Stellar discs in massive galaxies

Excluding those unsettled systems undergoing mergers, bright galaxies come in two flavours: with and without discs. In this work we look for photometric evidence for presence of discs and compare it with kinematic results of the ATLAS 3D survey (Cappellari et al . 2011). We fit a Sersic (1968) function to azimuthally averaged light profiles of ATLAS 3D galaxies to derive single component fits and, subsequently, we fit a combination of the Sersic function (free index n ) and an exponential function ( n =1) with the purpose of decomposing the light profiles into “bulge” and “disc” components (B+D model) of all non-barred sample galaxies. We compare the residuals of the B+D models with those of the single Sersic fits and select the B+D model as preferred only when the improvement is substantial and there are no correlations within residuals. We find that the high angular momentum objects (fast rotators) are disc dominated systems with bulges of typically low n (when their light profiles can be decomposed) or are best represented with a single Sersic function with a low Sersic index ( n