Why are some galaxy disks extremely thin?

TL;DR

This paper investigates the physical reasons behind the extremely thin stellar disks in some low surface brightness galaxies, emphasizing the role of dark matter halos in their structure.

Contribution

It models stellar thickness in two-component disks within dark matter halos, highlighting the impact of compact halos on superthin galaxy disks, a novel insight.

Findings

Compact dark matter halos are crucial for superthin disk formation.

Gas presence constrains but does not determine disk thickness.

Dark matter halo properties influence early galaxy evolution.

Abstract

Some low surface brightness galaxies are known to have extremely thin stellar disks with the vertical to planar axes ratio 0.1 or less, often referred to as superthin disks. Although their existence is known for over three decades, the physical origin for the thin distribution is not understood. We model the stellar thickness for a two-component (gravitationally coupled stars and gas) disk embedded in a dark matter halo, for a superthin galaxy UGC 7321 which has a dense, compact halo, and compare with a typical dwarf galaxy HoII which has a non-compact halo. We show that while the presence of gas does constrain the disk thickness, it is the compact dark matter halo which plays the decisive role in determining the superthin disk distribution in low-mass disks. Thus the compact dark matter halo significantly affects the disk structure and this could be important for the early evolution of galaxies.