Stellar Velocity Field Research Articles

Different Influence of Gas Accretion on the Evolution of Star-forming and Non-star-forming Galaxies

Using integral field spectroscopic data from the Mapping Nearby Galaxies at Apache Point Observatory survey, we investigate the spatially resolved properties and empirical relations of a star-forming galaxy and a non-star-forming galaxy hosting counterrotating stellar disks (CRDs). The DESI g, r, z color images reveal no evidence of merger remnants in either galaxy, suggesting that gas accretion fuels the formation of CRDs. Based on the visible counterrotation in the stellar velocity field, we can fit a spatial boundary to distinguish the inner and outer regions dominated by two stellar disks in each galaxy. In the inner region of the star-forming CRDs, stars are corotating with ionized gas, and the stellar population is younger. Comparison of the star-forming main-sequence relations between the inner and outer regions reveals enhanced star formation in the inner region. Given the abundant preexisting gas in the star-forming galaxy, collisions between preexisting and external gas efficiently consume angular momentum, triggering star formation in the inner region. Conversely, in the outer region of the non-star-forming CRDs, stars are corotating with ionized gas, and the stellar population is younger. Comparison of the stellar mass–metallicity relations between the inner and outer regions indicates enriched gas-phase metallicity in the outer region. Considering the less abundant preexisting gas in the non-star-forming galaxy, external gas could preserve angular momentum, fueling star formation in the outer region. Overall, gas accretion exhibits different influences on the evolution of star-forming and non-star-forming galaxies.

A new kinematic model of the Galaxy: analysis of the stellar velocity field from Gaia Data Release 3

ABSTRACT This work presents the results of a kinematic analysis of the Galaxy that uses a new model as applied to the newest available Gaia data. We carry out the Taylor decomposition of the velocity field up to second order for 18 million high luminosity stars (i.e. OBAF-type stars, giants, and subgiants) from the Gaia DR3 data. We determine the components of mean stellar velocities and their first and second partial derivatives (relative to cylindrical coordinates) for more than 28 thousand points in the plane of our Galaxy. We estimate Oort’s constants A, B, C, and K and other kinematics parameters and map them as a function of Galactocentric coordinates. The values found confirm the results of our previous works and are in excellent agreement with those obtained by other authors in the solar neighbourhood. In addition, the introduction of second order partial derivatives of the stellar velocity field allows us to determine the values of the vertical gradient of the Galaxy azimuthal, radial, and vertical velocities. Also, we determine the mean of the Galaxy rotation curve for Galactocentric distances from 4 to 18 kpc by averaging Galactic azimuths in the range −30° < θ < + 30° about the direction Galactic Centre – Sun – Galactic anticentre. Maps of the velocity components and of their partial derivatives with respect to coordinates within 10 kpc of the Sun reveal complex substructures, which provide clear evidence of non-axisymmetric features of the Galaxy. Finally, we show evidence of differences in the Northern and Southern hemispheres stellar velocity fields.

AGN feedback in action in the molecular gas ring of the Seyfert galaxy NGC 7172

We present new ALMA observations of the CO(3−2) transition and associated 854 μm continuum at 0.06 − 0.3″ resolution, together with new VLT/SINFONI observations of NGC 7172. This is a luminous (bolometric luminosity of ≃1044 erg s−1) Seyfert galaxy that belongs to the Galaxy Activity, Torus, and Outflow Survey (GATOS). The ALMA CO(3−2) observations reveal the presence of a highly inclined cold molecular gas ring with an approximate radius of 3 − 4″ ≃ 540 − 720 pc, which is likely associated with an inner Lindblad resonance of a putative stellar bar. There are noncircular motions in the VLT/SINFONI [Si VI]λ1.96 μm and H2 at 2.12 μm, and ALMA CO(3−2) velocity fields. After subtracting the stellar velocity field, we detected [Si VI] blueshifted velocities of a few hundred km s−1 to the south of the active galactic nucleus (AGN) position. They trace outflowing ionized gas outside the plane of the galaxy and out to projected distances of ≃200 pc. The CO(3−2) position-velocity diagram along the kinematic minor axis displays noncircular motions with observed velocities of up to ∼150 km s−1. Assuming that these are taking place in the disk of the galaxy, the observed velocity signs imply that the molecular gas ring is not only rotating but also outflowing. We derived an integrated cold molecular gas mass outflow rate of ∼40 M⊙ yr−1 for the ring. Using the ALMA 854 μm extended emission map, we resolved a 32 pc radius torus with a gas mass of 8 × 105 M⊙. These torus properties are similar to other Seyfert galaxies in the GATOS sample. We measured a decreased cold molecular gas concentration in the nuclear-torus region relative to the circumnuclear region when compared to other less luminous Seyfert galaxies. We conclude that the effects of AGN feedback in NGC 7172, which are likely caused by the AGN wind and/or the moderate luminosity radio jet, are seen as a large-scale outflowing molecular gas ring and accompanying redistribution of molecular gas in the nuclear regions.

