Gas Disk Research Articles

Self-consistent N-body simulation of planetesimal-driven migration. I. The trajectories of single planets in the uniform background

Abstract Recent exoplanet observations have revealed a diversity of exoplanetary systems, which suggests the ubiquity of radial planetary migration. One powerful known mechanism of planetary migration is planetesimal-driven migration (PDM), which can let planets undergo significant migration through gravitational scattering with planetesimals. In this series of papers, we present the results of our high-resolution, self-consistent N-body simulations of PDM, in which gravitational interactions among planetesimals, the gas drag, and Type I migration are all taken into account. In this first paper (Paper I), we investigate the migration of a single planet through PDM within the framework of the classical standard disk model (the minimum-mass solar nebula model). Paper I aims to improve our understanding of planetary migration through PDM, addressing previously unexplored aspects of both the gravitational interactions among planetesimals and the interactions with disk gas. Our results show that even small protoplanets can actively migrate through PDM. Such active migration can act as a rapid radial diffusion mechanism for protoplanets and significantly influence the early stages of planetary formation (i.e., during the runaway growth phase). Moreover, a fair fraction of planets migrate outward. This outward migration may offer a potential solution for the “planet migration problem” caused by Type I migration and gives a natural mechanism for outward migration assumed in many recent scenarios for the formation of outer planets.

Modeling ALMA Observations of the Warped Molecular Gas Disk in the Red Nugget Relic Galaxy NGC 384

We present 0.″22 resolution CO(2–1) observations of the circumnuclear gas disk in the local compact galaxy NGC 384 with the Atacama Large Millimeter/submillimeter Array (ALMA). While the majority of the disk displays regular rotation with projected velocities rising to 370 km s−1, the inner ∼0.″5 exhibits a kinematic twist. We develop warped disk gas-dynamical models to account for this twist, fit those models to the ALMA data cube, and find a stellar mass-to-light ratio in the H band of M/L H = 1.34 ± 0.01 [1σ statistical] ±0.02 [systematic] M ⊙/L ⊙ and a supermassive black hole (BH) mass (M BH) of M BH =(7.26−0.48+0.43[1σstatistical]−1.00+0.55[systematic])×108M⊙ . In contrast to most previous dynamical M BH measurements in local compact galaxies, which typically found over-massive BHs compared to the local BH mass−bulge luminosity and BH mass−bulge mass relations, NGC 384 lies within the scatter of those scaling relations. NGC 384 and other local compact galaxies are likely relics of z ∼ 2 red nuggets, and over-massive BHs in these relics indicate BH growth may conclude before the host galaxy stars have finished assembly. Our NGC 384 results may challenge this evolutionary picture, suggesting there may be increased scatter in the scaling relations than previously thought. However, this scatter could be inflated by systematic differences between stellar- and gas-dynamical measurement methods, motivating direct comparisons between the methods for NGC 384 and the other compact galaxies in the sample.

Origin of Ca II emission around polluted white dwarfs

Dozens of white dwarfs with anomalous metal polluted atmospheres are currently known to host dust and gas discs. The line profiles of the Ca II triplet emitted by the gas discs show a significant asymmetry. In recent decades, researchers have also discovered several minor planets orbiting such white dwarf stars. The most challenging burden of modelling gas discs around metal polluted white dwarfs is to simultaneously explain the asymmetry and metal pollution of the star's atmosphere over a certain period of time. Furthermore, models should also be consistent with other aspects of the observations, such as the morphology of the emission lines. This paper aims to construct a self-consistent model to explain the simultaneous white dwarf pollution and Ca II line asymmetry over at least three years. In our model, an asteroid disintegrates in an eccentric orbit, periodically entering below the star's Roche limit. The debris resulting from the disintegration sublimates at a temperature of 1500 K, producing gas that viscously spreads to form a disc. The evolution of the disc is studied over a period of 1.2 years (over 21000 orbits) using two-dimensional hydrodynamic simulations. Synthetic Ca II line profiles are calculated using the surface mass density and velocity distributions provided by the simulations, taking into account for the first time the asymmetric velocity distribution in the disc. An asteroid disintegrating on an eccentric orbit gives rise to the formation of an asymmetric disc and asymmetric Ca II triplet emission. Our model can explain the periodic reversal of the redshifted and blueshifted peak of the Ca II lines caused by the precession of the disc on timescales of 10.6 to 177.4 days. Our work suggests that the persistence of Ca II asymmetry over decades and its periodic change in the peaks can be explained by asteroids on eccentric orbits in two scenarios. In the first case, the asteroid disrupts on a short timescale (a couple of orbits), and the gas has a low viscosity range ($0.001< to maintain the Ca II signal for decades. In the other scenario, the asteroid disrupts on a timescale of a year, and the viscosity of the gas is required to be high, $

