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.

Cosmological models predict that galaxies forming in the early Universe experience a chaotic phase of gas accretion and star formation, followed by gas ejection due to feedback processes. Galaxy bulges may assemble later via mergers or internal evolution. Here we present submillimeter observations (with spatial resolution of 700 parsecs) of ALESS 073.1, a starburst galaxy at redshift z≃5 when the Universe was 1.2 billion years old. This galaxy’s cold gas forms a regularly rotating disk with negligible noncircular motions. The galaxy rotation curve requires the presence of a central bulge in addition to a star-forming disk. We conclude that massive bulges and regularly rotating disks can form more rapidly in the early Universe than predicted by models of galaxy formation.

We derive the stellar-to-halo specific angular momentum relation (SHSAMR) of galaxies at z = 0 by combining i) the standard ΛCDM tidal torque theory ii) the observed relation between stellar mass and specific angular momentum (Fall relation) and iii) various determinations of the stellar-to-halo mass relation (SHMR). We find that the ratio f j = j * /j h of the specific angular momentum of stars to that of the dark matter i) varies with mass as a double power-law, ii) it always has a peak in the mass range explored and iii) it is 3 − 5 times larger for spirals than for ellipticals. The results have some dependence on the adopted SHMR and we provide fitting formulae in each case. For any choice of the SHMR, the peak of f j occurs at the same mass where the stellar-to-halo mass ratio f * = M * /M h has a maximum. This is mostly driven by the straightness and tightness of the Fall relation, which requires f j and f * to be correlated with each other roughly as f j ∝ f 2/3 * , as expected if the outer and more angular momentum rich parts of a halo failed to accrete onto the central galaxy and form stars (biased collapse). We also confirm that the difference in the angular momentum of spirals and ellipticals at a given mass is too large to be ascribed only to different spins of the parent dark-matter haloes (spin bias).

We present a study of the gas cycle and star formation history in the central 500 pc of the Milky Way, known as Central Molecular Zone (CMZ). Through hydrodynamical simulations of the inner 4.5 kpc of our Galaxy, we follow the gas cycle in a completely self-consistent way, starting from gas radial inflow due to the Galactic bar, the channelling of this gas into a dense, star-forming ring/stream at ≈ 200 − 300 pc from the Galactic centre, and the launching of galactic outflows powered by stellar feedback. We find that star formation activity in the CMZ goes through oscillatory burst/quench cycles, with a period of tens to hundreds of Myr, characterised by roughly constant gas mass but order-of-magnitude level variations in the star formation rate. Comparison with the observed present-day star formation rate of the CMZ suggests that we are currently near a minimum of this cycle. Stellar feedback drives a mainly two-phase wind off the Galactic disc. The warm phase dominates the mass flux, and carries 100 − 200% of the gas mass converted into stars. However, most of this gas goes into a fountain and falls back onto the disc rather than escaping the Galaxy. The hot phase carries most of the energy, with a time-averaged energy outflow rate of 10 − 20% of the supernova energy budget.

We present the results of a new sensitive survey of neutral hydrogen above and below the Galactic Center with the Green Bank Telescope. The observations extend up to Galactic latitude with an effective angular resolution of 9.′5 and an average rms brightness temperature noise of 40 mK in a 1 channel. The survey reveals the existence of a population of anomalous high-velocity clouds extending up to heights of about 1.5 kpc from the Galactic plane and showing no signature of Galactic rotation. These clouds have local standard of rest velocities , and assuming a Galactic Center origin, they have sizes of a few tens of parsec and neutral hydrogen masses spanning . Accounting for selection effects, the cloud population is symmetric in longitude, latitude, and V LSR. We model the cloud kinematics in terms of an outflow expanding from the Galactic Center and find the population consistent with being material moving with radial velocity distributed throughout a bicone with opening angle . This simple model implies an outflow luminosity erg s−1 over the past 10 Myr, consistent with star formation feedback in the inner region of the Milky Way, with a cold gas mass-loss rate . These clouds may represent the cold gas component accelerated in the nuclear wind driven by our Galaxy, although some of the derived properties challenge current theoretical models of the entrainment process.