Astronomers peer into the dark
Current models of the Universe predict that galaxies reside in large clumps of dark matter, commonly referred to as dark matter halos. Unlike individual galaxies, galaxy groups provide a unique environment in which to study the properties of this elusive material. Understanding the 20% of the cosmos comprised of dark matter is important in comparison only 3% of the mass of Universe consists of 'ordinary' matter.
"The motions of the galaxies inside the groups provide a direct method for studying the properties of dark matter", says Dr Aaron Robotham who leads the group catalogue project. "Studying dark matter in galaxies is confused by normal processes such as star formation, while this unseen material dominates the motions of galaxies in groups."
Dr. Robotham describes the construction of the group catalogue, which is a significant improvement on previous similar attempts with much shallower surveys. "The sample has some of the most massive bound structures ever measured. These range from the equivalent of a million billion times the mass of the Sun down to a mere few thousand billion solar masses. To have this range of dark matter halo masses within a single study is unprecedented."
It will take a further few years of detailed studies, with a large range of models, before a definite conclusion can be reached on whether the new GAMA data and supercomputer predictions (based on the popular Cold Dark Matter model of the Universe) are in good agreement or not.
"Currently the differences seen between the model and the data can be understood as limitations in the galaxy formation model used, explaining why intense modelling and further studies are required, and hopefully leading to some exciting new findings in the years ahead with possibly the first new insight into the properties of dark matter particles," adds Dr. Norberg.
GAMA team leader Professor Simon Driver of the University of St Andrews and the International Centre for Radio Astronomy Research at the University of Western Australia, says this group catalogue is the first big step of 4 years of data gathering by the GAMA Team at the Anglo-Australian Telescope. "The catalogue will provide the opportunity to study how gravity works over an unprecedented mass range and using data from other telescopes around the world we will shed fresh light on how dark mater helps to turn gas into stars".