Disc and atmosphere composition of multi-planet systems

In protoplanetary discs, small millimetre-centimetre-sized pebbles drift inwards which can aid in planetary growth and influence the chemical composition of their natal discs. Gaps in protoplanetary discs can hinder the effective inward transport of pebbles by trapping the material in pressure bumps. In this work, we explore how multiple planets change the vapour enrichment by gap opening. For this, we extended the chemcomp code to include multiple growing planets and investigated the effect of 1, 2, and 3 planets on the water content and C/O ratio in the gas disc as well as the final composition of the planetary atmosphere. We followed planet migration over evaporation fronts and found that previously trapped pebbles evaporate relatively quickly and enrich the gas. We also found that in a multi-planet system, the atmosphere composition can be reduced in carbon and oxygen compared to the case without other planets, due to the blocking of volatile-rich pebbles by an outer planet. This effect is stronger for lower viscosities because planets migrate further at higher viscosities and eventually cross inner evaporation fronts, releasing previously trapped pebbles. Interestingly, we found that nitrogen remains super-stellar regardless of the number of planets in the system such that super-stellar values in N/H of giant planet atmospheres may be a tracer for the importance of pebble drift and evaporation.

Learning the Universe: GalactISM Simulations of Resolved Star Formation and Galactic Outflows across Main-sequence and Quenched Galactic Environments

We present a suite of six high-resolution chemodynamical simulations of isolated galaxies, spanning observed disk-dominated environments on the star-forming main sequence, as well as quenched, bulge-dominated environments. We compare and contrast the physics driving star formation and stellar feedback among the galaxies, with a view to modeling these processes in cosmological simulations. We find that the mass loading of galactic outflows is coupled to the clustering of supernova explosions, which varies strongly with the rate of galactic rotation Ω = v circ/R via the Toomre length, leading to smoother gas disks in the bulge-dominated galaxies. This sets an equation of state in the star-forming gas that also varies strongly with Ω, so that the bulge-dominated galaxies have higher midplane densities, lower velocity dispersions, and higher molecular gas fractions than their main-sequence counterparts. The star formation rate in five out of six galaxies is independent of Ω and is consistent with regulation by the midplane gas pressure alone. In the sixth galaxy, which has the most centrally concentrated bulge and thus the highest Ω, we reproduce dynamical suppression of the star formation efficiency in agreement with observations. This produces a transition away from pressure-regulated star formation.

Collisions Between Dark Matter Confined High Velocity Clouds and Magnetized Galactic Disks: The Smith Cloud. II.

We present high-resolution simulations of high velocity clouds (HVCs) colliding with the outer part of the Galactic disk. All of the simulations include a 3 × 108 M ⊙ dark matter subhalo. Three simulations model a dark matter subhalo without a gaseous component, while eight simulations model a dark matter subhalo accompanied by a gaseous cloud of mass 2–8 × 106 M ⊙. Half of the simulations include the coherent component of the Galaxy's magnetic field. Each simulation spans ∼40 million years before the collision and ∼40 million years after the collision. The collisions between the gas cloud and disk splash gas into the halo, punch half-kiloparsec-size holes in the disk, and form long-lived, multi-kiloparsec-size shells. Each shell encloses a bubble of relatively cool gas. Holes and shells of these scales would be observable, and some have been observed in the past. We determine the fate of the HVC gas, temperature, composition, and ionization state of the bubble and shell gas, size and longevity of the holes, and effects of cloud density. Simulations show that the clouds do not survive the chaos of passage through the disk, but instead become part of the splash, bubble, and shell. Some dark matter clouds may appear to carry material with them long after the collision, but this material is shell gas that was captured by the dark matter subhalo. These results have ramifications for the Smith Cloud and other clouds hypothesized to have hit the Galactic disk.

