Low Angular Momentum in Clumpy, Turbulent Disk Galaxies

TL;DR

This study measures stellar angular momentum in nearby clumpy, turbulent disk galaxies and finds it significantly lower than in typical local spirals, linking low angular momentum to galaxy stability and evolution.

Contribution

It provides the first direct measurements of stellar angular momentum in low-z analogs of high-z clumpy disks, revealing their angular momentum deficiency and its implications.

Findings

Target galaxies have about three times less stellar angular momentum than typical local spirals.

Low angular momentum is the main cause of low stability in these galaxies.

Angular momentum deficiency aligns with theoretical expectations from cosmic expansion effects.

Abstract

We measure the stellar specific angular momentum jstar=Jstar/Mstar in four nearby (z~0.1) disk galaxies that have stellar masses Mstar near the break M* of the galaxy mass function, but look like typical star-forming disks at z~2 in terms of their low stability (Q~1), clumpiness, high ionized gas dispersion (40-50 km/s), high molecular gas fraction (20-30%) and rapid star formation (~20 Msun/yr). Combining high-resolution (Keck-OSIRIS) and large-radius (Gemini-GMOS) spectroscopic maps, only available at low z, we discover that these targets have about three times less stellar angular momentum than typical local spiral galaxies of equal stellar mass and bulge fraction. Theoretical considerations show that this deficiency in angular momentum is the main cause of their low stability, while the high gas fraction plays a complementary role. Interestingly, the low jstar values of our targets are similar to those expected in the M*-population at higher z from the approximate theoretical scaling jstar~(1+z)^(-1/2) at fixed Mstar. This suggests that a change in angular momentum, driven by cosmic expansion, is the main cause for the remarkable difference between clumpy M*-disks at high z (which likely evolve into early-type galaxies) and mass-matched local spirals.