Origin of Non-axisymmetric Features of Virgo Cluster Early-type Dwarf Galaxies. II. Tidal Effects on Disk Features and Stability

TL;DR

This study uses N-body simulations to explore how tidal forces from clusters and galaxy interactions influence the formation and evolution of disk features like bars and spiral arms in dwarf galaxies, revealing that tides can trigger early bar formation and generate transient spiral arms.

Contribution

It demonstrates that tidal effects from clusters and galaxy interactions can induce and influence disk features in dwarf galaxies, providing insights into their origin and stability.

Findings

Tidal forces cause earlier bar formation by 1-1.5 Gyr compared to isolated cases.

Galactic halos lose mass significantly, but stellar disks remain largely unaffected.

Tidal interactions generate transient, kinematic spiral arms that decay over time.

Abstract

A fraction of dwarf galaxies in the Virgo cluster contain disk features like bars and spiral arms. Using $N$-body simulations, we investigate the effects of tidal forces on the formation of such disk features in disk dwarf galaxies resembling VCC856. We consider 8 Cluster-Galaxy models in which disk dwarf galaxies with differing pericenter distance and spin orientation experience the tidal gravitational force of a Virgo-like NFW halo, and additional 8 Galaxy-Galaxy models in which two dwarf galaxies undergo tidal interactions with different strength. We find that the cluster tidal effect is moderate due to the small galaxy size, making the bars form earlier by $\sim1$--$1.5\Gyr$ compared to the cases in isolation. While the galactic halos significantly lose their mass within the virial radius due to the cluster tidal force, the mass of the stellar disks is nearly unchanged, suggesting that the inner regions of a disk-halo system is secured from the tidal force. The tidal forcing from either the cluster potential or a companion galaxy triggers the formation of two-armed spirals at early time before a bar develops. The tidally-driven arms decay and wind with time, suggesting that they are kinematic density waves. In terms of the strength and pitch angle, the faint arms in VCC856 are best matched with the arms in a marginally unstable galaxy produced by a distant tidal encounter with its neighbor $\sim0.85\Gyr$ ago.