Properties of Bars and Bulges in the Hubble Sequence

Abstract

Properties of bars and bulges in the Hubble sequence are discussed, based on the analysis of 216 disk galaxies (S0s and spirals from NIRS0S and OSUBGS surveys, respectively). For that purpose we have collected together, and completed when necessary, the various analysis we have previously made separately for early and late types. We find strong photometric and kinematic evidence of pseudobulges in the S0-S0/a galaxies: their bulges are on average fairly exponential, inner disks are common (in 56%), and in many of the galaxies the bulges are rotationally supported. This would be difficult to understand in such gas poor galaxies as in S0s, if these pseudobulge candidates were formed by star formation in the disk in a a similar manner as in spirals. A more likely explanation is that pseudobulges in the early-type galaxies are bar-related structures, connected to the evolution of bars, which interpretation is supported by our Fourier analysis and structural decompositions. Bars in the early-type galaxies are found to have many characteristics of evolved systems: (1) they have flat-top/double peaked Fourier amplitude profiles, (2) bars have typically sharp outer cut-offs, (3) the higher Fourier modes appear in the amplitude profiles, and (4) many bars have also ansae-type morphologies. We show the distributions of bar strength in different Hubble type bins using four bar strength indicators, $Q_g$, $A_2$, $f_{bar}$ and the bar length, which are expected to give important clues for understanding the mechanism of how bars evolve.

22 pages, 9 figures to be submitted to MNRAS

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• The STAGES view of red spirals and dusty red galaxies: Mass-dependent quenching of star-formation in cluster infall
• Model-based pattern speed estimates for 38 barred galaxies
• Bars, ovals and lenses in early-type disk galaxies: probes of galaxy evolution
• The Millennium Galaxy Catalogue: Exploring the Color-Concentration Bimodality via Bulge-Disc Decomposition
• Confirmation of a Kinematic Diagnostic for Face-On B/P Bulges
• Do Bars Drive Spiral Density Waves?
• Photometric characterization of a well defined sample of isolated galaxies in the context of the AMIGA project
• Comparison of bar strengths in optical and near-infrared for the OSUBSGS sample