Effects of the Central Mass Concentration on Bar Formation in Disk Galaxies

Abstract

While bars are common in disk galaxies, their formation conditions are not well understood. We use $N$-body simulations to study bar formation and evolution in isolated galaxies consisting of a stellar disk, a classical bulge, and a dark halo. We consider 24 galaxy models that are similar to the Milky Way but differ in the mass and compactness of the classical bulge and halo concentration. We find that the bar formation requires $(Q_{T,\text{min}}/1.2{)}^2+(\text{CMC}/0.05{)}^2\lesssim 1$, where $Q_{T,\text{min}}$ and CMC refers to the minimum value of the Toomre stability parameter and the central mass concentration, respectively. Bars tend to be stronger, longer, and rotate slower in galaxies with a less massive and less compact bulge and halo. All bars formed in our models correspond to slow bars. A model with the bulge mass of $\sim 10$--$20$\% of the disk under a concentrated halo produces a bar similar to the Milky-Way bar. We discuss our findings in relation to other bar formation criteria suggested by previous studies.

Accepted for publication in ApJ

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• Galaxy formation physics behind bar formation: A view from cosmological hydrodynamical simulations
• Unraveling Joint Evolution of Bars, Star Formation, and Active Galactic Nuclei of Disk Galaxies
• Bar instability and formation timescale across Toomre's $Q$ parameter and central mass concentration: slow bar formation or true stability
• Dependence of galactic bars on the tidal density field in the SDSS
• Morphological evolution of disk galaxies and their concentration, asymmetry and clumpiness (CAS) properties in simulations across Toomre's $Q$ parameter
• Dynamical analysis of Maclaurin disk with velocity dispersion and its influence on bar formation
• Search for Slow Bars in Two Barred Galaxies with Nuclear Structures: NGC 6951 and NGC 7716