HI angular momentum mass relation

TL;DR

This study reveals a consistent power-law relation between H I specific angular momentum and mass across a wide galaxy mass range, challenging existing models and highlighting the role of recent accretion and mergers.

Contribution

It provides the first comprehensive observational measurement of the H I angular momentum-mass relation over a broad mass range, showing a power-law slope distinct from dark matter halo predictions.

Findings

H I angular momentum scales as M_g^0.89 across 10^7 to 10^10.5 M_sun.

Ultra diffuse galaxies follow the same angular momentum relation as typical galaxies.

Early-type galaxies with large H I disks deviate, showing higher angular momentum due to recent accretion.

Abstract

We study the relationship between the H{\sc i} specific angular momentum (j$_{\rm g}$) and the H{\sc i} mass (M$_{\rm g}$) for a sample of galaxies with well measured H{\sc i} rotation curves. We find that the relation is well described by an unbroken power law \jg $\propto$ \mg$^{\alpha}$ over the entire mass range (10$^{7}$-10$^{10.5}$ M$_{\odot}$), with $\alpha = 0.89 \pm 0.05$ (scatter 0.18 dex). This is in reasonable agreement with models which assume that evolutionary processes maintain H{\sc i} disks in a marginally stable state. The slope we observe is also significantly different from both the $j \propto M^{2/3}$ relation expected for dark matter haloes from tidal torquing models and the observed slope of the specific angular momentum-mass relation for the stellar component of disk galaxies. Our sample includes two H{\sc i}-bearing ultra diffuse galaxies, and we find that their angular momentum follows the same relation as other galaxies. The only discrepant galaxies in our sample are early-type galaxies with large rotating H{\sc i} disks which are found to have significantly higher angular momentum than expected from the power law relation. The H{\sc i} disks of all these early-type galaxies are misaligned or counter-rotating with respect to the stellar disks, consistent with the gas being recently accreted. We speculate that late stage wet mergers, as well as cold flows play a dominant role in determining the kinematics of the baryonic component of galaxies as suggested by recent numerical simulations.