Formation of Dwarf Spheroidal Galaxies Via Mergers of Disky Dwarfs

TL;DR

This study uses N-body simulations to show that mergers of rotationally-supported dwarf galaxies can produce dwarf spheroidal galaxies with properties similar to those observed in the Local Group, especially in isolated regions.

Contribution

It demonstrates through simulations that binary mergers of dwarf disks can form dSphs, providing a new formation pathway supported by cosmological context.

Findings

At least three simulated mergers produce dSph-like systems.

Two dSph-like remnants remain isolated, resembling remote LG dwarf galaxies.

Merging dwarfs is a viable formation mechanism for dSphs in the Local Group.

Abstract

We perform collisionless N-body simulations to investigate whether binary mergers between rotationally-supported dwarfs can lead to the formation of dwarf spheroidal galaxies (dSphs). Our simulation campaign is based on a hybrid approach combining cosmological simulations and controlled numerical experiments. We select merger events from a Constrained Local UniversE (CLUES) simulation of the Local Group (LG) and record the properties of the interacting dwarf-sized halos. This information is subsequently used to seed controlled experiments of binary encounters between dwarf galaxies consisting of exponential stellar disks embedded in cosmologically-motivated dark matter halos. These simulations are designed to reproduce eight cosmological merger events, with initial masses of the interacting systems in the range ~ (5-60) x 10^7 Mo, occurring quite early in the history of the LG, more than 10 Gyr ago. We compute the properties of the merger remnants as a distant observer would and demonstrate that at least three of the simulated encounters produce systems with kinematic and structural properties akin to those of the classic dSphs in the LG. Tracing the history of the remnants in the cosmological simulation to z=0, we find that two dSph-like objects remain isolated at distances larger than 800 kpc from either the Milky Way or M31. These systems constitute plausible counterparts of the remote dSphs Cetus and Tucana which reside in the LG outskirts, far from the tidal influence of the primary galaxies. We conclude that merging of rotationally-supported dwarfs represents a viable mechanism for the formation of dSphs in the LG and similar environments.