The Edge-On Perspective of Bulgeless, Simple Disk Galaxies

TL;DR

This review discusses edge-on, bulgeless simple disk galaxies, highlighting their properties, significance in galaxy formation theories, and their role in understanding dark matter and galaxy evolution.

Contribution

It provides a comprehensive overview of simple disk galaxies, emphasizing their importance in testing galaxy formation models and understanding dark matter distribution.

Findings

Simple disks are low-mass, low surface brightness, blue, slow-rotating galaxies.

They challenge traditional cosmological models of galaxy formation.

Recent models better explain the existence of simple disk galaxies.

Abstract

This review focuses on flat and superthin galaxies. These are edge-on bulgeless galaxies, which are composed of a simple, stellar disk. The properties of these simple disks are at the end of a continuum that extends smoothly from bulge-dominated disk galaxies to the pure disks. On average, simple disks are low-mass galaxies with low surface brightnesses, blue colors, and slow rotational velocities. Widely-accepted cosmological models of galaxy formation and evolution were challenged by a relatively large observed fraction of pure disk galaxies, and only very recent models can explain the existence of simple disk galaxies. This makes simple disks an optimal galaxy type for the study of galaxy formation in a hierarchical Universe. They enable us to analyze the environmental and internal influence on galaxy evolution, to study the stability of the disks, and to explain the nature and distribution of dark matter in galaxies. This review summarizes the current status of edge-on simple disk galaxies in the Universe.