The State of the Molecular Gas in Post-starburst Galaxies

The molecular gas in galaxies traces both the fuel for star formation and the processes that can enhance or suppress star formation. Observations of the molecular gas state can thus point to when and why galaxies stop forming stars. In this study, we present Atacama Large Millimeter/submillimeter Array observations of the molecular gas in galaxies evolving through the post-starburst phase. These galaxies have low current star formation rates (SFRs), regardless of the SFR tracer used, with recent starbursts ending within the last 600 Myr. We present CO (3–2) observations for three post-starburst galaxies, and dense gas HCN/HCO+/HNC (1–0) observations for six (four new) post-starburst galaxies. The post-starbursts have low excitation traced by the CO spectral-line energy distribution up to CO (3–2), more similar to early-type than starburst galaxies. The low excitation indicates that lower density rather than high temperatures may suppress star formation during the post-starburst phase. One galaxy displays a blueshifted outflow traced by CO (3–2). MaNGA observations show that the ionized gas velocity is disturbed relative to the stellar velocity field, with a blueshifted component aligned with the molecular gas outflow, suggestive of a multiphase outflow. Low ratios of HCO+/CO, indicating low fractions of dense molecular gas relative to the total molecular gas, are seen throughout post-starburst phase, except for the youngest post-starburst galaxy considered here. These observations indicate that the impact of any feedback or quenching processes may be limited to low excitation and weak outflows in the cold molecular gas during the post-starburst phase.

Mapping the kinematic parameters of the Galaxy from the Gaia EDR3 red giants and sub-giants

ABSTRACT We present the results of a kinematic analysis of red giants and sub-giants whose centroids are in the plane of our Galaxy. For this, the positions, parallaxes, proper motions, and radial velocities of these stars from the Gaia EDR3 catalogue were used. We applied two approaches to obtain kinematic parameters. The first approach – solving the equations of the Ogorodnikov–Milne model with respect to 12 unknowns – is generally accepted, but has a number of disadvantages. The second approach applied by us is to find the Galactocentric centroid velocity components and their partial derivatives with respect to coordinates from the solution of formal equations for the scalar stellar velocity field. To calculate the kinematic parameters by the methods mentioned above, same stellar samples were used. From these samples spherical regions with a radius of 1 kpc were selected, the centers of which were located strictly in the Galactic mid-plane at the nodes of the coordinate grid (xgal, ygal) of a rectangular Galactocentric coordinate system with step 100 pc. The investigated region of the Galaxy is located approximately in coordinate ranges 120° < θ < 240°, 0 kpc <R < 16 kpc, –1 kpc <z <1 kpc. We show the behaviour of kinematic parameters depending on the Galactocentric coordinates. The kinematic parameters as a function of Galactic coordinates were derived for the first time. Also, for the first time, the parameters ∂VR/∂θ and ∂Vθ/∂θ were derived.