An Edge-on Regular Disk Galaxy at z = 5.289

While rotation-supported gas disks are known to exist as early as at z ≈ 7, it is still a general belief that stellar disks form late in the Universe. This picture is now being challenged by the observations from the James Webb Space Telescope (JWST), which have revealed a large number of disk-like galaxies that could be at z > 3, with some being candidates at z > 7. As an early formation of stellar disks will greatly impact our theory of galaxy formation and evolution, it is important to determine when such systems first emerged. Here we present D-CEERS-RUBIES-z5289 at z = 5.289 ± 0.001, the second confirmed stellar disk at z > 5, discovered using the archival JWST NIRCam imaging and NIRSpec spectroscopic data. This galaxy has a highly regular edge-on disk morphology, extends to ∼6.2 kpc along its major axis, and has an effective radius of ∼1.3–1.4 kpc. Such a large stellar disk is yet to be produced in numerical simulations. By analyzing its 10-band spectral energy distribution using four different tools, we find that it has a high stellar mass of 109.5–10.0 M ⊙. Its age is in the range of 330–510 Myr, and it has a mild star formation rate of 10–30 M ⊙ yr−1. While the current spectroscopic data do not allow the derivation of its rotation curve, the width of its Hα line from the partial slit coverage on one side of the disk reaches ∼345 km s−1, which suggests that it could have a significant contribution from rotation.

A Potential Dynamical Origin of the Galactic Disk Warp: The Gaia–Sausage–Enceladus Major Merger

Previous studies have revealed that the Galactic warp is a long-lived, nonsteady, and asymmetric structure. There is a need for a model that accounts for the warp’s long-term evolution. Given that this structure has persisted for over 5 Gyr, its timeline may coincide with the completion of the Gaia–Sausage–Enceladus (GSE) merger. Recent studies indicate that the GSE, the significant merger of our Galaxy, was likely a gas-rich merger and the large amount of gas introduced could have created a profound impact on the Galactic morphology. This study utilizes GIZMO simulation code to construct a gas-rich GSE merger. By reconstructing the observed characteristics of the GSE, we successfully reproduce the disk warp and capture nearly all of its documented features, which align closely with observational data from both stellar and gas disks. This simulation demonstrates the possibility that a single major merger could generate the Galactic warp amplitude and precession. Furthermore, the analysis of the warp’s long-term evolution may offer more clues into the formation history of the Milky Way.

Morphology of Molecular Clouds at Kiloparsec Scale in the Milky Way: Shear-induced Alignment and Vertical Confinement

The shape of the cold interstellar molecular gas is determined by several processes, including self-gravity, tidal force, turbulence, magnetic field, and galactic shear. Based on the 3D dust extinction map derived by Vergely et al., we identify a sample of 550 molecular clouds within 3 kpc of the solar vicinity in the Galactic disk. Our sample contains clouds whose size ranges from parsec to kiloparsec, which enables us to study the effect of Galactic-scale processes, such as shear, on cloud evolution. We find that our sample clouds follow a power-law mass–size relation of M∝32.00Rmax1.77 , M∝20.59RS2.04 , and M∝14.41RV2.29 , where Rmax is the major axis-based cloud radius, R S is the area-based radius, and R V is the volume-based radius, respectively. These clouds have a mean constant surface density of ∼7 M ⊙ pc−2 and follow a volume density–size relation of ρ∝2.60Rmax−0.55 . As cloud size increases, their shapes gradually transition from ellipsoidal to disk-like to bar-like structures. Large clouds tend to have a pitch angle of 28°−45°, where the angle is measured concerning the Galactic tangential direction. These giant clouds also tend to stay parallel to the Galactic disk plane and are confined within the Galactic molecular gas disk. Our results show that large molecular clouds in the Milky Way can be shaped by Galactic shear and confined in the vertical direction by gravity.

