Gas Rotation Research Articles

RESISTANCE OF TANGENTIAL SWIRLERS WITH ANNULAR CHANNELS

A review of vortex apparatuses and processes in which a rotating gas-liquid flow is used as an intensification of heat and mass transfer is presented.
 It is shown that tangential swirlers, which are easy to manufacture and compact, have found the greatest application in industrial practice for creating gas (steam) rotation.
 It is experimentally established that tangential swirlers with annular walls of channels intended for gas passage have the lowest hydraulic resistance.
 The data on the hydraulic resistance of tangential swirlers with annular channels, velocity and pressure obtained experimentally and by calculation in a wide range of variation of the design parameters of the device are presented.
 The dependences between the hydraulic resistance of the swirler and its design parameters are revealed.
 Numerical simulation of the parameters of the gas flow in the channels is carried out. Diagrams of the pressure and velocity distribution are presented and analyzed, and experimental data on the influence of the design parameters of the swirler channel, such as width and length, on its hydraulic resistance are confirmed.
 An empirical dependence for determining the hydraulic resistance coefficient of a tangential swirler with annular channels is presented for engineering calculations.

Off-centering of the disk in the halo potential and the kinematic lopsidedness in the dwarf irregular galaxy WLM

In this work, to investigate the dynamical nature of the kinematic asymmetry in the isolated gas-rich dwarf irregular galaxy W LM in the Local Group, we consider that the dark matter halo and the disk do not have the same center of mass (i.e., the disk lies off-center in the potential of the extended dark matter halo), which is one of the possible physical explanations for the kinematic lopsidedness. To do so, we generate a lopsided halo potential by considering two dark matter mass density models, ISO and Burkert, and we add up the contribution to the rotation curve of a perturbation term [Formula: see text] in the gravitational potential, which arises from the offset between the disk and the dark matter halo. We show that such an m = 1 perturbation improves the rotation curve modeling when compared to a non-perturbed potential and the shape of the HI gas rotation curves is fitted better in the approaching side if the perturbation term in the halo potential is taken into account for this galaxy dynamics. In fact, displacing the disk center by 0.1 kpc from the halo center is sufficient to provide such an improvement in modeling the rotation curve.

Deeply Buried Nuclei in the Infrared-luminous Galaxies NGC 4418 and Arp 220. II. Line Forests at λ = 1.4–0.4 mm and Circumnuclear Gas Observed with ALMA

Abstract We present the line observations in our Atacama Millimeter-Submillimeter Array imaging spectral scan toward three deeply buried nuclei in NGC 4418 and Arp 220. We cover 67 GHz in f rest = 215–697 GHz at about 0.″2 (30, 80 pc) resolution. All the nuclei show dense line forests; we report our initial line identification using 55 species. The line velocities generally indicate gas rotation around each nucleus, tracing nuclear disks of ∼100 pc in size. We confirmed the counter-rotation of the nuclear disks in Arp 220 and that of the nuclear disk and the galactic disk in NGC 4418. While the brightest lines exceed 100 K, most of the major lines and many 13C isotopologues show absorption against even brighter continuum cores of the nuclei. The lines with higher upper-level energies, including those from vibrationally excited molecules, tend to arise from smaller areas, indicating radially varying conditions in these nuclei. The outflows from the two Arp 220 nuclei cause blueshifted line absorption below the continuum level. The absorption mostly has small spatial offsets from the continuum peaks to indicate the outflow orientations. The bipolar outflow from the western nucleus is also imaged in multiple emission lines, showing the extent of ∼1″ (400 pc). Redshifted line absorption against the nucleus of NGC 4418 indicates either an inward gas motion or a small collimated outflow slanted to the nuclear disk. We also resolved some previous confusions due to line blending and misidentification.

