Double-Barred Galaxies
نویسندگان
چکیده
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 doublebarred; 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.
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