A morphological and statistical analysis of ansae in barred galaxies

Many barred galaxies show a set of symmetric enhancements at the ends of the stellar bar, called ansae, or the handles'' of the bar. Ansa bars have been in the literature for some decades, but their origin has still not been specifically addressed, although they could be related to the growth process of bars. But even though ansae have been known for a long time, no statistical analysis of their relative frequency of occurrence has been performed yet. Similarly, there has been no study of the varieties in the morphology of ansae, even though significant morphological variations are known to characterize the features. In this paper we make a quantitative analysis of the occurrence of ansae in barred galaxies, making use of The de Vaucouleurs Atlas of Galaxies by Buta and coworkers. We find that -40% of SB0's show ansae in their bars, thus confirming that ansae are common features in barred lenticulars. The ansa frequency decreases dramatically with later types, and hardly any ansae are found in galaxies of type Sb or later. The bars in galaxies with ansae are stronger in the median than those in galaxies without ansae, but the presence of inner and outer rings is not related to the presence of ansae. Implications of these results and theories for the possible origin of ansae are discussed briefly.