Molecular gas kinematics in the nuclear region of nearby Seyfert galaxies with ALMA

Context. The study of the distribution, morphology, and kinematics of cold molecular gas in the nuclear and circumnuclear regions of active galactic nuclei (AGNs) helps to characterise and hence to quantify the impact of the AGNs on the host galaxy over its lifetime. Aims. We present the analysis of the molecular gas in the nuclear regions of three Seyfert galaxies, NGC 4968, NGC 4845, and MCG-06-30-15, using Atacama Large sub-Millimetre Array (ALMA) observations of the CO(2−1) emission line. The aim is to determine the kinematics of the gas in the central (∼1 kpc) region and thereby to probe nuclear fueling and feedback of AGNs. Methods. We used two different softwares, namely the 3D-Based Analysis of Rotating Object via Line Observations and DiskFit, to model the kinematics of the gas in the molecular disc, and thereby to determine the gas rotation and any kinematical perturbations. Results. Circular motions dominate the kinematics of the molecular gas in the central discs, mainly in NGC 4845 and MCG-06-30-15; however there is clear evidence of non-circular motions in the central (∼1 kpc) region of NGC 4845 and NGC 4968. The strongest non-circular motion is detected in the inner disc of NGC 4968, mainly along the minor kinematic axis, with a velocity ∼115 km s−1. Of all DiskFit models, the bisymmetric model is found to give the best fit for NGC 4968 and NGC 4845, indicating that the observed non-circular motions in the inner disc of these galaxies could result from the nuclear barred structure, where the gas streams in elliptical orbits aligned along the bar. If the dynamics of NGC 4968 is modelled as a corotation pattern just outside of the bar, the bar pattern speed becomes Ωb = 52 km s−1 kpc−1; the corotation is set at 3.5 kpc; and the inner Lindblad resonance (ILR) ring is R = 300 pc, corresponding to the CO emission ring. In the NGC 4968 galaxy, the torques exerted on the gas by the bar are positive in the centre, within the gas nuclear ring, and negative outside. This shows that the gas is transiently trapped in the ILR. The comparison of the CO intensity maps with the map of the cold dust emission shows an absence of CO in the centre of NGC 4968; also the dust distribution and CO emission in and around the centre of NGC 4845 have similar extensions. The 1.2 mm ALMA continuum is peaked and compact in NGC 4968 and MCG-06-30-15, but their CO(2−1) emissions have extended distributions. Allowing the CO-to-H2 conversion factor αCO between 0.8 and 3.2, which is typical of nearby galaxies of the same type, the molecular mass M(H2) is estimated to be ∼3 − 12 × 107 M⊙ (NGC 4968), ∼9 − 36 × 107 M⊙ (NGC 4845), and ∼1 − 4 × 107 M⊙ (MCG-06-30-15). Conclusions. We conclude that the observed non-circular motions in the molecular disc of NGC 4968 and likely those seen in NGC 4845 are due to the presence of the bar in the nuclear region. We discuss the possibility that the observed pattern in the kinematics might be a consequence of the presence of AGNs, and this might be the case for NGC 4845. At the current spectral and spatial resolution and sensitivity, we cannot claim any strong evidence in these sources of the long sought feedback or feeding effect resulting from the presence of AGNs.

On the thermal instability of supercavitating liquid jet surrounded by coaxial rotary gas

Abstract Based on the jet stability theory, under the conditions of gas rotation, fluid compressibility and supercavitation, this paper gives the mathematical model describing the thermal instability of supercavitating liquid jet surrounded by a coaxial rotary gas, and the corresponding numerical method for solving the mathematical model is proposed and verified by the data in reference. Then, this paper analyzes the effects of gas–liquid temperature differences and temperature gradients on jet instability, and studies the thermal stability of supercavitating jet. The results show that the maximum disturbance growth rate, the dominant frequency and the maximum disturbance wave numbers increase linearly with the increase of gas–liquid temperature differences. The existence of temperature gradient inside the jet makes the effects of temperature differences on jet instability more obvious. The temperature gradient will inhibit the effect of supercavitation on jet instability, while gas–liquid temperature difference will promote the effect of supercavitation on jet instability.

