| A team of 25 astronomers from Europe and Northern America, including ASTRON astronomers Morganti, Oosterloo, and Serra, has shown that many galaxies that are normally classified as early-type spheroidal galaxies are in fact more like disk galaxies. The so-called ATLAS3D team observed a sample of 260 galaxies with the SAURON spectrograph on the 4.2-meter William Herschel Telescope on La Palma, which allowed them to determine the motions of the stars in these carefully selected galaxies.
The team proposes a revision of the 70 year old Hubble tuning fork in which the vast majority of early-type galaxies are close relatives of spiral galaxies and for this reason form a parallel sequence to them. The new paradigm highlights a much closer connection between early-type and spiral galaxies than previously thought, and this will need to be considered in future models of how galaxies form. The above results were presented in three ATLAS3D team papers which will appear this month on the journal Monthly Notices of the Royal Astronomical Society.
The new results were unexpected and reveal a new paradigm for early-type galaxies. For the first time, it was found that the overwhelming majority of the early-type galaxies in the nearby Universe does not consist of roundish spheroidal objects, but instead has disks and more resemble spiral galaxies with the gas and dust removed. Only a tiny fraction of the early-type galaxies - the "slow rotators" - are genuine spheroids.