Polar alignment of a dusty circumbinary disc–II. Application to 99 Herculis

ABSTRACT We investigate the formation of dust traffic jams in polar-aligning circumbinary discs. In our first paper, we found as the circumbinary disc evolves towards a polar configuration perpendicular to the binary orbital plane, the differential precession between the gas and dust components leads to multiple dust traffic jams. These dust traffic jams evolve to form a coherent dust ring. In part two, we use 3D smoothed particle hydrodynamical simulations of gas and dust to model an initially highly misaligned circumbinary disc around the 99 Herculis (99 Her) binary system. Our results reveal that the formation of these dust rings is observed across various disc parameters, including the disc aspect ratio, viscosity, surface density power-law index, and temperature power-law index. The dust traffic jams are long-lived and persist even when the disc is fully aligned polar. The midplane dust-to-gas ratio within the rings can surpass unity, which may be a favourable environment for planetesimal formation. Using 2D inviscid shearing box calculations with parameters from our 3D simulations, we find streaming instability modes with significant growth rates. The streaming instability growth time-scale is less than the tilt oscillation time-scale during the alignment process. Therefore, the dust ring will survive once the gas disc aligns polar, suggesting that the streaming instability may aid in forming polar planets around 99 Her.

Sequential formation of supermassive stars and heavy seed BHs through the interplay of cosmological cold accretion and stellar radiative feedback

ABSTRACT Supermassive stars (SMSs) and heavy seed black holes, as their remnants, are promising candidates for supermassive black hole (SMBH) progenitors, especially for ones observed in the early universe $z\simeq 8.5-10$ by recent JWST observations. Expected cradles of SMSs are the atomic cooling haloes ($M_{\rm halo}\simeq 10^7\ \mathrm{M}_{\odot }$), where ‘cold accretion’ emerges and possibly forms SMSs. We perform a suit of cosmological radiation hydrodynamics simulations and investigate star formation after the emergence of cold accretion, solving radiative feedback from stars inside the halo. We follow the mass growth of the protostars for $\sim 3\ \mathrm{Myr}$, resolving the gas inflow down to $\sim 0.1\ \mathrm{pc}$ scales. We discover that, after cold accretion emerges, multiple SMSs of $m_{\star }\gtrsim 10^5\ \mathrm{M}_{\odot }$ form at the halo centre with the accretion rates maintained at $\dot{m}_{\star }\simeq 0.04\ \mathrm{M}_\odot \mathrm{yr}^{-1}$ for $\lesssim 3\ \mathrm{Myr}$. Cold accretion supplies gas at a rate of $\dot{M}_{\rm gas}\gtrsim 0.01-0.1\ \mathrm{M}_\odot \mathrm{yr}^{-1}$ from outside the halo virial radius to the central gas disc. Gravitational torques from spiral arms transport gas further inwards, which feeds the SMSs. Radiative feedback from stars suppresses $\mathrm{H}_2$ cooling and disc fragmentation, while photoevaporation is prevented by a dense envelope, which attenuates ionizing radiation. Our results suggest that cold accretion can bring efficient BH mass growth after seed formation in the later universe. Moreover, cold accretion and gas migration inside the central disc increase the mass concentration and provide a promising formation site for the extremely compact stellar clusters observed by JWST.

N exus: a framework for controlled simulations of idealized galaxies

ABSTRACT Motivated by the need for realistic, dynamically self-consistent, evolving galaxy models that avoid the complexity of full, and zoom-in, cosmological simulations, we have developed Nexus, an integral framework to create and evolve synthetic galaxies made of collisionless and gaseous components. Nexus leverages the power of publicly available, tried-and-tested packages: the stellar-dynamics, action-based library Action-based Galaxy Modelling Architecture (AGAMA); and the adaptive mesh refinement, N-body/hydrodynamical code Ramses, modified to meet our needs. In addition, we make use of a proprietary module to account for galaxy formation physics, including gas cooling and heating, star formation, stellar feedback, and chemical enrichment. Nexus’ basic functionality consists in the generation of bespoke initial conditions (ICs) for a diversity of galaxy models, which are advanced in time to simulate the galaxy’s evolution. The fully self-consistent ICs are generated with a distribution-function-based approach, as implemented in the galaxy modelling module of AGAMA – up to now restricted to collisionless components, extended in this work to treat two types of gaseous configurations: hot haloes and gas discs. Nexus allows constructing equilibrium models with disc gas fractions $0~\le ~f_{\rm {\rm gas}}~\le ~1$, appropriate to model both low- and high-redshift galaxies. Similarly, the framework is ideally suited to the study of galactic ecology, i.e. the dynamical interplay between stars and gas over billions of years. As a validation and illustration of our framework, we reproduce several isolated galaxy model setups reported in earlier studies, and present a new, ‘nested bar’ galaxy simulation. Future upgrades of Nexus will include magnetohydrodynamics and highly energetic particle (‘cosmic ray’) heating.

