Ring galaxies from off-centre collisions

TL;DR

This study uses N-body/SPH simulations to explore how off-centre collisions can produce ring galaxies with an empty ring, matching observations and revealing effects on galaxy structure and star formation.

Contribution

It demonstrates that off-centre collisions can form RE galaxies with various ring shapes and displacements, incorporating star formation and feedback in realistic galaxy models.

Findings

RE galaxies can form via off-centre collisions with small inclination angles.

The nucleus is displaced and buried within the ring, not vertically displaced.

Interaction enhances star formation rate in the simulated galaxies.

Abstract

We investigate the formation of RE galaxies (i.e. of collisional ring galaxies with an empty ring), with N-body/SPH simulations. The simulations employ a recipe for star formation (SF) and feedback that has been shown to be crucial to produce realistic galaxies in a cosmological context. We show that RE galaxies can form via off-centre collisions (i.e. with a non-zero impact parameter), even for small inclination angles. The ring can be either a complete ring or an arc, depending on the initial conditions (especially on the impact parameter). In our simulations, the nucleus of the target galaxy is displaced from the dynamical centre of the galaxy and is buried within the ring, as a consequence of the off-centre collision. We find that the nucleus is not vertically displaced from the plane of the ring. We study the kinematics of the ring, finding agreement with the predictions by the analytic theory. The SF history of the simulated galaxies indicates that the interaction enhances the SF rate. We compare the results of our simulations with the observations of Arp 147, that is the prototype of RE galaxies.