Bar Fraction in Early- and Late-type Spirals

Bar fractions depend on the properties of the host galaxies, which are closely related to the formation and evolution of bars. However, observational studies do not provide consistent results. We investigate the bar fraction and its dependence on the properties of the host galaxies by using three bar classification methods: visual inspection, an ellipse fitting method, and Fourier analysis. Our volume-limited sample consists of 1698 spiral galaxies brighter than Mr = −15.2 with z < 0.01 from the Sloan Digital Sky Survey/DR7 visually classified by Ann et al. We first compare the consistency of classification among the three methods. Automatic classifications detect visually determined, strongly barred galaxies with the concordance of 74% to 85%. However, they have some difficulty in identifying bars, in particular in bulge-dominated galaxies, which affects the distribution of bar fraction as a function of Hubble type. We obtain, for the same sample, different bar fractions of 63%, 48%, and 36% by visual inspection, ellipse fitting, and Fourier analysis, respectively. The difference is mainly due to how many weak bars are included. Moreover, we find a different dependence of bar fraction on Hubble type for strong versus weak bars: SBs are preponderant in early-type spirals, whereas SABs are in late-type spirals. This causes a contradictory dependence on host galaxy properties when different classification methods are used. We propose that strong bars and weak bars experience different processes for their formation, growth, and dissipation by interacting with different inner galactic structures of early-type and late-type spirals.