Angular Momentum of Dwarf Galaxies

TL;DR

This study measures the angular momentum of dwarf irregular galaxies, revealing higher specific angular momentum than larger galaxies and a dependence on baryon mass fraction, providing insights into galaxy formation.

Contribution

It extends angular momentum measurements to lower mass dwarf galaxies and analyzes the relationship between baryonic mass, angular momentum, and gas fractions.

Findings

Dwarf galaxies have higher specific angular momentum than expected from spiral galaxy scaling.

The specific angular momentum of HI is about 2.5 times that of stars.

The M-j relation for HI is steeper than for stars, influenced by HI fraction variation.

Abstract

We present measurements of baryonic mass Mb and specific angular momentum (sAM) jb in 14 rotating dwarf Irregular (dIrr) galaxies from the LITTLE THINGS sample. These measurements, based on 21cm kinematic data from the Very Large Array and stellar mass maps from the Spitzer Space Telescope, extend previous AM measurements by more than two orders of magnitude in Mb. The dwarf galaxies show systematically higher jb values than expected from the jb~Mb^{2/3} scaling of spiral galaxies, representative of a scale-free galaxy formation scenario. This offset can be explained by decreasing baryon mass fractions fM=Mb Mdyn (where Mdyn is the dynamical mass) with decreasing Mb (for Mb<10^{11}Msun). We find that the sAM of neutral atomic hydrogen HI alone is about 2.5 times higher than that of the stars. The M-j relation of HI is significantly steeper than that of the stars, as a direct consequence of the systematic variation of the HI fraction with Mb.