Gaussian process model for the local stellar velocity field from Gaia data release 2

ABSTRACT We model the local stellar velocity field using position and velocity measurements for 4M stars from the second data release of Gaia. We determine the components of the mean or bulk velocity in $\sim 27\, 000$ spatially defined bins. Our assumption is that these quantities constitute a Gaussian process where the correlation between the bulk velocity at different locations is described by a simple covariance function or kernel. We use a sparse Gaussian process algorithm based on inducing points to construct a non-parametric, smooth, and differentiable model for the underlying mean stellar velocity field. We estimate the Oort constants A, B, C, and K and find values in excellent agreement with previous results. Maps of the velocity field within $2\, {\rm kpc}$ of the Sun reveal complicated substructures, which provide clear evidence that the local disc is in a state of disequilibrium. We present the first three-dimensional map of the divergence of the stellar velocity field and identify regions of the disc that may be undergoing compression and rarefaction.

Gas inflows in the polar ring of NGC 4111: the birth of an AGN

ABSTRACT We have used Hubble Space Telescope (HST) images, SAURON Integral Field Spectroscopy (IFS), and adaptative optics assisted Gemini NIFS near-infrared K-band IFS to map the stellar and gas distribution, excitation and kinematics of the inner few kpc of the nearby edge-on S0 galaxy NGC 4111. The HST images map its ≈450 pc diameter dusty polar ring, with an estimated gas mass ≥107 M⊙. The NIFS data cube maps the inner 110 pc radius at ≈7 pc spatial resolution, revealing a ≈220 pc diameter polar ring in hot (2267 ± 166 K) molecular H2 1–0 S(1) gas embedded in the polar ring. The stellar velocity field shows disc-dominated kinematics along the galaxy plane both in the SAURON large scale and in the NIFS nuclear-scale data. The large-scale [O iii] λ5007 Å velocity field shows a superposition of two disc kinematics: one similar to that of the stars and another along the polar ring, showing non-circular motions that seem to connect with the velocity field of the nuclear H2 ring, whose kinematics indicate accelerated inflow to the nucleus. The estimated mass inflow rate is enough not only to feed an active galactic nucleus (AGN) but also to trigger circumnuclear star formation in the near future. We propose a scenario in which gas from the polar ring, which probably originated from the capture of a dwarf galaxy, is moving inwards and triggering an AGN, as supported by the local X-ray emission, which seems to be the source of the H2 1–0 S(1) excitation. The fact that we see neither near-UV nor Br γ emission suggests that the nascent AGN is still deeply buried under the optically thick dust of the polar ring.

Different Formation Scenarios for Counterrotating Stellar Disks in Nearby Galaxies

Abstract Using the integral field unit data from the Mapping Nearby Galaxies at Apache Point Observatory survey, we select a sample of 101 galaxies with counterrotating stellar disks and regularly rotating ionized gas disks. We classify the 101 galaxies into four types based on the features of their stellar velocity fields. The relative fractions and stellar population age radial gradients of the four types are different in the blue cloud, green valley, and red sequence populations. We suggest different formation scenarios for counterrotating stellar disks; the key factors in the formation of counterrotating stellar disks include (1) the abundance of preexisting gas in the progenitor and (2) the efficiency in angular momentum consumption.

Quantifying the Stellar Halo's Response to the LMC's Infall with Spherical Harmonics

Abstract The vast majority of the mass in the Milky Way (MW) is in dark matter (DM); we therefore cannot directly observe the MW mass distribution and have to use tracer populations in order to infer properties of the MW DM halo. However, MW halo tracers do not only feel the gravitational influence of the MW itself. Tracers can also be affected by MW satellites; Garavito-Camargo et al. (2109) demonstrate that the Large Magellanic Cloud (LMC) induces a density wake in the MW DM, resulting in large-scale kinematic patterns in the MW stellar halo. In this work, we use spherical harmonic expansion (SHE) of the velocity fields of simulated stellar halos in an effort to disentangle perturbations on large scales (e.g., due to the LMC itself, as well as the LMC-induced DM wake) and small scales (due to substructure). Using the Garavito-Camargo et al. simulations, we demonstrate how the different terms in the SHE of the stellar velocity field reflect the different wake components and show that these signatures are a strong function of the LMC mass. An exploration of model halos built from accreted dwarfs suggests that stellar debris from massive, recent accretion events can produce much more power in the velocity angular power spectra than the perturbation from the LMC-induced wake. We therefore consider two models for the Sagittarius (Sgr) stream—the most recent, massive accretion event in the MW apart from the LMC—and find that the angular power on large scales is generally dominated by the LMC-induced wake, even when Sgr is included. We conclude that SHE of the MW stellar halo velocity field may therefore be a useful tool in quantifying the response of the MW DM halo to the LMC’s infall.

