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5 October 2006

For immediate use


Largest-ever all-sky 3D map of galaxies

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