Radiation Hydrodynamic Simulations Research Articles

The thesan project: Connecting ionized bubble sizes to their local environments during the Epoch of Reionization

Abstract An important characteristic of cosmic hydrogen reionization is the growth of ionized gas bubbles surrounding early luminous objects. Ionized bubble sizes are beginning to be probed using Lyman-α emission from high-redshift galaxies, and will also be probed by upcoming 21-cm maps. We present results from a study of bubble sizes using the state-of-the-art thesan radiation-hydrodynamics simulation suite, which self-consistently models radiation transport and realistic galaxy formation. We employ the mean-free path method, and track the evolution of the effective ionized bubble size at each point (Reff) throughout the Epoch of Reionization. We show there is a slow growth period for regions ionized early, but a rapid ‘flash ionization’ process for regions ionized later as they immediately enter a large, pre-existing bubble. We also find that bright sources are preferentially in larger bubbles, and find consistency with recent observational constraints at z ≳ 9, but tension with idealized Lyman-α damping-wing models at z ≈ 7. We find that high overdensity regions have larger characteristic bubble sizes, but the correlation decreases as reionization progresses, likely due to runaway formation of large percolated bubbles. Finally, we compare the redshift at which a region transitions from neutral to ionized (zreion) with the time it takes to reach a given bubble size and conclude that zreion is a reasonable local probe of small-scale bubble size statistics ($R_\text{eff} \lesssim 1\, \rm {cMpc}$). However, for larger bubbles, the correspondence between zreion and size statistics weakens due to the time delay between the onset of reionization and the expansion of large bubbles, particularly at high redshifts.

The Interplay between the Initial Mass Function and Star Formation Efficiency through Radiative Feedback at High Stellar Surface Densities

The observed rest-UV luminosity function at cosmic dawn (z ∼ 8–14) measured by JWST revealed an excess of UV-luminous galaxies relative to many prelaunch theoretical predictions. A high star formation efficiency (SFE) and a top-heavy initial mass function (IMF) are among the mechanisms proposed for explaining this excess. Although a top-heavy IMF has been proposed for its ability to increase the light-to-mass ratio (ΨUV), the resulting enhanced radiative pressure from young stars could decrease the SFE, potentially driving galaxy luminosities back down. In this Letter, we use idealized radiation hydrodynamic simulations of star cluster formation to explore the effects of a top-heavy IMF on the SFE of clouds typical of the high-pressure conditions found at these redshifts. We find that the SFE in star clusters with solar-neighborhood-like dust abundance decreases with increasingly top-heavy IMFs—by ∼20% for an increase of a factor of 4 in ΨUV and by 50% for a factor of ∼10 in ΨUV. However, we find that an expected decrease in the dust-to-gas ratio (∼0.01 × solar) at these redshifts can completely compensate for the enhanced light output. This leads to a (cloud-scale; ∼10 pc) SFE that is ≳70% even for a factor of 10 increase in ΨUV, implying that highly efficient star formation is unavoidable for high surface density and low-metallicity conditions. Our results suggest that a top-heavy IMF, if present, likely coexists with efficient star formation in these galaxies.

The development of thermodynamically consistent and physics-informed equation-of-state model through machine learning

Ab initio molecular dynamics (AIMD) simulations have become an important tool used in the construction of equations of state (EOS) tables for warm dense matter. Due to computational costs, only a limited number of system state conditions can be simulated, and the remaining EOS surface must be interpolated for use in radiation-hydrodynamic simulations of experiments. In this work, we develop a thermodynamically consistent EOS model that utilizes a physics-informed machine learning approach to implicitly learn the underlying Helmholtz free-energy from AIMD generated energies and pressures. The model, referred to as PIML-EOS, was trained and tested on warm dense polystyrene producing a fit within a 1% relative error for both energy and pressure and is shown to satisfy both the Maxwell and Gibbs–Duhem relations. In addition, we provide a path toward obtaining thermodynamic quantities, such as the total entropy and chemical potential (containing both ionic and electronic contributions), which are not available from current AIMD simulations.

