To appear in "Tumbling, Twisting, and Winding Galaxies: Pattern Speeds along the Hubble Sequence", E. M. Corsini and V. P. Debattista (eds.), Memorie della Societa` Astronomica Italiana
astro-ph/0908.0909

For a PDF version of the article, click here.

Abstract. I present a brief review of what is known about double-barred galaxies, where a small ("inner") bar is nested inside a larger ("outer") bar; the review is focused primarily on their demographics and photometric properties. Roughly 20% of S0-Sb galaxies are double-barred; they may be rarer in later Hubble types. Inner bars are typically ~ 500 pc in radius (~ 12% the size of outer bars), but sizes range from ~ 100 pc to > 1 kpc. The structure of at least some inner bars appears very similar to that of outer bars (and single large-scale bars). Direct and indirect evidence all support the hypothesis that inner bars rotate independently of outer bars, although actual pattern speeds for inner bars are poorly constrained. Finally, I note that inner bars do not appear to promote nuclear activity.

Keywords: Galaxies: active - Galaxies: elliptical and lenticular, cD - Galaxies: kinematics and dynamics - Galaxies: spiral - Galaxies: photometry - Galaxies: structure

Table of Contents

• INTRODUCTION
• DEMOGRAPHICS
• THE STRUCTURE OF INNER BARS
• Dissections
• PATTERN SPEEDS
• DOUBLE BARS AND AGN?
• REFERENCES