Velocity Dispersion Research Articles (Page 1)

Abstract We observed the X-ray-bright ultraluminous infrared galaxy IRAS 05189−2524 with XRISM during its performance verification phase. The unprecedented energy resolution of the onboard X-ray microcalorimeter revealed complex spectral features at ∼7–9 keV, which can be interpreted as blueshifted Fe XXV / XXVI absorption lines with various velocity dispersions, originating from ultrafast outflow (UFO) components with multiple bulk velocities of ∼0.076 c , ∼0.101 c , and ∼0.143 c . In addition, a broad Fe–K emission line was detected around ∼7 keV, forming a P Cygni profile together with the absorption lines. The onboard X-ray CCD camera revealed a 0.4–12 keV broadband spectrum characterized by a neutrally absorbed power-law continuum with a photon index of ∼2.3 and intrinsic flare-like variability on timescales of ∼10 ks, both of which are likely associated with near-Eddington accretion. We also found potential variability of the UFO parameters on a timescale of ∼140 ks. Using these properties, we propose new constraints on the outflow structure and suggest the presence of multiple outflowing regions on scales of about tens to 100 Schwarzschild radii, located within roughly 2000 Schwarzschild radii. Since both the estimated momentum and energy outflow rates of the UFOs exceed those of galactic molecular outflows, our results indicate that powerful, multivelocity UFOs are already well developed during a short-lived evolutionary phase following a major galaxy merger, characterized by intense starburst activity and likely preceding the quasar phase. This system is expected to evolve into a quasar, sustaining strong UFO activity and suppressing star formation in the host galaxy.

The fundamental plane (FP) is an empirical scaling relation linking the structure and dynamics of early-type galaxies. However, the traditionally used luminosity-based FP is sensitive to variations in stellar populations and dust, limiting its reliability at high redshifts. We investigate the redshift evolution of the stellar mass fundamental plane (SM-FP) as a more physically motivated alternative, using a sample of spheroidal galaxies selected from the Horizon Run 5 (HR5) cosmological hydrodynamical simulation. We selected spheroidal galaxies mainly based on morphological criteria, using structural parameters such as the asymmetry parameter (A) and the Sérsic index (n_ Sérsic ), and constructed the SM-FP by replacing surface brightness with stellar mass surface density. We then studied the evolution of the FP parameters and its scatter over the redshift range from ( z = 0.625 ) to ( z = 6 ). Our analysis reveals a well-defined SM-FP existing as early as ( z ∼ 6 ), exhibiting a low intrinsic scatter (∼0.07 dex). The FP slope parameters evolve systematically, with the velocity dispersion coefficient decreasing and the surface density coefficient also decreasing in magnitude towards higher redshifts. The FP tightness improves when selecting slow rotators with ( V_ ̊m rot /σ_e <0.55). Additionally, we observe systematic dependencies of FP residuals on the stellar age, specific star formation rate (sSFR), and V_ ̊m rot /σ_e, highlighting the importance of internal kinematics over age or sSFR in defining the FP. Our results demonstrate that the structural and dynamical scaling relations of spheroidal galaxies were established early in cosmic history, with the SM-FP established robustly by z ≈ 6. The systematic evolution of FP parameters with redshift can provide crucial insights into the processes governing galaxy assembly and morphological evolution.