Origin of transition disk cavities: Pebble-accreting protoplanets vs super-Jupiters

Protoplanetary disks surrounding young stars are the birth places of planets. Among them, transition disks with inner dust cavities of tens of au are sometimes suggested to host massive companions. Yet, such companions are often not detected. Some transition disks exhibit a large amount of gas inside the dust cavity and relatively high stellar accretion rates, which contradicts typical models of gas-giant-hosting systems. Therefore, we investigate whether a sequence of low-mass planets can create the appearance of cavities in the dust disk. We evolve the disks with low-mass growing embryos in combination with 1D dust transport and 3D pebble accretion, to investigate the reduction of the pebble flux at the embryos' orbits. We vary the planet and disk properties to understand the resulting dust profile. We find that multiple pebble-accreting planets can efficiently decrease the dust surface density, resulting in dust cavities consistent with transition disks. The number of low-mass planets necessary to sweep up all pebbles decreases with decreasing turbulent strength and is preferred when the dust Stokes number is $10^ $. Compared to dust rings caused by pressure bumps, those by efficient pebble accretion exhibit more extended outer edges. We also highlight the observational reflections: the transition disks with rings featuring extended outer edges tend to have a large gas content in the dust cavities and rather high stellar accretion rates. We propose that planet-hosting transition disks consist of two groups. In Group A disks, planets have evolved into gas giants, opening deep gaps in the gas disk. Pebbles concentrate in pressure maxima, forming dust rings. In Group B, multiple Neptunes (unable to open deep gas gaps) accrete incoming pebbles, causing the appearance of inner dust cavities and distinct ring-like structures near planet orbits. The morphological discrepancy of these rings may aid in distinguishing between the two groups using high-resolution ALMA observations.

The structure of massive star-forming galaxies from JWST and ALMA: Dusty, high-redshift disc galaxies

We present an analysis of the NIRCam and MIRI morphological and structural properties of 80 massive ($ (M_ M_ odot )$\,=\,11.2\,pm \,0.1) dusty star-forming galaxies at $, identified as sub-millimetre galaxies (SMGs) by ALMA, which have been observed as part of the PRIMER project. To compare the structure of these massive, active galaxies to more typical, less actively star-forming galaxies, we defined two comparison samples. The first of 850 field galaxies matched in specific star formation rate and redshift and the second of 80 field galaxies matched in stellar mass . From the visual classification of the SMGs, we have identified 20\,pm \,5<!PCT!> as candidate late-stage major mergers, a further 40\,pm \,10<!PCT!> as potential minor mergers, and 40\,pm \,10<!PCT!> that have comparatively undisturbed disc-like morphologies, with no obvious massive neighbours on lesssim \,20\,--\,30\,kpc (projected) scales. These rates are comparable to those for the field samples and indicate that the majority of the sub-millimetre-detected galaxies are not late-stage major mergers, but have interaction rates similar to the general field population at $z$\,sim \,2--3. Through a multi-wavelength morphological analysis, using parametric and non-parametric techniques, we establish that SMGs have comparable near-infrared, mass-normalised sizes to the less active population, $ F444W $\,=\,2.7\,pm \,0.2\,kpc versus $ F444W $\,=\,3.1\,pm \,0.1\,kpc, but exhibit lower S\'ersic indices, consistent with bulge-less discs: F444W $\,=\,1.1\,pm \,0.1, compared to F444W $\,=\,1.9\,pm \,0.1 for the less active field galaxies and $n_ F444W $\,=\,2.8\,pm \,0.2 for the most massive field galaxies . The SMGs exhibit greater single-S\'ersic fit residuals and their morphologies are more structured at 2 relative to 4 when compared to the field galaxies. This appears to be caused by significant structured dust content in the SMGs and we find evidence for dust reddening as the origin of the morphological differences by identifying a strong correlation between the F200W$-$F444W pixel colour and the 870 surface brightness using high-resolution ALMA observations. We conclude that SMGs and both massive and less massive star-forming galaxies at the same epochs share a common disc-like structure, but the weaker bulge components (and potentially lower black hole masses) of the SMGs result in their gas discs being less stable. Consequently, the combination of high gas masses and instabilities triggered either secularly or by minor external perturbations results in higher levels of activity (and dust content) in SMGs compared to typical star-forming galaxies.

