We use the ATLAS ^ { \mathrm { 3 D } } sample to perform a study of the intrinsic shapes of early-type galaxies , taking advantage of the available combined photometric and kinematic data .
Based on our ellipticity measurements from the Sloan Digital Sky Survey Data Release 7 , and additional imaging from the Isaac Newton Telescope , we first invert the shape distribution of fast and slow rotators under the assumption of axisymmetry .
The so-obtained intrinsic shape distribution for the fast rotators can be described with a Gaussian with a mean flattening of q = 0.25 and standard deviation \sigma _ { q } = 0.14 , and an additional tail towards rounder shapes .
The slow rotators are much rounder , and are well described with a Gaussian with mean q = 0.63 and \sigma _ { q } = 0.09 .
We then checked that our results were consistent when applying a different and independent method to obtain intrinsic shape distributions , by fitting the observed ellipticity distributions directly using Gaussian parametrisations for the intrinsic axis ratios .
Although both fast and slow rotators are identified as early-type galaxies in morphological studies , and in many previous shape studies are therefore grouped together , their shape distributions are significantly different , hinting at different formation scenarios .
The intrinsic shape distribution of the fast rotators shows similarities with the spiral galaxy population .
Including the observed kinematic misalignment in our intrinsic shape study shows that the fast rotators are predominantly axisymmetric , with only very little room for triaxiality .
For the slow rotators though there are very strong indications that they are ( mildly ) triaxial .