Peering into cosmic reionization: Ly alpha visibility evolution from galaxies at z = 4.5 - 8.5 with JWST

The resonant scattering interaction between photons and neutral hydrogen implies that a partially neutral intergalactic medium has the ability to significantly impact the detectability of emission in galaxies. Thus, the redshift evolution of the equivalent width distribution of galaxies offers a key observational probe of the degree of ionization during the Epoch of Reionization (EoR). Previous in-depth investigations at $z$ geq 7 were limited by ground-based instrument capabilities. We present an extensive study of the evolution of emission from galaxies at 4.5 < $z$ < 8.5, observed as part of the CEERS and JADES surveys in the JWST NIRSpec/PRISM configuration. The sample consists of 235 galaxies in the redshift range of 4.1 < $z$ < 9.9. We identified 65 of them as emitters. We first measured the escape fractions from to Balmer line flux ratios and explored the correlations with the inferred galaxies' physical properties, which are similar to those found at lower redshift. We also investigated the possible connection between the escape of photons and the inferred escape fractions of LyC photons obtained from indirect indicators, finding no secure correlation. We then analyzed the redshift evolution of the emitter fraction, finding lower average values at $z$ = 5 and 6 compared to previous ground-based observations. At $z$ = 7, the GOODS-S results are aligned with previous findings, whereas the visibility in the EGS field appears to be enhanced. This discrepancy in visibility between the two fields could potentially be attributed to the presence of early reionized regions in the EGS. Such a broad variance is also expected in the Cosmic Dawn II radiation-hydrodynamical simulation. The average emitter fraction obtained from the CEERS+JADES data continues to increase from $z$ = 5 to 7, ultimately declining at $z$ = 8. This suggests a scenario in which the ending phase of the EoR is characterized by sim 1 pMpc ionized bubbles around a high fraction of moderately bright galaxies. Finally, we characterize such two ionized regions found in the EGS at $z$ = 7.18 and $z$ = 7.49 by estimating the radius of the ionized bubble that each of the spectroscopically-confirmed members could have created.

Formation of low-mass protostars and their circumstellar disks

Understanding circumstellar disks is of prime importance in astrophysics; however, their birth process remains poorly constrained due to observational and numerical challenges. Recent numerical works have shown that the small-scale physics, often wrapped into a sub-grid model, play a crucial role in disk formation and evolution. This calls for a combined approach in which both the protostar and circumstellar disk are studied in concert. We aim to elucidate the small-scale physics and constrain sub-grid parameters commonly chosen in the literature by resolving the star-disk interaction. We carried out a set of very high resolution 3D radiative-hydrodynamics simulations that self-consistently describe the collapse of a turbulent, dense molecular cloud core to stellar densities. We studied the birth of the protostar, the circumstellar disk, and its early evolution ($<6\ yr $ after protostellar formation). Following the second gravitational collapse, the nascent protostar quickly reaches breakup velocity and sheds its surface material, thus forming a hot ($ K $), dense, and highly flared circumstellar disk. The protostar is embedded within the disk such that material can flow without crossing any shock fronts. The circumstellar disk mass quickly exceeds that of the protostar, and its kinematics are dominated by self-gravity. Accretion onto the disk is highly anisotropic, and accretion onto the protostar mainly occurs through material that slides on the disk surface. The polar mass flux is negligible in comparison. The radiative behavior also displays a strong anisotropy, as the polar accretion shock was shown to be supercritical, whereas its equatorial counterpart is subcritical. We also find a remarkable convergence of our results with respect to initial conditions. These results reveal the structure and kinematics in the smallest spatial scales relevant to protostellar and circumstellar disk evolution. They can be used to describe accretion onto regions commonly described by sub-grid models in simulations studying larger-scale physics.

Highly-mass-loaded hot galactic winds are unstable to cool filament formation

Abstract As cool clouds are entrained by a hot supersonic galactic wind, they may be shredded by hydrodynamical instabilities and incorporated into the hot flow. One-dimensional steady-state calculations show how cool cloud entrainment affects the bulk thermodynamics and kinematics of the hot gas: mass-loading decelerates the hot flow and changes its entropy. Here, we investigate the stability of mass-loaded hot winds using both perturbation analysis and 3D time-dependent radiative hydrodynamical simulations. We show that mass-loading is stable over a broad range of parameters and that the 1D time-steady analytic solutions exactly reproduce the 3D time-dependent calculations, provided that the flow does not decelerate sufficiently to become subsonic. For higher values of the mass-loading, the flow develops a second sonic point, with the first being at the edge of the wind-driving region. Strong deceleration increases the wind density and the flow becomes radiative, undergoing a thermal instability to form elongated dense cometary filaments. We explore the mass-loading parameters required to trigger this behavior. For certain approximations, we can derive analytic criteria. In general a mass-loading rate similar to the initial hot mass outflow rate is required. In this sense, the destruction of small cool clouds by a hot flow may ultimately spontaneously generate fast cool filaments, as observed in starburst winds. Lastly, we find that the kinematics of filaments is sensitive to the slope of the mass-loading function. Filaments move faster than the surrounding wind if mass-loading is over long distances whereas filaments move slower than their surroundings if mass-loading is abrupt.