Central kiloparsec of NGC 1326 observed with SINFONI

Gas inflow processes in the vicinity of galactic nuclei play a crucial role in galaxy evolution and supermassive black hole growth. Exploring the central kiloparsec of galaxies is essential to shed more light on this subject. We present near-infraredH- andK-band results of the nuclear region of the nearby galaxy NGC 1326, observed with the integral-field spectrograph SINFONI mounted on the Very Large Telescope. The field of view covers 9″ × 9″ (650 × 650 pc2). Our work is concentrated on excitation conditions, morphology, and stellar content. The nucleus of NGC 1326 was classified as a LINER, however in our data we observed an absence of ionised gas emission in the centralr ∼ 3″. We studied the morphology by analysing the distribution of ionised and molecular gas, and thereby detected an elliptically shaped, circum-nuclear star-forming ring at a mean radius of 300 pc. We estimate the starburst regions in the ring to be young with dominating ages of < 10 Myr. The molecular gas distribution also reveals an elongated east to west central structure about 3″ in radius, where gas is excited by slow or mild shock mechanisms. We calculate the ionised gas mass of 8 × 105M⊙completely concentrated in the nuclear ring and the warm molecular gas mass of 187M⊙, from which half is concentrated in the ring and the other half in the elongated central structure. The stellar velocity fields show pure rotation in the plane of the galaxy. The gas velocity fields show similar rotation in the ring, but in the central elongated H2structure they show much higher amplitudes and indications of further deviation from the stellar rotation in the central 1″ aperture. We suggest that the central 6″ elongated H2structure might be a fast-rotating central disc. The CO(3–2) emission observations with the Atacama Large Millimeter/submillimeter Array reveal a central 1″ torus. In the central 1″ of the H2velocity field and residual maps, we find indications for a further decoupled structure closer to a nuclear disc, which could be identified with the torus surrounding the supermassive black hole.

Kinematics of main-sequence stars from the Gaia DR2 and PMA proper motions

ABSTRACTWe aim at analysis of kinematics of main-sequence stars from the GaiaDR2 and PMA catalogues as well as comparison of kinematic parameters derived from their proper motions. We decompose the stellar velocity field on to a set of vector spherical harmonics (VSH), and, using the relations between the decomposition coefficients and the Ogorodnikov–Milne (O–M) model parameters, calculate the latter. The method of VSH allowed to detect all systematic constituents present in the GaiaDR2 and PMA stellar velocity fields. We notice incompleteness of the O–M model, discuss the kinematic parameters derived within its framework, as well as significant decomposition coefficients that do not have analogues within this model. For separate analysis of the kinematic parameters in the Northern and Southern Galactic hemispheres, we apply the decomposition on to a set of zonal VSH (ZVSH). Modelling the stellar velocity field allowed to confirm the causes of some significant beyond-the-model harmonics. Based on stellar proper motions from the Gaia DR2 and PMA catalogues, we confirm the previous conclusion that the values of ω1 and $M^+_{23}$ O–M model parameters derived in the Northern and Southern Galactic hemispheres have opposite signs. This fact takes place due to a vertical gradient of the linear rotation velocity about the Galactic centre. We estimate influence of the vertical gradient on the value of solar velocity component Y⊙. We confirm that the beyond-the-model coefficients t211 and s310 are caused by the vertical gradient as well.

