On the Kinematics, Stability and Lifetime of Kinematically Distinct Cores: A Case Study

TL;DR

This study uses a high-resolution simulation to analyze the formation, motion, and stability of kinematically distinct cores in early-type galaxies over 10 billion years, revealing their origin, precession behavior, and eventual dispersal.

Contribution

It provides a detailed case study of KDC evolution in a galaxy merger simulation, highlighting the dynamics and stability timescales of KDCs over cosmic time.

Findings

KDCs are formed by stars created during galaxy mergers.

KDCs exhibit precession similar to a gyroscope.

KDCs remain stable for about 3 Gyr before dispersing.

Abstract

We present a case study of a early-type galaxy (ETG) hosting a kinematically distinct core (KDC) formed in a binary high resolution 1:1 spiral galaxy merger simulation. The runtime of the simulation is pushed up to 10Gyr to follow the complete evolution of various physical properties. To investigate the origin of the KDC, the stellar component residing within the KDC is dissected, revealing that the rotational signal is purely generated by stars that belong to the KDC for at least 0.5Gyr and are newly formed during the merging process. Following the orientation of the total stellar angular momentum of the KDC, we show that it performs a motion comparable to the precession of a gyroscope in a gravitational potential. We draw the conclusion that the motion of the KDC is a superposition of an intrinsic rotation and a global precession that gets gradually damped over cosmic time. Finally, the stability of the KDC over the complete runtime of the simulation is investigated by tracing the evolution of the widely used $\lambda_{R}$ parameter and the misalignment angle distribution. We find that the KDC is stable for about 3Gyr after the merger and subsequently disperses completely on a timescale of ~1.5Gyr.