Inverse design of the radiation temperature for indirect laser-driven equation-of-state measurement

The theoretical design for the time profile of radiation temperature plays an important role in indirect laser-driven equation-of-state measurement, which severely relies on a large number of radiation hydrodynamic simulations. In this work, we provide a concise data-driven method for optimizing the radiation temperature profile, which combines a time-varying Volterra model with an improvement achieved by data generation via radiation hydrodynamic simulations utilizing random perturbations in a skew normal distribution as inputs. We find that the time-varying Volterra model can be used to investigate the time-dependent relationship between the radiation temperature and the key physical quantities of interest, such as shock-wave velocity and ablation drive pressure. With this method, we realize the inverse designs of the radiation temperature profiles for planar dynamic shock and ramp compressions according to the desired shock-wave velocity and drive pressure, respectively, which shows the advantage of practical application in experiments.

Effects of drive pulse shape on graded metal pushered single shell capsule implosions on the National Ignition Facility

Graded metal pushered single shells (PSS) are a viable alternative to low-Z capsules (Z is the atomic number) for indirect drive inertial confinement fusion implosions due to enhanced core tamping and radiation trapping, but they can be compromised by the pusher mixing with the fuel. We compare 2-shock and 3-shock laser pulses for Be/Cr PSS capsules filled with deuterium–tritium gas fuel at 6 mg/cc density. 1D radiation-hydrodynamic simulations predict higher core compression and, hence, ∼2× higher fusion yield for the 3-shock drive than for 2-shock. Nevertheless, we observe similar core ion temperatures and fusion yields for both drives. The implosion burn duration is 25% shorter and the core volume is ∼2.5× smaller for the 3-shock drive than for 2-shock, consistent with a higher compression. 1D LASNEX mix simulations using a buoyancy-drag model matching the measured yields also agree with the observed core sizes and burn durations and suggest ∼40% and ∼70% yield degradations for 2-shock and 3-shock drives due to hydrodynamic instabilities and atomic mix at the pusher–fuel interface. At the same time, 2D HYDRA simulations show that mid-mode (2–250) instability degradations are negligible for the 2-shock implosion (9%) and significant (45%) for 3-shock. Subtracting these from the 1D mix simulations, we infer similar degradations from high-mode instabilities and atomic mix for both drives. Due to its robustness to mid-mode instabilities, future pusher–gas mix studies will use the 2-shock drive.

Analysis of extreme ultraviolet radiation and hydrodynamics simulation at the core of laser-produced nickel plasmas

The non-uniformity and transient nature of laser-produced plasma are critical factors that affect the analysis of the extreme ultraviolet spectra of highly charged ions and the diagnosis of plasma states. This paper systematically investigates the characteristics of extreme ultraviolet radiation and the hydrodynamic evolution of laser-produced nickel plasmas from two perspectives: high-spatio-temporal-resolution extreme-ultraviolet spectroscopic measurement and radiation hydrodynamics simulation. The consistency between the four-band experimental spectra and their theoretically simulated spectra confirms the accuracy of the atomic structure parameters and plasma state parameters. We also analyze the significant contribution of the 3d-4f double-excited state radiation to the spectral profile and discuss the influence of the self-absorption caused by plasma opacity on the characteristics of extreme ultraviolet radiation. The findings are crucial for accurately understanding the characteristics of extreme ultraviolet radiation, the hydrodynamic evolution, and the application of medium- and high-Z laser-produced plasma as a pulsed short-wavelength light source.

Acceleration mechanisms of energetic ion debris in laser-driven tin plasma EUV sources

Laser-driven tin plasmas are driving new-generation nanolithography as sources of extreme ultraviolet (EUV) radiation centered at 13.5 nm. A major challenge facing industrial EUV source development is predicting energetic ion debris produced during the plasma expansion that may damage the sensitive EUV channeling multilayer optics. Gaining a detailed understanding of the plasma dynamics and ion acceleration mechanisms in these sources could provide critical insights for designing debris mitigation strategies in future high-power EUV sources. We develop a fully kinetic model of tin-EUV sources using one-dimensional particle-in-cell simulations to study ion debris acceleration, which will be valuable for cross-validation of radiation-hydrodynamic simulations. An inverse-bremsstrahlung heating operator is used to model the interaction of a tin target with an Nd:YAG laser, and thermal conduction is included through a Monte Carlo Coulomb collision operator. While the large-scale evolution is in reasonable agreement with analogous hydrodynamic simulations, the significant timescale for collisional equilibration between electrons and ions allows for the development of prominent two-temperature features. A collimated flow of energetic ions is produced with a spectrum that is significantly enhanced at high energies compared to fluid simulations. The dominant acceleration mechanism is found to be a large-scale electric field supported mainly by the electron pressure gradient, which is enhanced in the kinetic simulations due to the increased electron temperature. We discuss the implications of these results for future modeling of tin-EUV sources and the development of debris mitigation schemes.