We present a new high-precision parametric strong lensing total mass reconstruction of the Euclid Early Release Observations (ERO) galaxy cluster Abell 2390 at redshift z = 0.231. We include in this analysis 35 multiple images from 13 background sources, of which 25 are spectroscopically confirmed thanks to observations from the Multi Unit Spectroscopic Explorer (MUSE), spanning a redshift range from z = 0.535 to z = 4.877. After fully re-analysing the MUSE spectroscopy, we combined it with archival spectroscopic catalogues, thus allowing us to select 65 secure cluster members. We further complemented this sample with 114 photometric member galaxies, identified within the Euclid VIS and NISP imaging down to magnitude ̋E = 23. We also measured the stellar velocity dispersions for 22 cluster members in order to calibrate the Faber--Jackson relation and hence the scaling relations for the sub-halo mass components. We tested and compared 11 total mass parametrisations of the galaxy cluster with increasing complexity. To do so, we employed the new parametric strong lensing modelling code Gravity.jl . Our best-fit total mass parametrisation is characterised by a single large-scale halo, 179 sub-halo components, and an external shear term. The reference model yields a mean scatter between the model-predicted and observed positions of the multiple images of . We were able to quantify the systematics arising from our modelling choices by taking advantage of all the different explored total mass parametrisations. When comparing our results with those from other lensing studies, we noticed an overall agreement in the reconstructed cluster total mass profile in the outermost strong lensing regime. The discrepancy in the innermost region of the cluster (a few kiloparsecs from the brightest cluster galaxy, where few or no strong lensing features are observed) could possibly be ascribed to the different data and modelling choices.

Abstract Understanding how the dynamical state of the interstellar medium (ISM) changes across spatial scales can provide important insights into how the gas is organized and ultimately collapses to form stars. To this end, we present ALMA 12 CO(2–1) observations at 7 pc (0 . ″ 4) spatial resolution across a 1.4 kpc × 5.6 kpc ( 1 . ′ 3 × 1 . ′ 3 ) region located in the disk of the nearby ( D = 3.5 Mpc), massive, star-forming galaxy NGC 253. We decompose this emission with a hierarchical, multiscale dendrogram algorithm to identify 2463 structures with deconvolved sizes ranging from ∼3 to 300 pc, complete to a limiting mass of 10 4 M ⊙ . By comparing the virial parameter of these structures against physical properties including size, mass, surface density, velocity dispersion, and hierarchical position, we carry out a comprehensive search for a preferred scale at which gravitationally bound structures emerge. Ultimately, we do not identify evidence of an emergent scale for bound objects in our data, nor do we find a significant correlation between the virial parameter and structure sizes. These findings suggest that simple observational estimates of gravitational binding cannot be used to define molecular clouds and emphasize the need for multiscale approaches to characterize the ISM.

Abstract Active galactic nuclei (AGN) are important drivers of galactic evolution; however, the underlying physical processes governing their properties remain uncertain. In particular, the specific cause for the generation of the broad-line region is unclear. There is a region where the underlying accretion disc atmosphere becomes cool enough for dust condensation. Using models of the disc’s vertical structure, accounting for dust condensation and irradiation from the central source, we show that their upper atmospheres become extended, dusty, and radiation-pressure-supported. Due to the density–temperature dependence of dust condensation, this extended atmosphere forms as the dust abundance slowly increases with height, resulting in density and temperature scale heights considerably larger than the gas pressure scale height. We show that such an atmospheric structure is linearly unstable. An increase in the gas density raises the dust sublimation temperature, leading to an increased dust abundance, a higher opacity, and hence a net vertical acceleration. Using localised 2D hydrodynamic simulations, we demonstrate the existence of our linear instability. In the non-linear state, the disc atmosphere evolves into “fountains” of dusty material that are vertically launched by radiation pressure before being exposed to radiation from the central source, which sublimates the dust and shuts off the radiative acceleration. These dust-free clumps then evolve ballistically, continuing upward before falling back towards the disc under gravity. This clumpy ionized region has velocity dispersions ≳ 1000 km s−1. This instability and our simulations are representative of the Failed Radiatively Accelerated Dusty Outflow (FRADO) model proposed for the AGN broad-line region.

