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Early Growing Supermassive Black Holes Strengthen Stellar Bars

Presentation #101.04 in the session Galaxy Dynamics 1: Spirals and Bars.

Published onJul 01, 2023
Early Growing Supermassive Black Holes Strengthen Stellar Bars

Using N-body simulations we explore the effects of a growing supermassive black hole (SMBH) on the evolution and morphology of a stellar bar. Keeping the final mass and growth rate of the SMBH fixed, we show that when the SMBH is introduced before the bar reaches a steady state, the bar strength is always increased, compared to bars in models with no SMBH. The introduction of an SMBH in a growing bar also significantly alters the process of bar buckling, either decreasing the buckling amplitude, delaying buckling, or both. The impact on buckling is caused by an increase in the disk’s vertical velocity dispersion well beyond the nominal black hole sphere-of-influence and a consequent decrease in the susceptibility to the buckling instability. SMBH-induced disk heating also increases the strength of the Inner Lindblad Resonance (ILR) and the vertical ILR thereby strengthening the bar and the boxy-peanut/X shape. Using orbital frequency analysis of disk particles, we show that when an SMBH is introduced early and the bar forms around it, the bar is populated by different families of regular bar-supporting orbits than when the bar forms without an SMBH. A bar is weakened if an SMBH is introduced after the bar has reached a steady state, consistent with previous findings. In this case the SMBH weakens the bar by scattering bar-scattering bar supporting orbits at small pericenter radii, as previously shown by others. If the bar in the control model does not attain a steady state after buckling, the SMBH still delays or weakens buckling but the strengthing effects on the final bar amplitude are reduced. In no case do we find that an early growing SMBH weakens a bar. The authors gratefully acknowledge funding from the National Science Foundation (grants NSF-AST-1515001, NSF-AST-2009122), NASA-ATP grant 80NSSC20K0509 and the Space Telescope Science Institute (grant JWST-ERS-155701364.002-A) to M. Valluri.

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