Most Massive Galaxies have Surprisingly Diverse Origins

14 May 2007

An Australian team, led by Sarah Brough of the Swinburne University of Technology used the Gemini South Telescope to find that the most massive galaxies evolve through a variety of mechanisms which are dependent on the mass of their cluster environment. These observations are not consistent with any single model of galaxy formation, presenting a challenge for theorists.

Brightest cluster galaxies (BCGs) are the most massive galaxies known. They are generally red, elliptical type galaxies with remarkably similar brightnesses that are only found near the centers of galaxy clusters. To understand how galaxies form and evolve it is vitally important to understand the formation of these massive galaxies. The uniformity of BCGs suggests that they have experienced similar evolutionary histories and their position at the centers of clusters suggests that their histories must be connected to their environment.

Current models of galaxy formation predict that the stars in these most massive galaxies should have formed more than 12 Billion years ago, while the galaxies themselves should have undergone many