Long-lived Double-barred Galaxies from Pseudobulges

A large fraction of barred galaxies host secondary bars that are embedded intheir large-scale primary counterparts. These are common also in gas poorearly-type barred galaxies. The evolution of such double-barred galaxies isstill not well understood, partly because of a lack of realistic $N$-bodymodels with which to study them. Here we report a new mechanism for generatingsuch systems, namely the presence of rotating pseudo-bulges. We demonstate withhigh mass and force resolution collisionless $N$-body simulations thatlong-lived secondary bars can form spontaneously without requiring gas,contrary to previous claims. We find that secondary bars rotate faster thanprimary ones. The rotation is not, however, rigid: the secondary bars pulsate,with their amplitude and pattern speed oscillating as they rotate through theprimary bars. This self-consistent study supports previous work based onorbital analysis in the potential of two rigidly rotating bars. The pulsatingnature of secondary bars may have important implications for understanding thecentral region of double-barred galaxies.Comment: Paper submitted to ApJ