Abstract We used CO (2-1) and CO (1-0) data cubes to identify molecular clouds and study their kinematics and dynamics in three nearby galaxies and the inner Milky Way. When observed at similar spatial and velocity resolutions, molecular clouds in the same mass range across these galaxies show broadly comparable physical properties and similar star formation rates (SFRs). However, this comparability depends on smoothing Milky Way clouds to match the resolution of the extragalactic observations. The beam effect can artificially inflate cloud sizes, leading to inaccurate estimates of radius, density, and virial parameters. By comparing high-resolution and smoothed Milky Way data, we established criteria to exclude beam-affected clouds in the extragalactic sample. After applying this filter, cloud properties remain consistent across galaxies, though some clouds in NGC 5236 show elevated velocity dispersions, likely due to environmental effects. In the inner Milky Way, molecular clouds fall into two groups: those with clumps and those without. Clump-associated clouds are more massive, denser, have higher velocity dispersions, lower virial parameters, and stronger 8μm emission, suggesting more intense feedback. Strong correlations are found between cloud mass and total clump mass, clump number, and the mass of the most massive clump. These results suggest that a cloud’s physical conditions regulate its internal clump properties and, in turn, its star-forming potential.

Abstract In the solution of the Jeans equations for axisymmetric galaxy models the “b-ansatz” is often adopted to prescribe the relation between the vertical and radial components of the velocity dispersion tensor, and close the equations. However, b affects the resulting azimuthal velocity fields quite indirectly, so that the analysis of the model kinematics is usually performed after numerically solving the Jeans equations, a time consuming approach. In a previous work we presented a general method to determine the main properties of the kinematical fields resulting in the b-ansatz framework before solving the Jeans equations; results were illustrated by means of disk galaxy models. In this paper we focus more specifically on realistic ellipsoidal galaxy models. It is found that how and where b affects the galaxy kinematical fields is mainly dependent on the flattening of the stellar density distribution, moderately on the presence of a Dark Matter halo, and much less on the specific galaxy density profile. The main trends revealed by the numerical exploration, in particular the fact that more flattened systems can support larger b-anisotropy, are explained with the aid of simple ellipsoidal galaxy models, for which most of the analysis can be conducted analytically. The obtained results can be adopted as guidelines for model building and in the interpretation of observational data.

Abstract Gaia observations have revealed over a million stellar binary candidates within ∼1 kpc of the Sun, predominantly characterized by orbital separations >10 3 au and eccentricities >0.7. The prevalence of such wide, eccentric binaries has proven challenging to explain through canonical binary formation channels. However, recent advances in our understanding of three-body binary formation (3BBF)—new binary assembly by the gravitational scattering of three unbound bodies (3UB)—have shown that 3BBF in star clusters can efficiently generate wide, highly eccentric binaries. We further explore this possibility by constructing a semi-analytic model of the Galactic binary population in the solar neighborhood, originating from 3BBF in star clusters and subsequently migrating to the solar neighborhood within a Hubble time. The model relies on 3BBF scattering experiments to determine how the 3BBF rate and resulting binary properties scale with local stellar density, velocity dispersion, and physically motivated limits to 3UB encounters within a clusters’ tidal field. The Galactic star cluster population is modeled by incorporating up-to-date prescriptions for the Galaxy’s star formation history as well as the birth properties and internal evolution of its star clusters. Finally, we account for binary disruption induced by perturbations from stellar interactions before cluster dissolution and the subsequent changes and disruption of binary orbital elements induced by dynamical interactions in the Galactic field. Without any explicit fine-tuning, our model closely reproduces the total number of Gaia’s wide binaries and the separation and eccentricity distributions, suggesting that 3BBF may be an important formation channel for these enigmatic systems.

Ultrasound Shear Wave Attenuation Estimates are Sensitive to In situ Fluid Content: In vitro and Ex vivo Studies.

