Australian astronomers have contributed crucial data for the largest full-sky, three-dimensional survey of galaxies ever conducted, maps from which have just been published online.
The maps are the fruit of a decade of work by teams from the USA, Australia
and the UK. They show the ‘local’ cosmos out to a distance of
600 million light-years, quantifying the giant superclusters of galaxies
and the voids between them.
“This is the survey we’ve been waiting a decade for,”
said team member Dr Will Saunders of the Anglo-Australian Observatory.
Astronomers wanted a detailed map of how the galaxies are distributed, and
how they are moving around, to determine how the mysterious ‘dark
matter’ is distributed in the local universe. “Fortunately,
on large scales, dark matter is distributed almost the same way as luminous
matter, so we can use one to help unravel the other,” said the paper’s
lead author, Dr Pirin Erdogdu of Nottingham University.
The new survey, known as the 2MASS Redshift Survey (2MRS) has combined two
dimensional positions and colours from the Two Micron All Sky Survey (2MASS),
with redshifts of 25 000 galaxies over most of the sky, which give the approximate
distances to galaxies.
These redshifts were either measured specifically for the 2MRS or obtained
from a deep survey of the southern sky, the 6dF Galaxy Redshift Survey (6dFGS),
made with the UK Schmidt Telescope of the Anglo-Australian Observatory.
The great advantage of using the 2MASS data is that 2MASS was an infrared
survey, detecting heat rather than visible light. These near-infrared waves
are one of the few types of radiation that can penetrate the dust in our
Galaxy, allowing a clean all-sky map.
“The heat given off by galaxies reflects their real size,” said
Saunders. “So for the first time, we have a accurate and detailed
picture of the distribution of matter in the Universe around us.”
In order to map the dark matter probed by the survey, the team used a novel
technique borrowed from image processing. The method was partly developed
by Professor Ofer Lahav, a co-author of the paper and head of the astrophysics
group at University College London.
"These extraordinarily detailed maps of the Milky Way’s cosmic
neighbourhood provide a benchmark against which theories for the formation
of structure in the Universe can be tested,” said Professor Matthew
Colless, Director of the Anglo-Australian Observatory and leader of the
6dF Galaxy Survey.
“In the near future, the predicted motions derived from these maps
will be confronted with direct measurements of galaxies’ velocities
obtained by the 6dF Galaxy Survey, providing a new and stringent test of
cosmological models.”
This work is based the Two Micron All Sky Survey, which is a joint project
of the University of Massachusetts and the Infrared Processing and Analysis
Center / California Institute of Technology, funded by the National Aeronautics
and Space Administration and the U.S. National Science Foundation. This
research has also made use of the NASA / IPAC Extragalactic Database (NED)
which is operated by the Jet Propulsion Laboratory, California Institute
of Technology, under contract with the National Aeronautics and Space Administration,
and the SIMBAD database, operated at CDS, Strasbourg, France.
Researcher contacts
Prof. Matthew Colless, Anglo-Australian Observatory
Sydney, Australia
Tel: +61 2 9372-4812 (office)
director@aao.gov.au
Australian Eastern Standard Time is UT + 10 hours.
Dr Will Saunders, Anglo-Australian Observatory
Tel: +61-2-9372-4800
will@aao.gov.au
Australian Eastern Standard Time is UT + 10 hours.
Dr. Pirin Erdogdu (lead author)
University of Nottingham UK
Tel: +44 (0)115-846-8814
Mob: +44 (0)7896-343504
E-mail: pirin.erdogdu@nottingham.ac.uk
Images
1) A map of the mass density over the whole sky, for a thin shell 130 million light-years out from Earth. Red, green and blue indicate areas where mass is concentrated. The "Great Attractor" supercluster is made up of a group of galaxy clusters shown on the map: C2, Centaurus (CEN), Pavo-Indus-Telescopium (P-I-T), C8, Hydra (HYD), C3 and C4. Image credit: 2MRS team
www.aao.gov.au/press/13M_ly_out.jpg
2) A view of the sky towards the Great Attractor supercluster of galaxies. Photo: European Southern Observatory
1.1 MB file www.aao.gov.au/press/ESO_phot-46c-99-small.jpg
4.8 MB file www.aao.gov.au/press/ESO_phot-46c-99-mid.jpg
7.6 MB file www.aao.gov.au/press/ESO_phot-46c-99-large.jpg
Publication
The findings are presented in a paper entitled “Reconstructed Density
and Velocity Fields from the 2MASS Redshift Survey”, which has been
accepted for publication by the journal Monthly Notices of the Royal Astronomical
Society. This paper is available on the physics preprint server at
http://arxiv.org/PS_cache/astro-ph/pdf/0610/0610005.pdf