Time-dependent Pattern Speeds in Barred Galaxies

Abstract

Based on a high quality $N$-body simulation of a double bar galaxy model, we investigate the evolution of the bar properties, including their size, strength and instantaneous pattern speed derived by using three distinct methods: the Fourier, Jacobi integral, and moment of inertia methods. The interaction of the two bars, which rotate at distinct speeds, primarily affects the size, strength and pattern speed of the inner bar. When the two bars are perpendicular to each other, the size and the pattern speed of the inner bar decrease and its strength increases. The emergence of a strong Fourier $m=1$ mode increases the oscillation amplitude of the size, strength and pattern speed of the inner bar. On the other hand, the characteristics of the outer bar are substantially influenced by its adjacent spiral structure. When the spiral structure disappears, the size of the outer bar increases and its strength and pattern speed decrease. Consequently, the ratio of the pattern speed of the outer bar with respect to the inner bar is not constant and increases with time. Overall, the double bar and disk system displays substantial high frequency semi-chaotic fluctuations of the pattern strengths and speeds both in space and time, superposed on the slow secular evolution, which invalidates the assumption that the actions of individual stars should be well conserved in barred galaxies, such as the Milky Way.

25 pages, 17 figures, 1 table. ApJ accepted

References in corpus (8)

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Cited by in corpus (8)

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• Mass inflow rate into the Central Molecular Zone: observational determination and evidence of episodic accretion
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• Applying the Tremaine-Weinberg Method to Nearby Galaxies: Stellar Mass-Based Pattern Speeds, and Comparisons with ISM Kinematics
• Bars formed in galaxy merging and their classification with deep learning
• Five methods for determining pattern speeds in galaxies
• Capturing the short-term characteristics of a barred galaxy from a single snapshot
• Age distribution of stars in boxy/peanut/X-shaped bulges formed without bar buckling