Insights into the causes and controlling strategies of gas temperature deviation in a 660 MW tangentially fired tower-type boiler

• Experiment & simulation on thermal deviation are performed in a tower-type boiler. • Four upper furnace structures are studied to fully reveal the deviation causes. • Properly SOFA horizontal angle of 34–45° is recommended. • SOFA velocity offset with 1.2 of left/right ratio is recommended. • Offsetting SOFA velocity is successfully applied without adverse effects. Gas temperature deviation is a common problem for tangentially fired boilers, affecting the boiler operation safety and the boiler generation efficiency. The gas temperature deviation in the tangentially fired π-type boilers has been well studied. However, the gas temperature deviation in the tangentially fired tower-type boilers has yet to be fully understood. This paper develops insights into the causes and controlling strategies of gas temperature deviation in a 660 MW tangentially fired tower-type boiler with obvious steam temperature deviation by experiment and simulation. Firstly, four upper furnace structures are established to fully reveal the causes of gas temperature deviation. The gas temperature deviation is mainly caused by the flue gas rotation, the heating tubes division, and the suction effect of the induced draft fan. More evident recirculation is observed near the right side than the left side in the platen heater region, resulting in that the flue gas deflects to the left side, and the left side region presents higher temperature. Furthermore, the controlling strategies of gas temperature deviation are studied comprehensively by adjusting SOFA (Separated Over-fire Air) horizontal angle and setting SOFA left–right-side velocity offset. Properly SOFA horizontal angle or enhancing the left-side SOFA velocity may effectively reduce the gas temperature deviation. 34–45° for the SOFA horizontal angle and 1.2 for the SOFA left–right-side velocity ratio are recommended. In the actual operation, offsetting the SOFA left–right-side velocity ( i. e. SOFA air damper opening degree: left side—80% and right side—50%) is successfully applied to reduce the re-heated steam temperature deviation from 18 K to 1 K without bringing adverse effects under the low load. These deep insights may provide useful information to control the steam temperature deviation in the platen heater zone.

The nuclear stellar disc of the Milky Way: A dynamically cool and metal-rich component possibly formed from the central molecular zone

Context. The nuclear stellar disc (NSD) is, together with the nuclear star cluster (NSC) and the central massive black hole, one of the main components in the central parts of our Milky Way. However, until recently, only a few studies of the stellar content of the NSD have been obtained owing to extreme extinction and stellar crowding. Aims. We study the kinematics and global metallicities of the NSD based on the observations of K/M giant stars via a dedicated KMOS (VLT, ESO) spectroscopic survey. Methods. We traced radial velocities and metallicities, which were derived based on spectral indices (Na I and CO) along the NSD, and compared those with a Galactic bulge sample of APOGEE (DR16) and data from the NSC. Results. We find that the metallicity distribution function and the fraction of metal-rich and metal-poor stars in the NSD are different from the corresponding distributions and ratios of the NSC and the Galactic bulge. By tracing the velocity dispersion as a function of metallicity, we clearly see that the NSD is kinematically cool and that the velocity dispersion decreases with increasing metallicity contrary to the inner bulge sample of APOGEE (|b|< 4°). Using molecular gas tracers (H2CO, CO(4−3)) of the central molecular zone (CMZ), we find an astonishing agreement between the gas rotation and the rotation of the metal-rich population. This agreement indicates that the metal-rich stars could have formed from gas in the CMZ. On the other hand, the metal-poor stars show a much slower rotation profile with signs of counter-rotation, thereby indicating that these stars have a different origin. Conclusions. Coupling kinematics with global metallicities, our results demonstrate that the NSD is chemically and kinematically distinct with respect to the inner bulge, which indicates a different formation scenario.

