The ATLAS3D project – XVII. Linking photometric and kinematic signatures of stellar discs in early-type galaxies

Abstract

We analyse the morphological structures in galaxies of the ATLAS 3D sample by fitting a single Srsic profile and decomposing all non-barred objects (180 of 260 objects) in two components parametrized by an exponential and a general Srsic function. The aim of this analysis is to look for signatures of discs in light distributions of nearby early-type galaxies and compare them to kinematic properties. Using Srsic index from single-component fits for a distinction between slow and fast rotators, or even late-and early-type galaxies, is not recommended. Assuming that objects with n > 3 are slow rotators (or ellipticals), there is only a 22 per cent probability to correctly classify objects as slow rotators (or 37 per cent of previously classified as ellipticals). We show that exponential sub-components, as well as light profiles fitted with only a single component of a low Srsic index, can be linked with the kinematic evidence for discs in early-type galaxies. The median disc-to-total light ratio for fast and slow rotators is 0.41 and 0.0, respectively. Similarly, the median Srsic indices of the bulge (general Srsic component) are 1.7 and 4.8 for fast and slow rotators, respectively. Overall, discs or disc-like structures are present in 83 per cent of early-type galaxies which do not have bars, and they show a full range of disc-to-total light ratios. Discs in early-type galaxies contribute with about 40 per cent to the total mass of the analysed (non-barred) objects. The decomposition into