Physical Properties of Tidal Features in Interacting Disk Galaxies

TL;DR

This study investigates the formation and evolution of tidal features in interacting disk galaxies, revealing how tidal forces create transient spiral arms, bridges, and tails with specific kinematic properties and decay timescales.

Contribution

It provides a detailed analysis of the physical mechanisms behind tidal feature formation, including phase locking and spiral arm development, with implications for observed galactic structures.

Findings

Tidal forces produce transient spiral arms, bridges, and tails with distinct characteristics.

Tidal tails are narrow, logarithmic-shaped arms that dissolve over ~1 Gyr.

Spiral arms form due to kinematic alignment and are influenced by self-gravity.

Abstract

We explore tidal interactions of a galactic disk with Toomre parameter Q ~ 2 embedded in rigid halo/bulge with a point mass companion moving in a prescribed parabolic orbit. Tidal interactions produce well-defined spiral arms and extended tidal features such as bridge and tail that are all transient, but distinct in nature. In the extended disks, strong tidal force is able to lock the perturbed epicycle phases of the near-side particles to the perturber, shaping them into a tidal bridge that corotates with the perturber. A tidal tail develops at the opposite side as strongly-perturbed, near-side particles overtake mildly-perturbed, far-side particles. The tail is essentially a narrow material arm with a roughly logarithmic shape, dissolving with time because of large velocity dispersions. Inside the disks where tidal force is relatively weak, on the other hand, a two-armed logarithmic spiral pattern emerges due to the kinematic alignment of perturbed particle orbits. While self-gravity makes the spiral arms a bit stronger, the arms never become fully self-gravitating, wind up progressively with time, and decay after the peak almost exponentially in a time scale of ~ 1 Gyr. The arm pattern speed varying with both radius and time converges to Omega-kappa/2 at late time, suggesting that the pattern speed of tidally-driven arms may depend on radius in real galaxies. We present the parametric dependences of various properties of tidal features on the tidal strength, and discuss our findings in application to tidal spiral arms in grand-design spiral galaxies. (Abridged)