Ionized gas kinematics of massive elliptical galaxies in CALIFA and in cosmological zoom-in simulations

Context.Powerful active galactic nuclei (AGN) are supposed to play a key regulatory role on the evolution of their host galaxies by shaping the thermodynamic properties of their gas component. However, little is known as to the nature and the visibility timescale of the kinematical imprints of AGN-driven feedback. Gaining theoretical and observational insights into this subject is indispensable for a thorough understanding of the AGN-galaxy coevolution and could yield empirical diagnostics for the identification of galaxies that have experienced a major AGN episode in the past.Aims.We present an investigation of kinematical imprints of AGN feedback on the warm ionized gas medium (WIM) of massive early-type galaxies (ETGs). To this end, we take a two-fold approach that involves a comparative analysis of Hαvelocity fields in 123 local ETGs from the CALIFA (Calar Alto Legacy Integral Field Area Survey) integral field spectroscopy survey with 20 simulated galaxies from high-resolution hydrodynamic cosmological SPHgal simulations. The latter were resimulated for two modeling setups, one with and another without AGN feedback.Methods.In order to quantify the effects of AGN feedback on gas kinematics, we measured three parameters that probe deviations from simple regular rotation by using the kinemetry package. These indicators trace the possible presence of distinct kinematic components in Fourier space (k3, 5/k1), variations in the radial profile of the kinematic major axis (σPA), and offsets between the stellar and gas velocity fields (Δϕ). These quantities were monitored in the simulations from a redshift 3 to 0.2 to assess the connection between black hole accretion history, stellar mass growth, and the kinematical perturbation of the WIM.Results.Observed local massive galaxies show a broad range of irregularities, indicating disturbed warm gas motions, which is irrespective of being classified via diagnostic lines as AGN or not. Simulations of massive galaxies with AGN feedback generally exhibit higher irregularity parameters than without AGN feedback, which is more consistent with observations. Besides AGN feedback, other processes like major merger events or infalling gas clouds can lead to elevated irregularity parameters, but they are typically of shorter duration. More specifically,k3, 5/k1is most sensitive to AGN feedback, whereas Δϕis most strongly affected by gas infall.Conclusions.We conclude that even if the general disturbance of the WIM velocity is not a unique indicator for AGN feedback, irregularity parameters that are high enough to be consistent with observations can only be reproduced in simulations with AGN feedback. Specifically, an elevated value for the deviation from simple ordered motion is a strong sign for previous events of AGN activity and feedback.

Young stars as tracers of a barred-spiral Milky Way

Abstract Identifying the structure of our Galaxy has always been fraught with difficulties, and while modern surveys continue to make progress building a map of the Milky Way, there is still much to understand. The arm and bar features are important drivers in shaping the interstellar medium, but their exact nature and influence still require attention. We present results of smoothed particle hydrodynamic simulations of gas in the Milky Way including star formation, stellar feedback, and ISM cooling, when exposed to different arm and bar features, with the aim of better understanding how well newly formed stars trace out the underlying structure of the Galaxy. The bar is given a faster pattern speed than the arms, resulting in a complex, time-dependent morphology and star formation. Inter-arm branches and spurs are easily influenced by the bar, especially in the two-armed spiral models where there is a wide region of resonance overlap in the disc. As the bar over-takes the spiral arms it induces small boosts in star formation and enhances spiral features, which occur at regularly spaced beat-like intervals. The locations of star formation events are similar to those seen in observational data, and do not show a perfect 1:1 correspondence with the underlying spiral potential, though arm tangencies are generally well traced by young stars. Stellar velocity fields from the newly formed stars are compared to data from Gaia DR2, showing that the spiral and bar features can reproduce many of the non-axisymmetric features seen in the data. A simple analytical model is used to show many of these feature are a natural response of gas to rigidly rotating spiral and bar potentials.

Kinematic Parameters of the Stellar Velocity Field within 3 kpc of the Sun Based on the Gaia Data Release 2 with Radial Velocities Catalogue

The paper is devoted to determining the parameters of the three-dimensional Ogorodnikov—Milne kinematic model based on the Gaia DR2 star catalogue (the subset of seven million stars containing radial velocities). The behavior of the parameters as a function of the distance to stars is studied. The parameters derived from the stellar proper motions and radial velocities agree well with one another. It is noted that the angular velocity of rotation retains its stability up to distances of ~3 kpc, while the parameter responsible for the translational motion along the Y axis abruptly begins to change from distances starting from 1 kpc.

Constraining the Milky Way non-axisymmetries with Gaia

AbstractThe unprecedented amount and accuracy of kinematic data from the second release of the Gaia mission have started revolutionizing our understanding of the dynamics of the Milky Way disk. The detailed stellar velocity field in the Galactic disk should allow us to constrain with unprecedented precision the parameters of the non-axisymmetric modes of the disk. We present here the status of our current modelling efforts in this area, and their implication on the dynamics of the Galactic bar in particular.

