Thin discs, thick dwarfs, and the importance of feedback effects

TL;DR

This study explores how stellar mass influences the intrinsic thickness of faint galaxies, revealing a mass threshold below which galaxies become systematically thicker due to feedback effects and turbulence.

Contribution

It identifies a critical stellar mass where galaxy thickness increases, linking feedback and angular momentum to galaxy morphology in faint systems.

Findings

Galaxies below ~2x10^9 Msun are systematically thicker.

Good agreement with numerical simulations of dwarf galaxy formation.

Implications for bar and spiral formation, HI profile deprojection, and environmental effects.

Abstract

We investigate the role of stellar mass in shaping the intrinsic thickness of faint systems by determining the probability distribution of apparent axis ratios for two different samples that probe the faint end of the galaxy luminosity function (M_B < -8). We find that the (b/a) distribution is a strong function of M*, and identify a limiting stellar mass M* ~ 2x10^9 Msun below which galaxies start to be systematically thicker. We argue that this is the result of the complex interplay between galaxy mass, specific angular momentum and stellar feedback effects: the increasing importance of turbulent motions in lower mass galaxies leads to the formation of thicker systems. We find a good agreement between our results and the latest numerical simulations of dwarf galaxy formation, and discuss several further implications of this finding --including the formation of bars and spirals in faint galaxies, the deprojection of HI line profiles and simulations of environmental effects on dwarf galaxies.