18 février 2020Long-lived double-bars in galaxies

Double-barred galaxies account for almost one third of all barred galaxies, suggesting that nuclear/inner stellar bars, which are embedded in large-scale primary bars, are long-lived structures. However, up to now it has been hard to self-consistently simulate a disc galaxy that sustains two nested stellar bars for longer than a few  rotation periods (typically less than 0.5 Gyr) in presence of a gas component. The only reported successful cases are based on pure N-body simulations and/or fine-tuned initial conditions. I have performed a series of numerical simulations of disc galaxies with an N-body + hydro code, including well-tested star formation recipes. The goal was to clarify the dynamical and physical requirements for long-lived triaxiality in the central region of galaxies. I show that double-bars can be long-lived (at least 7 Gyr) in presence of a gaseous component, even in the absence of dynamical resonance overlaps or mode couplings between the two bars, provided that star formation remains active, even at a moderate rate, in the central region where the nuclear bar lies.