The ultra-diffuse galaxy NGC 1052-DF2 with MUSE

The so-called ultra-diffuse galaxy NGC 1052-DF2 was announced to be a galaxy lacking dark matter based on a spectroscopic study of its constituent globular clusters. Here we present the first spectroscopic analysis of the stellar body of this galaxy using the MUSE integral-field spectrograph at the (ESO) Very Large Telescope. The MUSE datacube simultaneously provides DF2’s stellar velocity field and systemic velocities for seven globular clusters (GCs). We further discovered three planetary nebulae (PNe) that are likely part of this galaxy. While five of the clusters had velocities measured in the literature, we were able to confirm the membership of two more candidates through precise radial velocity measurements, which increases the measured specific frequency of GCs in DF2. The mean velocity of the diffuse stellar body, 1792.9+1.4−1.8 km s−1, is consistent with the mean globular cluster velocity. We detect a weak but significant velocity gradient within the stellar body, with a kinematic axis close to the photometric major axis, making it a prolate-like rotator. We estimate a velocity dispersion from the clusters and PNe of σint = 10.6−2.3+3.9 km s−1. The velocity dispersion σDF2⋆(Re) for the stellar body within one effective radius is 10.8+3.2−4.0 km s−1. Considering various sources of systemic uncertainties, this central value varies between 5 and 13 km s−1, and we conservatively report a 95% confidence upper limit to the dispersion within one Re of 21 km s−1. We provide updated mass estimates based on these dispersions corresponding to the different distances to NGC 1052-DF2 that have been reported in the recent literature.

The first 62 AGN observed with SDSS-IV MaNGA – III: stellar and gas kinematics

We investigate the effects of Active Galactic Nuclei (AGN) on the gas kinematics of their host galaxies, using MaNGA data for a sample of 62 AGN hosts and 109 control galaxies (inactive galaxies). We compare orientation of the line of nodes (kinematic Position Angle - PA) measured from the gas and stellar velocity fields for the two samples. We found that AGN hosts and control galaxies display similar kinematic PA offsets between gas and stars. However, we note that AGN have larger fractional velocity dispersion $\sigma$ differences between gas and stars [$\sigma_{frac}=(\sigma_{\rm gas}-\sigma_{stars})/\sigma_{\rm stars}$] when compared to their controls, as obtained from the velocity dispersion values of the central (nuclear) pixel (2.5" diameter). The AGN have a median value of $\sigma_{\rm frac}$ of $<\sigma_{frac}>_{\rm AGN}=0.04$, while the the median value for the control galaxies is $<\sigma_{frac}>_{\rm CTR}=-0.23$. 75% of the AGN show $\sigma_{frac}>-0.13$, while 75% of the normal galaxies show $\sigma_{\rm frac}<-0.04$, thus we suggest that the parameter $\sigma_{\rm frac}$ can be used as an indicative of AGN activity. We find a correlation between the [OIII]$\lambda$5007 luminosity and $\sigma_{frac}$ for our sample. Our main conclusion is that the AGN already observed with MaNGA are not powerful enough to produce important outflows at galactic scales, but at 1-2 kpc scales, AGN feedback signatures are always present on their host galaxies.

