The Prevalence of Type III Disc Breaks in HI-rich and Low-spin Galaxies

TL;DR

This study analyzes the occurrence of up-bending disc breaks in galaxies, revealing that HI-rich, low-spin galaxies have a higher prevalence of type III discs, supporting the role of gas accretion and in-situ star formation.

Contribution

It demonstrates the dependence of type III disc break prevalence on HI content and spin, highlighting gas accretion as a key mechanism in outer disc formation.

Findings

HI-rich, low-spin galaxies have more type III disc breaks.

Type III fraction depends on stellar concentration.

Results support gas accretion-driven outer disc growth.

Abstract

We investigate the origin of the type III (up-bending) discs based on a sample of 1808 galaxies from SDSS and a sub-sample of 286 galaxies with HI data from ALFALFA. We examine how the type III fraction f3, the fraction of disc galaxies which host up-bending disc breaks, depends on other galactic properties. We confirm that f3 strongly depends on the stellar concentration of galaxies. We find that HI-rich galaxies with low spins tend to have significantly more type III disc breaks than control galaxies, which are matched in concentration and stellar mass. This trend is independent of the existence of strong bars or environment of the galaxies. This result is broadly consistent with predictions from theoretical simulations, and indicates in-situ star formation fueled by gas accretion to be an important mechanism that builds the outer discs of type III galaxies.