A minor-merger origin for inner disks and rings in early-type galaxies

TL;DR

This study uses collisionless N-body simulations to demonstrate that minor mergers can form inner disks and rings in early-type galaxies, explaining their origin without the need for bars.

Contribution

It provides the first detailed simulation-based evidence that minor mergers can produce inner disks and rings in galaxies, highlighting the role of satellite density and mass.

Findings

Minor mergers can create thin, kinematically cold inner structures.

Dense or massive satellites deposit material at the galaxy center, forming disks.

Less massive satellites disrupt before reaching the center, forming rings.

Abstract

Nuclear disks and rings are frequent galaxy substructures, for a wide range of morphological types (from S0 to Sc). We have investigated the possible minor-merger origin of inner disks and rings in spiral galaxies through collisionless N-body simulations. The models confirm that minor mergers can drive the formation of thin, kinematically-cold structures in the center of galaxies out of satellite material, without requiring the previous formation of a bar. Satellite core particles tend to be deposited in circular orbits in the central potential, due to the strong circularization experienced by the satellite orbit through dynamical friction. The material of the satellite core reaches the remnant center if satellites are dense or massive, building up a thin inner disk; whereas it is fully disrupted before reaching the center in the case of low-mass satellites, creating an inner ring instead.