Hot grain dynamics by electric charging and magnetic trapping in debris disks

The recent discovery of hot dust grains in the vicinity of main-sequence stars has become a hot issue among the scientific community of debris disks. Hot grains must have been enormously accumulated near their sublimation zones, but it is a mystery how such a high concentration of hot grains is sustained. The most difficult conundrum is that the size of hot dust grains is estimated to lie in the submicrometer range, while submicrometer-sized grains are instantly swept away from near-stellar environments by stellar radiation pressure. One and only mechanism proposed for prolonging the residence time of hot grains in the near-stellar environments is trapping of charged nanoparticles by stellar magnetic fields. We revisit the model of magnetic grain trapping around main-sequence stars of various spectral classes by taking into account sublimation and electric charging of the grains. The model of magnetic grain trapping predicts that hot dust grains are present in the vicinity of main-sequence stars with high rotation velocities and intermediate magnetic-field strengths. On the contrary, we find that the detection of hot dust grains has no correlation with the rotation velocities of central stars nor the magnetic field strengths of the stars. Our numerical evaluation of electric grain charging indicates that the surface potential of submicrometer-sized grains in the vicinity of main-sequence stars is typically 4– 5V, which is one order of magnitude smaller than the value assumed by the model of magnetic grain trapping. On the basis of our numerical simulation on sublimation of dust grains in the vicinity of a star, it turns out that their lives end due to sublimation in a timescale much shorter than the period of one revolution at the gyroradius. It is, therefore, infeasible to dynamically extend the dwell time of hot grains inside the sublimation zone by magnetic trapping, while we cannot completely rule out the possibility of magnetic grain trapping outside the sublimation zone where the strength of stellar magnetic field has been underestimated in the previous model. Nevertheless, the independence of hot dust detection on the stellar rotational velocity and magnetic field strength favors a scenario that some other (yet unnoticed/overlooked) ubiquitous mechanism of grain trapping is at work.

SDSS-IV MaNGA: characterizing non-axisymmetric motions in galaxy velocity fields using the Radon transform

We show how the Radon transform (defined as a series of line integrals through an image at different orientations and offsets from the origin) can be used as a simple, non-parametric tool to characterize galaxy velocity fields, specifically their global kinematic position angles (PA_k) and any radial variation or asymmetry in PA_k. This method is fast and easily automated, making it particularly beneficial in an era where IFU and interferometric surveys are yielding samples of thousands of galaxies. We demonstrate the Radon transform by applying it to gas and stellar velocity fields from the first ~2800 galaxies of the SDSS-IV MaNGA IFU survey. We separately classify gas and stellar velocity fields into five categories based on the shape of their radial PA_k profiles. At least half of stellar velocity fields and two-thirds of gas velocity fields are found to show detectable deviations from uniform coplanar circular motion, although most of these variations are symmetric about the center of the galaxy. The behavior of gas and stellar velocity fields is largely independent, even when PA_k profiles for both components are measured over the same radii. We present evidence that one class of symmetric PA_k variations is likely associated with bars and/or oval distortions, while another class is more consistent with warped disks. This analysis sets the stage for more in-depth future studies which explore the origin of diverse kinematic behavior in the galaxy population.

SDSS-IV MaNGA: stellar angular momentum of about 2300 galaxies: unveiling the bimodality of massive galaxy properties

We measure $\lambda_{R_e}$, a proxy for galaxy specific stellar angular momentum within one effective radius, and the ellipticity, $\epsilon$, for about 2300 galaxies of all morphological types observed with integral field spectroscopy as part of the MaNGA survey, the largest such sample to date. We use the $(\lambda_{R_e}, \epsilon)$ diagram to separate early-type galaxies into fast and slow rotators. We also visually classify each galaxy according to its optical morphology and two-dimensional stellar velocity field. Comparing these classifications to quantitative $\lambda_{R_e}$ measurements reveals tight relationships between angular momentum and galaxy structure. In order to account for atmospheric seeing, we use realistic models of galaxy kinematics to derive a general approximate analytic correction for $\lambda_{R_e}$. Thanks to the size of the sample and the large number of massive galaxies, we unambiguously detect a clear bimodality in the $(\lambda_{R_e}, \epsilon)$ diagram which may result from fundamental differences in galaxy assembly history. There is a sharp secondary density peak inside the region of the diagram with low $\lambda_{R_e}$ and $\epsilon < 0.4$, previously suggested as the definition for slow rotators. Most of these galaxies are visually classified as non-regular rotators and have high velocity dispersion. The intrinsic bimodality must be stronger, as it tends to be smoothed by noise and inclination. The large sample of slow rotators allows us for the first time to unveil a secondary peak at +/-90 degrees in their distribution of the misalignments between the photometric and kinematic position angles. We confirm that genuine slow rotators start appearing above a stellar mass of 2\times10^{11} M_{\odot}$ where a significant number of high-mass fast rotators also exist.