No abstract

In a ΛCDM Universe, the specific stellar angular momentum ( j * ) and stellar mass (M * ) of a galaxy are correlated as a consequence of the scaling existing for dark matter haloes ( j h ∝ M 2/3 h ). The shape of this law is crucial to test galaxy formation models, which are currently discrepant especially at the lowest masses, allowing to constrain fundamental parameters, e.g. the retained fraction of angular momentum. In this study, we accurately determine the empirical j * − M * relation (Fall relation) for 92 nearby spiral galaxies (from S0 to Irr) selected from the Spitzer Photometry and Accurate Rotation Curves (SPARC) sample in the unprecedented mass range 7 log M * /M 11.5. We significantly improve all previous estimates of the Fall relation by determining j * profiles homogeneously for all galaxies, using extended Hi rotation curves, and selecting only galaxies for which a robust j * could be measured (converged j * (< R) radial profile). We find the relation to be well described by a single, unbroken power-law j * ∝ M α * over the entire mass range, with α = 0.55 ± 0.02 and orthogonal intrinsic scatter of 0.17 ± 0.01 dex. We finally discuss some implications for galaxy formation models of this fundamental scaling law and, in particular, the fact that it excludes models in which discs of all masses retain the same fraction of the halo angular momentum.

Dwarf Irregular galaxies (dIrrs) are the smallest stellar systems with extended HI discs. The study of the kinematics of such discs is a powerful tool to estimate the total matter distribution at these very small scales. In this work, we study the HI kinematics of 17 galaxies extracted from the 'Local Irregulars That Trace Luminosity Extremes, The HI Nearby Galaxy Survey' (LITTLE THINGS). Our approach differs significantly from previous studies in that we directly fit 3D models (two spatial dimensions plus one spectral dimension) using the software 3D BAROLO, fully exploiting the information in the HI datacubes. For each galaxy we derive the geometric parameters of the HI disc (inclination and position angle), the radial distribution of the surface density, the velocity-dispersion (σ v ) profile and the rotation curve. The circular velocity (V c ), which traces directly the galactic potential, is then obtained by correcting the rotation curve for the asymmetric drift. As an initial application, we show that these dIrrs lie on a baryonic Tully-Fisher relation in excellent agreement with that seen on larger scales. The final products of this work are high-quality, ready-to-use kinematic data (V c and σ v ) that we make publicly available. These can be used to perform dynamical studies and improve our understanding of these low-mass galaxies.

The study of the evolution of star-forming galaxies requires the determination of accurate kinematics and scaling relations out to high redshift. In this paper we select a sample of 18 galaxies at z ∼ 1, observed in the Hα emission-line with KMOS, to derive accurate kinematics using a novel 3D analysis technique. We use the new code 3D Barolo that models the galaxy emission directly in the 3D observational space, without the need to extract kinematic maps. This technique's major advantage is that it is not affected by beam smearing and thus it enables the determination of rotation velocity and intrinsic velocity dispersion, even at low spatial resolution. We find that: 1) the rotation curves of these z ∼ 1 galaxies rise very steeply within few kiloparsecs and remain flat out to the outermost radius and 2) the Hα velocity dispersions are low, ranging from 15 to 40 km s −1 , which leads to V/σ = 3-10. These characteristics are similar to those of disc galaxies in the local Universe. Finally, we also report no significant evolution of the stellar-mass Tully-Fisher relation. Our results show that disc galaxies are kinematically mature and rotation-dominated already at z ∼ 1.