The baryonic specific angular momentum of disc galaxies

TL;DR

This study measures the baryonic specific angular momentum of disc galaxies, revealing tight power-law relations with mass and a consistent angular momentum retention fraction, providing key constraints for galaxy formation models.

Contribution

It provides the first homogeneous, high-accuracy measurements of stellar and gas specific angular momenta across a wide galaxy mass range, establishing unbroken power-law relations and a constant angular momentum retention fraction.

Findings

The $j_{ m *}$-$M_ m *$ relation is a power-law with slope 0.54.

The $j_{ m gas}$-$M_{ m gas}$ relation is a steeper power-law with slope 1.02.

The baryonic $j_{ m bar}$-$M_{ m bar}$ relation follows a power-law with slope 0.60.

Abstract

(Abridged) Specific angular momentum is one of the key parameters that control the evolution of galaxies. We derive the baryonic specific angular momentum of disc galaxies and study its relation with the dark matter specific angular momentum. Using a combination of high-quality HI rotation curves and HI/near-IR surface densities, we homogeneously measure the stellar ($j_{\rm *}$) and gas ($j_{\rm gas}$) specific angular momenta for a large sample of local disc galaxies. This allows us to determine the baryonic specific angular momentum ($j_{\rm bar}$) with high accuracy and across a very wide range of masses. The $j_{\ast}-M_\ast$ relation is an unbroken power-law from $7 \lesssim$ log($M_\ast$/$M_\odot) \lesssim 11.5$, with slope $0.54 \pm 0.02$. For the gas component, we find that the $j_{\rm gas}-M_{\rm gas}$ relation is also an unbroken power-law from $6 \lesssim$ log($M_{\rm gas}$/$M_\odot) \lesssim 11$, with a steeper slope of $1.02 \pm 0.04$. Regarding the baryonic relation, our data support a correlation characterized by single power-law with slope $0.60 \pm 0.02$. Our most massive spirals and smallest dwarfs lie along the same $j_{\rm bar}-M_{\rm bar}$ sequence. While the relations are tight and unbroken, we find internal correlations inside them: At fixed $M_\ast$, galaxies with larger $j_\ast$ have larger disc scale lengths, and at fixed $M_{\rm bar}$, gas-poor galaxies have lower $j_{\rm bar}$ than expected. We estimate the retained fraction of baryonic specific angular momentum, finding it constant across our entire mass range with a value of $\sim 0.6$, indicating that the $j_{\rm bar}$ of present-day disc galaxies is comparable to the initial specific angular momentum of their dark matter haloes. These results set important constraints for hydrodynamical simulations and semi-analytical models aiming to reproduce galaxies with realistic specific angular momenta.