The baryonic specific angular momentum of disc galaxies^⋆

¹ Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
e-mail: pavel@astro.rug.nl
² ASTRON, Netherlands Institute for Radio Astronomy, Postbus 2, 7900 AA Dwingeloo, The Netherlands
³ Observatoire Astronomique de Strasbourg, Université de Strasbourg, 11 Rue de l’Université, 67000 Strasbourg, France

Received: 4 September 2020
Accepted: 2 January 2021

Abstract

Aims. Specific angular momentum (the angular momentum per unit mass, j = J/M) is one of the key parameters that control the evolution of galaxies, and it is closely related with the coupling between dark and visible matter. In this work, we aim to derive the baryonic (stars plus atomic gas) specific angular momentum of disc galaxies and study its relation with the dark matter specific angular momentum.

Methods. Using a combination of high-quality H I rotation curves, H I surface densities, and near-infrared surface brightness profiles, we homogeneously measure the stellar (j_*) and gas (j_gas) specific angular momenta for a large sample of nearby disc galaxies. This allows us to determine the baryonic specific angular momentum (j_bar) with high accuracy and across a very wide range of masses.

Results. We confirm that the j_* − M_* relation is an unbroken power-law from 7 ≲ log(M_*/M_⊙) ≲ 11.5, with a slope 0.54 ± 0.02, setting a stronger constraint at dwarf galaxy scales than previous determinations. Concerning the gas component, we find that the j_gas − M_gas relation is also an unbroken power-law from 6 ≲ log(M_gas/M_⊙) ≲ 11, with a steeper slope of 1.02 ± 0.04. Regarding the baryonic relation, our data support a correlation characterized by a single power-law with a slope 0.60 ± 0.02. Our analysis shows that our most massive spirals and smallest dwarfs lie along the same j_bar − M_bar sequence. While the relations are tight and unbroken, we find internal correlations inside them: At fixed M_*, galaxies with larger j_* have larger disc scale lengths, and at fixed M_bar, gas-poor galaxies have lower j_bar than expected. We estimate the retained fraction of baryonic specific angular momentum, f_j, bar, finding it constant across our entire mass range with a value of ∼0.6, indicating that the baryonic specific angular momentum of present-day disc galaxies is comparable to the initial specific angular momentum of their dark matter haloes. In general, these results set important constraints for hydrodynamical simulations and semi-analytical models that aim to reproduce galaxies with realistic specific angular momenta.