2008AJ....136..773F

In this paper, we study the properties of pseudobulges (bulges that appear similar to disk galaxies) and classical bulges (bulges which appear similar to E-type galaxies) in bulge-disk decompositions. We show that the distribution of bulge Sérsic indices, n_b, is bimodal, and this bimodality correlates with the morphology of the bulge. Pseudobulges have n_b≲ 2 and classical bulges have n_b≳ 2 with little to no overlap. Also, pseudobulges do not follow the correlations of Sérsic index with structural parameters or the photometric projections of the fundamental plane in the same way that classical bulges and elliptical galaxies do. We find that pseudobulges are systematically flatter than classical bulges and thus more disk-like in both their morphology and shape. We do not find significant differences between different bulge morphologies which we are collectively calling pseudobulges (nuclear spirals, nuclear rings, nuclear bars, and nuclear patchiness); they appear to behave similarly in all parameter correlations. In the Sérsic index, flattening, and bulge-to-total ratio, the distinction appears to be between classical bulges and pseudobulges, not between different pseudobulge morphologies. The Sérsic index of the pseudobulges does not correlate with B/T, in contrast to classical bulges. Also, the half-light radius of the pseudobulge correlates with the scale length of the disk; this is not the case for classical bulges. The correlation of Sérsic index and scale lengths with bulge morphology suggests that secular evolution is creating pseudobulges with low-Sérsic index and that other processes (e.g., major mergers) are responsible for the higher Sérsic index in classical bulges and elliptical galaxies.