Spectral Observations of Superthin Galaxies

Abstract We conduct spectral observations of 138 superthin galaxies (STGs) with high radial-to-vertical stellar disk scale ratios with the Dual Imaging Spectrograph on the 3.5 m telescope at the Apache Point Observatory (APO) to obtain the ionized gas rotation curves with R ∼5000 resolution. We also performed near-infrared (NIR) H and Ks photometry for 18 galaxies with the NICFPS camera on the 3.5 m telescope. The spectra, the NIR photometry, and published optical and NIR photometry are used for modeling that utilizes the thickness of the stellar disk and rotation curves simultaneously. The projection and dust extinction effects are taken into account. We evaluate eight models that differ in their free parameters and constraints. As a result, we estimated the masses and scale lengths of the galactic dark halos. We find systematic differences between the properties of our red and blue STGs. The blue STGs have a large fraction of dynamically underevolved galaxies whose vertical velocity dispersion is low in both gas and stellar disks. The dark halo-to-disk scale ratio is shorter in the red STGs than in the blue ones, but in a majority of all STGs, this ratio is under 2. The optical color (r − i) of the STGs correlates with their rotation curve maximum, vertical velocity dispersion in stellar disks, and mass of the dark halo. We conclude that there is a threshold central surface density of 50 M ⊙ pc−2 below which we do not observe very thin, rotationally supported galactic disks.

HI detection of J030417.78+002827.4 by the Five-hundred-meter Aperture Spherical Radio Telescope

We present the first HI 21 cm spectroscopy detection of J030417.78+002827.4, which is an active galactic nucleus (AGN) with an intermediate-mass black hole (IMBH) in the center. The observations were carried out with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) last year. We relied on the ON-OFF observing approach with the 19-beam receiver covering 1.05 – 1.45 GHz. Within a total integration time of about 20 min, the root mean square (RMS) of our data reaches 1.2 mJy beam−1, at a velocity resolution of 1.6 kms. Radio frequency interference (RFI) is checked and excluded during the data analysis. The detected HI spectroscopy shows a dual-horned profile with a line width of 223.5 kms, indicating gas rotation around this AGN. The redshift of this galaxy derived from our HI observation is 0.0447. We calculate the atomic gas mass by the integrated flux of the HI emission line. The total gas mass in this galaxy is estimated to be 1.8 × 1010 M ⊙. We find the fraction of gas-to-stellar mass ratio in J030417.78+002827.4 is more than 50%. This ratio is much higher than the typical value found in other AGNs with supermassive black holes (SMBHs), and is comparable to some star-forming galaxies recently observed by FAST.

Thermal deviation analysis of high-temperature reheater for single-tangential π type boiler

• The thermal deviation adjusting experiments of a 660 MW ultra-supercritical boiler were carried out. • The grid distribution of radiation intensity for particles at the high-temperature reheater area was measured by radiation spectroscopy. • Thermal deviation analysis of high-temperature reheater were presented. • A new type principle of reforming combustion system was proposed. For some π type boilers with four-corner tangential and deep air staged low nitrogen combustion technology, under full load condition, the steam temperature deviation for both sides of reheater outlet can reach as high as 15 °C. The left and right cross arrangement of steam between two stage reheaters increases the steam temperature deviation at the outlet, and the large amount input of desuperheating water makes the economic efficiency of the unit decrease. The thermal deviation adjusting experiments of a 660 MW ultra-supercritical boiler were carried out by adjusting the level and up-and-down swing angle of the separated over-fire air nozzle, and the grid distribution of radiation intensity for particles at the high-temperature reheater area was measured by radiation spectroscopy. The results show that there exists strong visible radiation in this area. Under the 600 MW-load condition, the radiation heat transfer of particle accounts for 25.95% of the total heat absorption of the high-temperature superheater and particle combustion still exists, whose combustion share accounts for about 1.83% of the received carbon content of coal. The particle temperature and emittance data fitted from the Planck's law indicate that the high-temperature particles are enriched at single side due to the inertial effect of residual rotation of flue gas. The residual rotation momentum of the separated over-fire air is insufficient to balance the temperature rise of both sides of the low-temperature reheater. Therefore, a new type principle of reforming combustion system was proposed, which changes a five-layer Separated Over-fire Air (SOFA) nozzle to two-section of six-layer SOFA nozzle to mitigate the combustion delay of pulverized coal particles and sets the wall-type tangent circle arrangement of the upper separated over-fire air nozzle to improve the residual rotation momentum of flue gas.