DisperPy: A machine learning based tool to automatically pick group velocity dispersion curves from earthquakes

Abstract The possibility of forming a two-color bright–dark light bullet in a crystal containing quasi-resonant impurity centers was studied. A bright–dark light bullet is a two-color laser beam along which a dark spot of intensity dip is propagating. It is shown that such a light bullet is formed if the group velocity dispersion for the fundamental frequency is positive. It is important that the mismatch between the phase velocities for the fundamental frequency and for the second harmonic frequency prevail over the corresponding mismatch between the group velocities. The refractive index for the fundamental frequency must be greater than the refractive index for the second harmonic frequency. The upper restrictions for the temporal duration of the dark spot and for the transverse size of the laser beam are obtained. These restrictions are determined by the value of the phase-group mismatch, which, in turn, depends on the parameters of quasi-resonant impurities.

Abstract Recent observations from JWST have revealed an abundant population of active galactic nuclei (AGN) and so-called “Little Red Dots” (LRDs) at 2 ≲ z ≲ 11, many of which are characterized by V-shaped UV-to-optical continua with turnovers around the Balmer limit. The physical nature of these LRDs is unclear, and it remains debated whether the peculiar spectral shape originates from AGN, compact galaxies, or both. We present the analysis of new NIRSpec-IFU data from the BlackTHUNDER JWST Large Programme and archival NIRSpec-MSA data of a lensed LRD at z = 7.04. The spectra confirm the presence of a smooth Balmer break and a broad Hβ tracing the Broad Line Region (BLR) of an AGN. The small velocity dispersion of the Hβ narrow component indicates a small dynamical mass of the host galaxy of Mdyn < 4 × 108 M⊙, which implies that the stellar population cannot contribute more than 10% to the optical continuum. We show that the Balmer break can be well described by an AGN continuum absorbed by very dense (nH ∼ 1010 cm−3) and nearly dust-free gas along our line-of-sight (possibly gas in the BLR or its surrounding). The same gas is expected to produce Hβ absorption, at a level consistent with a tentative detection (3σ) in the high-resolution spectrum. Such a non-stellar origin of the Balmer break may apply to other LRDs, and would alleviate the issue of extremely high stellar mass surface densities inferred in the case of a stellar interpretation of the Balmer break. We note that this is a rare case of a black hole that is overmassive relative to both the host galaxy stellar and dynamical masses. We finally report indications of variability and the first attempt of AGN reverberation mapping at such an early epoch.

Recent studies using Gaia data have reported tidal tail detections for tens to hundreds of open clusters. However, a comprehensive assessment of the reliability and completeness of these detections is lacking. This work aims to summarise the expected properties of tidal tails based on N-body simulations, review the reliability of tidal tail detections in the literature, and grade them according to a set of diagnostic tests. We also provide an overview of the general characteristics of tidal tails available in the literature. We used a grid of 68--20000 simulated clusters and analysed the formation and evolution of the tidal tails. We compiled 122 catalogues from the recent literature, encompassing 58 unique clusters within 500 pc of the Sun. We employed various tests based on photometric, morphological, and dynamical signatures and comparisons with simulated clusters to grade the tidal tails as gold, silver, and bronze. One of the primary tests was to measure apparent torsion in the Galactocentric XY plane. Based on the simulations, we analysed the complex morphology of the tidal tails and their properties (such as their size, span, stellar types, number density, and mass function) at various cluster masses and ages. During the first 100--200 Myr of evolution, the tails typically form a characteristic S shape, with an amplitude that scales with cluster mass. The tail span increases at a rate of ≈4 times the initial velocity dispersion, and the near-tail (within 100 pc of the cluster) is predominantly populated by recent escapees. In evaluating 122 published tidal tail catalogues, we found that 15 gold-quality catalogues and 55 silver-quality catalogues passed the majority of the tests. The remaining 51 catalogues were graded as bronze; care should be taken before using these catalogues for further analysis. The age, metallicity, binary fraction, and mass function of stars in the tails were generally consistent with those of their parent clusters. The simulations presented here provide first-order approximations of the structure and evolution of the tidal tails. The gold and silver-grade catalogues (69 catalogues of 40 clusters) represent reliable samples for detailed analyses of tidal tails. Future spectroscopic and astrometric data from large-scale surveys will be essential for further validation and for leveraging tidal tails as tracers of cluster dissolution and the Galactic potential.

