Rotation curve bifurcations as indicators of close recent galaxy encounters

TL;DR

This study uses 3D simulations to show that bifurcations in galaxy rotation curves during close encounters can serve as indicators of recent pericentre passage, occurring within a short time window.

Contribution

It demonstrates that rotation curve bifurcations are reliable markers of close galaxy encounters, based on detailed simulation analysis.

Findings

Rotation curve asymmetries appear at pericentre.

Disturbed velocities occur within ~0.5 Gyr.

Bifurcations indicate recent close encounters.

Abstract

Rotation curves of interacting galaxies often show that velocities are either rising or falling in the direction of the companion galaxy. We seek to reproduce and analyse these features in the rotation curves of simulated equal-mass galaxies suffering a one-to-one encounter, as possible indicators of close encounters. Using simulations of major mergers in 3D, we study the time evolution of these asymmetries in a pair of galaxies, during the first passage. Our main results are: (a) the rotation curve asymmetries appear right at pericentre of the first passage, (b) the significant disturbed rotation velocities occur within a small time interval, of ~ 0.5 Gyr h^-1, and therefore the presence of bifurcation in the velocity curve could be used as an indicator of the pericentre occurrence. These results are in qualitative agreement with previous findings for minor mergers and fly-byes.