A Comparative Study on Fault Detection Methods for Gas Turbine Combustion Systems

As one of the core components of gas turbines, the combustion system operates in a high-temperature and high-pressure adverse environment, which makes it extremely prone to faults and catastrophic accidents. Therefore, it is necessary to monitor the combustion system to detect in a timely way whether its performance has deteriorated, to improve the safety and economy of gas turbine operation. However, the combustor outlet temperature is so high that conventional sensors cannot work in such a harsh environment for a long time. In practical application, temperature thermocouples distributed at the turbine outlet are used to monitor the exhaust gas temperature (EGT) to indirectly monitor the performance of the combustion system, but, the EGT is not only affected by faults but also influenced by many interference factors, such as ambient conditions, operating conditions, rotation and mixing of uneven hot gas, performance degradation of compressor, etc., which will reduce the sensitivity and reliability of fault detection. For this reason, many scholars have devoted themselves to the research of combustion system fault detection and proposed many excellent methods. However, few studies have compared these methods. This paper will introduce the main methods of combustion system fault detection and select current mainstream methods for analysis. And a circumferential temperature distribution model of gas turbine is established to simulate the EGT profile when a fault is coupled with interference factors, then use the simulation data to compare the detection results of selected methods. Besides, the comparison results are verified by the actual operation data of a gas turbine. Finally, through comparative research and mechanism analysis, the study points out a more suitable method for gas turbine combustion system fault detection and proposes possible development directions.

From dwarf galaxies to galaxy clusters: Self-Interacting Dark Matter over 7 orders of magnitude in halo mass

In this paper we study the density profiles of self-interacting dark matter (SIDM) haloes spanning the full observable mass range, from dwarf galaxies to galaxy clusters. Using realistic simulations that model the baryonic physics relevant for galaxy formation, we compare the density profiles of haloes simulated with either SIDM or cold and collisionless dark matter (CDM) to those inferred from observations of stellar velocity dispersion, gas rotation curves, weak and strong gravitational lensing, and/or X-ray maps. We make our comparison in terms of the maximal surface density of haloes, circumventing the need for semi-analytic or parametric models for dark matter density profiles. We find that the maximal surface density as a function of halo mass is well reproduced by CDM simulations that include baryons, while for SIDM with a velocity-independent cross-section of 1 cm2/g, the simulated galaxy clusters have mean maximal surface densities that are below those of observed systems by an amount greater than the standard deviation of the observed maximal surface density at fixed mass. For less massive systems both CDM and SIDM agree with the observation equally well.

Morphological and Rotation Structures of Circumgalactic Mg ii Gas in the EAGLE Simulation and the Dependence on Galaxy Properties