Abstract We re-analysed ALMA observations of the [O iii] λ88μm emission line in JADES-GS-z14-0, so one of the most distant spectroscopically confirmed galaxy at z=14.18. Our analysis shows a tentative detection of a velocity gradient of [O iii] λ88μm using three independent tests: (1) construction of moment maps; (2) extraction of integrated spectra from a grid of apertures; and (3) spectro-astrometry in both the image and uv planes, confirming the presence of the velocity gradient at 3σ significance. We performed kinematical fitting using the KinMS code and estimated a dynamical mass of log10(Mdyn/$\rm M_\odot$)= 9.4$^{+0.8}_{-0.4}$, with the bulk of the uncertainties due to the degeneracy between dynamical mass and inclination. We measure an upper limit on the velocity dispersion (σv) of <40 km s−1 which results in an estimate of Vrot/σ > 2.5. This result, if confirmed with higher-resolution observations, would imply that kinematically cold discs are already in place at z ∼ 14. Comparison with mock observations from the SERRA cosmological simulations confirms that even low-resolution observations are capable of detecting a velocity gradient in z > 10 galaxies as compact as JADES-GS-z14-0. This work shows that deeper ALMA or JWST/NIRSpec IFS observations with high spatial resolution will be able to estimate an accurate dynamical mass for JADES-GS-z14-0, providing an upper limit to the stellar mass of this over-luminous galaxy.

Molecular clouds (MCs) are active sites of star formation in galaxies, and their formation and evolution are largely affected by stellar feedback. This includes outflows and winds from newly formed stars, radiation from young clusters, and supernova explosions. High-resolution molecular line observations allow for the identification of individual star-forming regions and the study of their integrated properties. Moreover, state-of-the-art simulations are now capable of accurately replicating the evolution of MCs, including all key stellar feedback processes. We present ^13CO(2-1) synthetic observations of the simulations produced using the radiative transfer code RADMC-3D, matching the observational setup of the survey. From these synthetic observations, we identified the population of MCs using hierarchical clustering and analysed them to provide insights into the interpretation of observed MCs as they evolve. The flux distributions of the post-processed synthetic observations and the properties of the MCs, namely, radius, mass, velocity dispersion, virial parameter, and surface density, are consistent with those of Both samples of MCs occupy the same regions in the scaling relation plots; however, the average distributions of MCs at different evolutionary stages do not overlap on the plots. This highlights the reliability of our approach in modelling and suggests that MCs at different evolutionary stages contribute to the scatter in observed scaling relations. We study the trends in MC properties, morphologies, and fragmentation over time to analyse their physical structure as they form, evolve, and are destroyed. MCs appear as small diffuse cloudlets in early stages, and this is followed by their evolution to filamentary structures before being shaped by stellar feedback into 3D bubbles and getting dispersed. These trends in the observable properties of MCs are consistent with other realisations of simulations and provide strong evidence that clouds exhibit distinct morphologies over the course of their evolution.

Surface wave imaging based on ambient noise, especially with the deployment of increasingly dense arrays (such as nodal seismometers and Distributed Acoustic Sensing), has become an effective tool for investigating subsurface velocity structures. While segmenting dense arrays into subarrays has emerged as a promising approach, traditional subarray surface wave imaging (SSWI) methods face challenges in positioning the average phase velocity dispersion data of subarrays, leading to velocity jumps and poor lateral constraints. We propose a novel subarray surface wave direct imaging (SSWDI) method that establishes a sensitivity kernel between subarray average dispersion data and subsurface parameters. Through numerical experiments and real-world applications, we demonstrate that SSWDI can reduce velocity artifacts compared to traditional methods. The method’s key advantages include inherent spatial smoothing constraints and the ability to jointly utilize multiscale subarray dispersion data, providing more reliable constraints on subsurface S-wave velocity structures from shallow to deep depths. The SSWDI method shows broad application potential in the future.

