of galaxy formation
theory and implies a direct link between the global properties of the
Universe and the individual properties of galaxies.
Galaxy formation theories predicted such an effect, but its empirical
verification has remained elusive until now. The results of this work were
published the 1 April issue of Astrophysical Journal Letters.
Nowadays, matter is not distributed uniformly throughout space but is
instead arranged in an intricate "cosmic web" of filaments and walls
surrounding bubble-like voids. Regions with high galaxy concentrations are
known as galaxy clusters whereas low density regions are termed voids.
This inhomogeneous distribution of matter is called the "large-scale
distribution of the Universe." When the Universe is considered as whole,
this distribution has a similar appearance to a spideršs web or the neural
network of the brain. But it was not always like this.
After the Big Bang, when the Universe was much younger, matter was
distributed homogeneously. As the Universe was evolving, gravitational
pulls began to compress the matter in certain regions of space, forming
the large-scale structure that we currently observe.
According to these models and theories a direct consequence of this
process is that galaxies should be preferentially oriented perpendicularly
to the direction of the linear filaments.
Several observational studies have looked for a preferential spatial
orientation (or alignment) of galaxy rotation axes with respect to their
surrounding large-scale structures. However, none of them have been
successful, due to the difficulties associated with trying to characterise
the filaments.
The research conducted by the astrophysical group formed by Ignacio
Trujillo (University of Nottingham, UK), Conrado Carretero and Santiago G.
Patiri, (both from the Instituto de Astrofisica de Canarias, Spain) has
been able to measure this effect, confirming theoretical predictions.
To achieve this goal, they used a new technique based on the analysis of
the huge voids that are found in the large-scale structure of the
Universe. These voids have been detected by searching for large regions of
space depleted of bright galaxies.
In addition, they took advantage of information provided by the two
largest sky surveys yet undertaken: the Sloan Digital Sky Survey and the
Two Degree Field Survey. These surveys contain positional information for
more than half a million galaxies located within a distance of one billion
light-years of the Earth.
Other parameters provided by the surveys, such as the position angle and
the ellipticity of the objects, were used to estimate the orientation of
the disk galaxies.
"We found that there is an excess of disk galaxies that are highly
inclined relative to the plane defined by the large-scale structure
surrounding them," explained Dr. Trujillo. "Their rotation axes are mainly
oriented in the direction of the filaments.
"Our work provides important confirmation of the tidal torque theory which
explains how galaxies have acquired their current spin," said Trujillo.
"The spin of the galaxies is believed to be intrinsically linked to their
morphological shapes. So, this work is a step forward on our understanding
of how galaxies have reached their current shapes."
Dr. Ignacio Trujillo has a research assistant position, funded by PPARC,
in the School of Physics and Astronomy at the University of Nottingham.
An abstract of the paper is available on the web at:
http://xxx.lanl.gov/abs/astro-ph/0511680
IMAGES
A movie and images are available at:
http://www.iac.es/gabinete/noticias/2006/univ-gescala/imagen.html
Issued by RAS Communications Officers:
Anita Heward
Tel: +44 (0)1483-420904
CONTACT
Dr. Ignacio Trujillo
School of Physics & Astronomy
University of Nottingham
University Park
Nottingham NG7 2RD
Tel: +44 (0)115-846-8819
TUESDAY, 4 APRIL 2006
RAS PN 06/27
THE UNIVERSE TRAPPED IN ITS OWN WEB
Astronomers from the University of Nottingham, UK, and the Instituto de
Astrofisica de Canarias (Spain), have found the first observational
evidence that galaxies are not randomly oriented.
Instead, they are aligned following a characteristic pattern dictated by
the large-scale structure of the invisible dark matter that surrounds
them.
This discovery confirms one of the fundamental aspects of galaxy formation
theory and implies a direct link between the global properties of the
Universe and the individual properties of galaxies.
Galaxy formation theories predicted such an effect, but its empirical
verification has remained elusive until now. The results of this work were
published the 1 April issue of Astrophysical Journal Letters.
Nowadays, matter is not distributed uniformly throughout space but is
instead arranged in an intricate "cosmic web" of filaments and walls
surrounding bubble-like voids. Regions with high galaxy concentrations are
known as galaxy clusters whereas low density regions are termed voids.
This inhomogeneous distribution of matter is called the "large-scale
distribution of the Universe." When the Universe is considered as whole,
this distribution has a similar appearance to a spideršs web or the neural
network of the brain. But it was not always like this.
After the Big Bang, when the Universe was much younger, matter was
distributed homogeneously. As the Universe was evolving, gravitational
pulls began to compress the matter in certain regions of space, forming
the large-scale structure that we currently observe.
According to these models and theories a direct consequence of this
process is that galaxies should be preferentially oriented perpendicularly
to the direction of the linear filaments.
Several observational studies have looked for a preferential spatial
orientation (or alignment) of galaxy rotation axes with respect to their
surrounding large-scale structures. However, none of them have been
successful, due to the difficulties associated with trying to characterise
the filaments.
The research conducted by the astrophysical group formed by Ignacio
Trujillo (University of Nottingham, UK), Conrado Carretero and Santiago G.
Patiri, (both from the Instituto de Astrofisica de Canarias, Spain) has
been able to measure this effect, confirming theoretical predictions.
To achieve this goal, they used a new technique based on the analysis of
the huge voids that are found in the large-scale structure of the
Universe. These voids have been detected by searching for large regions of
space depleted of bright galaxies.
In addition, they took advantage of information provided by the two
largest sky surveys yet undertaken: the Sloan Digital Sky Survey and the
Two Degree Field Survey. These surveys contain positional information for
more than half a million galaxies located within a distance of one billion
light-years of the Earth.
Other parameters provided by the surveys, such as the position angle and
the ellipticity of the objects, were used to estimate the orientation of
the disk galaxies.
"We found that there is an excess of disk galaxies that are highly
inclined relative to the plane defined by the large-scale structure
surrounding them," explained Dr. Trujillo. "Their rotation axes are mainly
oriented in the direction of the filaments.
"Our work provides important confirmation of the tidal torque theory which
explains how galaxies have acquired their current spin," said Trujillo.
"The spin of the galaxies is believed to be intrinsically linked to their
morphological shapes. So, this work is a step forward on our understanding
of how galaxies have reached their current shapes."
Dr. Ignacio Trujillo has a research assistant position, funded by PPARC,
in the School of Physics and Astronomy at the University of Nottingham.
An abstract of the paper is available on the web at:
http://xxx.lanl.gov/abs/astro-ph/0511680
IMAGES
A movie and images are available at:
http://www.iac.es/gabinete/noticias/2006/univ-gescala/imagen.html