Abstract Low-ionization-state Mg ii gas has been extensively studied in quasar sightline observations to understand the cool, ∼104 K gas in the circumgalactic medium. Motivated by recent observations showing that the Mg ii gas around low-redshift galaxies has significant angular momentum, we use the high-resolution EAGLE cosmological simulation to analyze the morphological and rotation structures of the z ≈ 0.3 circumgalactic Mg ii gas and examine how they change with the host galaxy properties. Around star-forming galaxies, we find that the Mg ii gas has an axisymmetric instead of a spherical distribution, and the axis of symmetry aligns with that of the Mg ii gas rotation. A similar rotating structure is less commonly found in the small sample of simulated quiescent galaxies. We also examine how often Mg ii gas around galaxies selected using a line-of-sight velocity cut includes gas physically outside of the virial radius (r vir). For example, we show that at an impact parameter of 100 pkpc, a ±500 km s−1 velocity cut around galaxies with stellar masses of 109–109.5 M ⊙ (1010–1010.5 M ⊙) selects Mg ii gas beyond the virial radius 80% (6%) of the time. Because observers typically select Mg ii gas around target galaxies using such a velocity cut, we discuss how this issue affects the study of circumgalactic Mg ii gas properties, including the detection of corotation. While the corotating Mg ii gas generally extends beyond 0.5r vir, the Mg ii gas outside of the virial radius contaminates the corotation signal and makes observers less likely to conclude that gas at large impact parameters (e.g., ≳0.25r vir) is corotating.

Joint gas and stellar dynamical models of WLM: an isolated dwarf galaxy within a cored, prolate DM halo

ABSTRACT We present multitracer dynamical models of the low-mass (M* ∼ 107), isolated dwarf irregular galaxy WLM in order to simultaneously constrain the inner slope of the dark matter (DM) halo density profile (γ) and flattening (qDM), and the stellar orbital anisotropy (βz, βr). For the first time, we show how jointly constraining the mass distribution from the H i gas rotation curve and solving the Jeans equations with discrete stellar kinematics lead to a factor of ∼2 reduction in the uncertainties on γ. The mass-anisotropy degeneracy is also partially broken, leading to reductions on uncertainty by ${\sim} 30{{\ \rm per\ cent}}$ on Mvir (and ${\sim} 70{{\ \rm per\ cent}}$ at the half-light radius) and ${\sim} 25{{\ \rm per\ cent}}$ on anisotropy. Our inferred value of γ = 0.3 ± 0.1 is robust to the halo geometry, and in excellent agreement with predictions of stellar feedback-driven DM core creation. The derived prolate geometry of the DM halo with qDM = 2 ± 1 is consistent with Lambda cold dark matter simulations of dwarf galaxy haloes. While self-interacting DM (SIDM) models with σ/mX ∼ 0.6 can reproduce this cored DM profile, the interaction events may sphericalize the halo. The simultaneously cored and prolate DM halo may therefore present a challenge for SIDM. Finally, we find that the radial profile of stellar anisotropy in WLM (βr) follows a nearly identical trend of increasing tangential anisotropy to the classical dwarf spheroidals, Fornax and Sculptor. Given WLM’s orbital history, this result may call into question whether such anisotropy is a consequence of tidal stripping in only one pericentric passage or if it instead is a feature of the largely self-similar formation and evolutionary pathways for some dwarf galaxies.

Asymmetric drift of Andromeda analogues in the IllustrisTNG simulation

ABSTRACT We analyse the kinematics as a function of stellar age for Andromeda (M31) mass analogues from the IllustrisTNG cosmological simulation. We divide the star particles into four age groups: <1, 1–5, 5–10, and >10 Gyr, and compare the kinematics of these groups to that of the neutral gas cells. We calculate rotation curves for the stellar and gaseous components of each analogue from 2 to 20 kpc from the centre of mass. We find that the lag, or asymmetric drift (AD), between the gas rotation curve and the stellar rotation curve on average increases with stellar age. This finding is consistent with observational measurements of AD in the disc of the Andromeda galaxy. When the M31 analogues are separated into groups based on merger history, we find that there is a difference in the AD of the analogues that have had a 4:1 merger the last 4, 8, or 12 Gyr compared to analogues that have not experienced a 4:1 merger in the same time frame. The subset of analogues that have had a 4:1 merger within the last 4 Gyr are also similar to AD measurements of stars in M31’s disc, providing evidence that M31 may in fact have recently merged with a galaxy nearly one-fourth of its mass. Further work using high-resolution zoom-in simulations is required to explore the contribution of internal heating to AD.