Using meteorite magnetism to elucidate early solar system history – MMESSH

Using meteorite magnetism to elucidate early solar system history – MMESSH By utilising several recent breakthroughs in extraterrestrial magnetism, MMESSH aims to unlock pivotal insights into the protoplanetary disk of dust and gas that surrounded the young Sun. Because the behaviour of this disk underpinned the process of planet building, this project has the potential to revolutionise our understanding of the formation and habitability of the Earth.

Unveiling accretion in the massive young stellar object G033.3891

Context. The inner parts of the hot discs surrounding massive young stellar objects (MYSOs) are still barely explored due to observational limitations in terms of angular resolution, scarcity of diagnostic lines, and the embedded and rare nature of these targets. Aims. We present the first K-band spectro-interferometric observations towards the MYSO G033.3891, which based on former kinematic evidence via the CO bandhead emission is known to host an accreting disc. Methods. Using the high spectral resolution mode (R∼4000) of the GRAVITY/VLTI, we spatially resolved the emission of the inner dusty disc and the crucial gaseous interface between the star and the dusty disc. Using detailed modelling on the K-band dust continuum and tracers known to be associated with the ionised and molecular gaseous interface (Brγ, CO), we report on the smallest scales of accretion and ejection. Results. The new observations in combination with our geometric and kinematic models employed to fit former high spectral resolution observations on the source (R∼30 000; CRIRES/VLTI) allowed us to constrain the size of the inner gaseous disc both spatially and kinematically via the CO overtone emission at only 2 au. Our models reveal that both Brγ and CO emissions are located well within the dust sublimation radius (5 au) as traced by the hot 2.2 µm dust continuum. Conclusions. Our paper provides the first case study where the tiniest scales of gaseous accretion around the MYSO G033.3891 are probed both kinematically and spatially via the CO bandhead emission. This analysis of G033.3891 stands as only the second instance of such an investigation within MYSOs, underscoring the gradual accumulation of knowledge regarding how massive young stars gain their mass while further solidifying the disc nature of accretion at the smallest scales of MYSOs.

A Close Pair of Orbiters Embedded in a Gaseous Disk: The Repulsive Effect

We develop a theoretical framework and use 2D hydrodynamical simulations to study the repulsive effect between two close orbiters embedded in an accretion disk. We consider orbiters on fixed Keplerian orbits with masses low enough to open shallow gaps. The simulations indicate that the repulsion is larger for more massive orbiters and decreases with the orbital separation and the disk’s viscosity. We use two different assumptions to derive theoretical scaling relations for the repulsion. A first scenario assumes that each orbiter absorbs the angular momentum deposited in its horseshoe region by the companion’s wake. A second scenario assumes that the corotation torques of the orbiters are modified because the companion changes the underlying radial gradient of the disk surface density. We find a substantial difference between the predictions of these two scenarios. The first one fails to reproduce the scaling of the repulsion with the disk viscosity and generally overestimates the strength of the repulsion. The second scenario, however, gives results that are broadly consistent with those obtained in the simulations.