We document an application of ambient noise tomography (ANT) for mineral exploration near the town of Marathon, Ontario, Canada. Our study area consists of host rocks for platinum group metals and copper. ANT is performed to generate a three-dimensional (3D) shear-wave velocity (Vs) model for the exploration of Marathon deposits. The ambient noise recordings used in this study were collected using 90 vertical geophones for 26 days. We use the recordings to compute the noise correlation functions and estimate Rayleigh wave phase and group velocity dispersion curves. Then these dispersion measurements are used for 2D tomography to create 2D velocity maps that are inverted to obtain a 3D Vs model. Our independently produced Vs model agrees well with measured Vs from downhole Vs logging. Furthermore, the developed 3D velocity model aids in interpretation of our study area that can be helpful for future mineral exploration and for improving understanding of the mineral generation model.

Comparing XRISM Cluster Velocity Dispersions with Predictions from Cosmological Simulations: Are Feedback Models Too Ejective?

Abstract The multifunctional properties of 2D AlB 3 nanosheets are systematically investigated by using crystal structure prediction, first‐principles calculations, and molecular dynamics simulations. The identified ground‐state structure, designated as AlB 3 ‐1, features a unique layered architecture consisting of two vertically stacked sandwich units that share a central borophene layer. This arrangement leads to increased mechanical strength (with an in‐plane modulus surpassing that of graphene) and excellent thermal stability (retaining integrity in ab initio molecular dynamics at 1600K). Analysis of the electronic structure revealed the presence of multiple Dirac cones near the Fermi level accompanied by linear energy dispersion and high Fermi velocities (≈10 6 m s −1 ), indicating massless charge carriers. Moderate electron–phonon coupling predicts a superconducting transition temperature of 28.84K. The structure also exhibits balanced lattice thermal conductivity (≈16.50 W m −1 K −1 ). Chemical bonding analysis indicated strong covalent B–B interactions and partially ionic Al─B bonds that contribute to the overall structural integrity. Furthermore, low‐lying allotropes (AlB 3 ‐2–10) display diverse bonding motifs and rich electronic behaviors, including metallic phases with Dirac‐like dispersions. In addition to broadening the understanding of boride‐based 2D materials, these findings highlight the potential of AlB 3 nanosheets as promising candidates for use in nanoelectronics, superconductive and thermoelectric materials, and nanoscale mechanics.

Abstract The streaming instability (SI), driven by aerodynamic coupling between solids and gas under a global radial pressure gradient, concentrates solids and facilitates planetesimal formation. Unstratified simulations are commonly used to study the SI, based on the assumption that they approximate conditions near the disk midplane. However, it remains unclear how accurately these unstratified simulations capture the midplane dust–gas dynamics in stratified disks. To address this, we examine the saturated state of the SI in stratified simulations and compare the dust–gas dynamics to those in unstratified simulations across various radial pressure gradients. To this end, we consider a dimensionless dust stopping time ( τ s ) of 0.1 and perform 2D axisymmetric, stratified simulations. We find that the formation of dust filaments during dust settling exhibits morphological similarities to those in unstratified simulations. Vertical gravity acts to redistribute momentum vertically in response to momentum flux, resulting in midplane velocities in the center-of-mass frame that are consistent with those from unstratified models at any given pressure gradient. Furthermore, the velocity dispersions and density distributions of the gas and dust near the midplane of our stratified simulations closely match those in unstratified simulations. While further exploration across the parameter space is needed, our results suggest that, for τ s = 0.1, unstratified simulations represent well the midplane dust–gas dynamics in stratified disks before any strong clumping occurs. Consequently, our results confirm that in the saturated state, the streaming turbulence in stratified simulations behaves similarly to that in unstratified simulations for the parameter values explored here.