Measuring dynamical masses from gas kinematics in simulated high-redshift galaxies

ABSTRACT Advances in instrumentation have recently extended detailed measurements of gas kinematics to large samples of high-redshift galaxies. Relative to most nearby, thin disc galaxies, in which gas rotation accurately traces the gravitational potential, the interstellar medium (ISM) of $z$ ≳ 1 galaxies is typically more dynamic and exhibits elevated turbulence. If not properly modelled, these effects can strongly bias dynamical mass measurements. We use high-resolution FIRE-2 cosmological zoom-in simulations to analyse the physical effects that must be considered to correctly infer dynamical masses from gas kinematics. Our analysis covers a range of galaxy properties from low-redshift Milky-Way-mass galaxies to massive high-redshift galaxies (M⋆ > 1011 M⊙ at $z$ = 1). Selecting only snapshots where a disc is present, we calculate the rotational profile $\bar{v}_\phi (r)$ of the cool ($10^{3.5}\,\lt {\it T}\lt 10^{4.5}~\rm {K}$) gas and compare it to the circular velocity $v_{\rm c}=\sqrt{GM_{\rm enc}/r}$. In the simulated galaxies, the gas rotation traces the circular velocity at intermediate radii, but the two quantities diverge significantly in the centre and in the outer disc. Our simulations appear to over-predict observed rotational velocities in the centres of massive galaxies (likely from a lack of black hole feedback), so we focus on larger radii. Gradients in the turbulent pressure at these radii can provide additional radial support and bias dynamical mass measurements low by up to 40 per cent. In both the interior and exterior, the gas’ motion can be significantly non-circular due to e.g. bars, satellites, and inflows/outflows. We discuss the accuracy of commonly used analytic models for pressure gradients (or ‘asymmetric drift’) in the ISM of high-redshift galaxies.

Magnetic Field Structure of Orion Source I

Abstract We observed polarization of the SiO rotational transitions from Orion Source I (SrcI) to probe the magnetic field in bipolar outflows from this high-mass protostar. Both 43 GHz J = 1–0 and 86 GHz J = 2–1 lines were mapped with ∼20 au resolution, using the Very Large Array (VLA) and Atacama Large Millimeter/Submillimeter Array (ALMA), respectively. The 28SiO transitions in the ground vibrational state are a mixture of thermal and maser emission. Comparison of the polarization position angles in the J = 1–0 and J = 2–1 transitions allows us to set an upper limit on possible Faraday rotation of 104 rad m−2, which would twist the J = 2–1 position angles typically by less than 10°. The smooth, systematic polarization structure in the outflow lobes suggests a well-ordered magnetic field on scales of a few hundred au. The uniformity of the polarization suggests a field strength of ∼30 mG. It is strong enough to shape the bipolar outflow and possibly lead to sub-Keplerian rotation of gas at the base of the outflow. The strikingly high fractional linear polarizations of 80%–90% in the 28SiO v = 0 masers require anisotropic pumping. We measured circular polarizations of 60% toward the strongest maser feature in the v = 0 J = 1–0 peak. Anisotropic resonant scattering is likely to be responsible for this circular polarization. We also present maps of the 29SiO v = 0 J = 2–1 maser and several other SiO transitions at higher vibrational levels and isotopologues.