Spectral Transformation Detection in Be Stars Using Multi-Parameters Analysis of Delta Scorpii, Eta Centauri, and Kappa Lupi

Abstract Over the past five years, the Bosscha Observatory in Bandung, Indonesia, has dedicated significant attention to studying B-emission (Be) stars exhibiting distinctive emission characteristics. In this work, we meticulously analyzed the spectra originating from three prominent Be stars: Delta Scorpii, Eta Centauri, and Kappa Lupi. We also took additional spectrum data from the BeSS repository for each of the three stars to maximize our analysis results. Our analysis revolved around quantifying crucial spectral attributes, including the emission peak centers, the equivalent width (EW), and the full width at half maximum (FWHM). These parameters proved pivotal for deriving the violet-to-red peak intensity ratio (V/R), emission-to-continuum ratio (E/C), and the star’s radial velocity. Based on our analysis, there are several things to be pointed out. For all stars, there was no such significant variation in E/C values. Our single-peak analysis of δ Sco showed a strong emission primarily caused by the presence of a circumstellar disk of gas. FWHM of Hα in κ Lup demonstrated minor variability with time, meanwhile FWHM of Hα in η Cen decreased with time and orbital phase. Much more intense observations and analysis should provide better data to conclude the variability pattern of those parameters.

Measuring 60 pc-scale Star Formation Rate of the Nearby Seyfert Galaxy NGC 1068 with ALMA, HST, VLT/MUSE, and VLA

The star formation rate (SFR) is a fundamental parameter for describing galaxies and inferring their evolutionary course. H ii regions yield the best measure of instantaneous SFR in galaxies, although the derived SFR can have large uncertainties depending on tracers and assumptions. We present an SFR calibration for the entire molecular gas disk of the nearby Seyfert galaxy NGC 1068, based on our new high-sensitivity Atacama Large Millimeter/submillimeter Array 100 GHz continuum data at 55 pc (= 0.″8) resolution in combination with the Hubble Space Telescope Paα line data. In this calibration, we account for the spatial variations of dust extinction, electron temperature of H ii regions, AGN contamination, and diffuse ionized gas (DIG) based on publicly available multiwavelength data. Especially, given the extended nature and the possible nonnegligible contribution to the total SFR, a careful consideration of DIG is essential. With a cross-calibration between two corrected ionized gas tracers (free–free continuum and Paα), the total SFR of the NGC 1068 disk is estimated to be 3.2 ± 0.5 M ⊙ yr−1, one-third of the SFR without accounting for DIG (9.1 ± 1.4 M ⊙ yr−1). We confirmed a high SFR around the southern bar end and the corotation radius, which is consistent with the previous SFR measurements. In addition, our total SFR exceeds the total SFR based on 8 μm dust emission by a factor of 1.5. We attribute this discrepancy to the differences in the young stars at different stages of evolution traced by each tracer and their respective timescales. This study provides an example to address the various uncertainties in conventional SFR measurements and their potential to lead to significant SFR miscalculations.

Multistructured Accretion Flow of Sgr A*. II. Signatures of a Cool Accretion Disk in Hydrodynamic Simulations of Stellar Winds

Hydrodynamic simulations of the stellar winds from Wolf–Rayet stars within the Galactic center can provide predictions for the X-ray spectrum of the supermassive black hole Sgr A*. Herein, we present results from updated smooth particle hydrodynamics simulations, building on the architecture of Cuadra et al. and Russell et al., and find that a “cold” (104 K) gas disk forms around Sgr A* with a simulation runtime of 3500 yr. This result is consistent with previous grid-based simulations, demonstrating that a cold disk can form regardless of numerical method. We examine the plasma scenarios arising from an environment with and without this cold disk, by generating synthetic spectra for comparison to the quiescent Fe Kα Sgr A* spectrum from Chandra HETGS, taken through the Chandra X-ray Visionary Program. We find that current and future X-ray missions are unlikely to distinguish between the kinematic signatures in the plasma in these two scenarios. Nonetheless, the stellar wind plasma model presents a good fit to the dispersed Chandra spectra within 1.″5 of Sgr A*. We compare our results to the radiatively inefficient accretion flow (RIAF) model fit to the HETGS spectrum presented in Paper I and find that the Bayesian model evidence does not strongly favor either model. With 9″ angular resolution and high spectral resolution of the X-IFU, NewAthena will offer a clearer differentiation between the RIAF plasma model and hydrodynamic simulations, but only a future X-ray mission with arcsecond resolution will significantly advance our understanding of Sgr A*’s accretion flow in X-rays.