Decoupling the rotation of stars and gas – II. The link between black hole activity and simulated IFU kinematics in IllustrisTNG

ABSTRACT We study the relationship between supermassive black hole (BH) feedback, BH luminosity, and the kinematics of stars and gas for galaxies in IllustrisTNG. We use galaxies with mock MaNGA observations to identify kinematic misalignment at z = 0 (difference in rotation of stars and gas), for which we follow the evolutionary history of BH activity and gas properties over the last 8 Gyr. Misaligned low-mass galaxies ($\mathrm{\mathit{ M}_{stel} \lt 10^{10.2}\, \mathrm{M}_{\odot }}$) typically have boosted BH luminosity and BH growth, and have had more energy injected by BHs into the gas over the last 8 Gyr in comparison to low-mass aligned galaxies. These properties likely lead to outflows and gas removal, in agreement with active low mass galaxies in observations. Splitting on BH luminosity at z = 0 produces consistent distributions of kinematic misalignment at z = 0; however, splitting on the maximum BH luminosity over the last 8 Gyr produces statistically significant different distributions. While instantaneous correlation at z = 0 is difficult due to misalignment persisting on longer time-scales, the relationship between BH activity and misalignment is clear. High-mass quenched galaxies ($\mathrm{\mathit{ M}_{stel} \gt 10^{10.2}\, \mathrm{M}_{\odot }}$) with misalignment typically have similar BH luminosities, show lower gas fractions, and have typically lower gas phase metallicity over the last 8 Gyr in comparison to the high mass aligned.

The efficiency of dust trapping in ringed protoplanetary discs

ABSTRACT When imaged at high resolution, many protoplanetary discs show gaps and rings in their dust sub-mm continuum emission profile. These structures are widely considered to originate from local maxima in the gas pressure profile. The properties of the underlying gas structures are however unknown. In this paper, we present a method to measure the dust–gas coupling α/St and the width of the gas pressure bumps affecting the dust distribution, applying high-precision techniques to extract the gas rotation curve from emission line data cubes. As a proof of concept, we then apply the method to two discs with prominent substructure, HD 163296 and AS 209. We find that in all cases the gas structures are larger than in the dust, confirming that the rings are pressure traps. Although the grains are sufficiently decoupled from the gas to be radially concentrated, we find that the degree of coupling of the dust is relatively good (α/St ∼ 0.1). We can therefore reject scenarios in which the disc turbulence is very low and the dust has grown significantly. If we further assume that the dust grain sizes are set by turbulent fragmentation, we find high values of the α turbulent parameter (α ∼ 10−2). Alternatively, solutions with smaller turbulence are still compatible with our analysis if another process is limiting grain growth. For HD 163296, recent measurements of the disc mass suggest that this is the case if the grain size is 1 mm. Future constraints on the dust spectral indices will help to discriminate between the two alternatives.

Decoupling the rotation of stars and gas – I. The relationship with morphology and halo spin

ABSTRACT We use a combination of data from the MaNGA survey and MaNGA-like observations in IllustrisTNG100 to determine the prevalence of misalignment between the rotational axes of stars and gas. This census paper outlines the typical characteristics of misaligned galaxies in both observations and simulations to determine their fundamental relationship with morphology and angular momentum. We present a sample of ∼4500 galaxies from MaNGA with kinematic classifications which we use to demonstrate that the prevalence of misalignment is strongly dependent on morphology. The misaligned fraction sharply increases going to earlier morphologies (28 ± 3 per cent of 301 early-type galaxies, 10 ± 1 per cent of 677 lenticulars, and 5.4 ± 0.6 per cent of 1634 pure late-type galaxies). For early-types, aligned galaxies are less massive than the misaligned sample whereas this trend reverses for lenticulars and pure late-types. We also find that decoupling depends on group membership for early-types with centrals more likely to be decoupled than satellites. We demonstrate that misaligned galaxies have similar stellar angular momentum to galaxies without gas rotation, much lower than aligned galaxies. Misaligned galaxies also have a lower gas mass than the aligned, indicative that gas loss is a crucial step in decoupling star–gas rotation. Through comparison to a mock MaNGA sample, we find that the strong trends with morphology and angular momentum hold true in IllustrisTNG100. We demonstrate that the lowered angular momentum is, however, not a transient property and that the likelihood of star–gas misalignment at $z$ = 0 is correlated with the spin of the dark matter halo going back to $z$ = 1.