Impact of radiative feedback on the initial mass function of metal-poor stars

ABSTRACT The stellar initial mass function (IMF) in the early universe is essential to understand the formation of ancient galaxies. To this end, we conduct a series of long-term radiation hydrodynamic simulations following star cluster formation, varying the metallicity from Z/Z⊙ = 10−4 to 1. We particularly consider the effects of protostellar radiative feedback, which modify the exact shape of the IMF and determine the star formation efficiency (SFE), i.e. the ratio between the mass in stars and the initial gas mass in the parental cloud. Our results show that the IMF changes from a Salpeter-type to a top-heavy function as the metallicity decreases. When Z/Z⊙ ≲ 10−2, the IMF becomes log-flat and distinct from a Salpeter-like IMF. Stellar feedback is effective in shaping both the low- and high-mass ends of the IMF. Heating of dust grains by stellar radiation suppresses small-scale fragmentation and reduces the number of low-mass stars with M* ≲ 1 M⊙ at all metallicities. The ionizing radiation hinders the growth of massive stars, steepening the slope of the IMF at the high-mass end. The resulting feedback is more effective at lower metallicity, and star formation is regulated by stellar radiative feedback, with the SFE decreasing with decreasing metallicity. We suggest that the unexpectedly large number of UV-bright galaxies at z > 10 reported by JWST observations can be explained by considering star cluster formation at Z/Z⊙ ∼ 10−2 or 10−3, where the IMF is top-heavy, but the SFE is not too low due to stellar feedback.

The impact of low-mode symmetry on inertial fusion energy output in the burning plasma state

Indirect Drive Inertial Confinement Fusion Experiments on the National Ignition Facility (NIF) have achieved a burning plasma state with neutron yields exceeding 170 kJ, roughly 3 times the prior record and a necessary stage for igniting plasmas. The results are achieved despite multiple sources of degradations that lead to high variability in performance. Results shown here, for the first time, include an empirical correction factor for mode-2 asymmetry in the burning plasma regime in addition to previously determined corrections for radiative mix and mode-1. Analysis shows that including these three corrections alone accounts for the measured fusion performance variability in the two highest performing experimental campaigns on the NIF to within error. Here we quantify the performance sensitivity to mode-2 symmetry in the burning plasma regime and apply the results, in the form of an empirical correction to a 1D performance model. Furthermore, we find the sensitivity to mode-2 determined through a series of integrated 2D radiation hydrodynamic simulations to be consistent with the experimentally determined sensitivity only when including alpha-heating.

2D unified atmosphere and wind simulations of O-type stars

Context. Massive and luminous O-type star (O star) atmospheres with winds have been studied primarily using one-dimensional (1D), spherically symmetric, and stationary models. However, observations and theory have suggested that O star atmospheres are highly structured, turbulent, and time-dependent. As such, when making comparisons to observations, present-day 1D modeling tools require the introduction of ad hoc quantities such as photospheric macro- and microturbulence, wind clumping, and other relevant properties. Aims. We present a series of multi-dimensional, time-dependent, radiation-hydrodynamical (RHD) simulations for O stars that encapsulate the deeper sub-surface envelope (down to T ~ 450 kK), as well as the supersonic line-driven wind outflow in one unified approach. Our overarching aim is to develop a framework that is free from the ad-hoc prescriptions that plague present-day 1D models. Here, we start with an analysis of a small set of such multi-dimensional simulations and then compare them to atmospheric structures predicted by their 1D counterparts. Methods. We performed time-dependent, two-dimensional (2D) simulations of O star atmospheres with winds using a flux-limiting RHD finite volume modelling technique. Opacities are computed using a hybrid approach combining tabulated Rosseland means with calculations (based on the Sobolev approximation) of the enhanced line opacities expected for supersonic flows. The initial conditions and comparison models were derived using similar procedures as those applied in standard 1D stationary model atmosphere with wind codes. Results. Structure starts appearing in our simulations just below the iron-opacity peak at ~200 kK. Local pockets of gas with radiative accelerations that exceed gravity then shoot up from these deep layers into the upper atmosphere, where they interact with the line-driven wind outflow initiated around or beyond the variable photosphere. This complex interplay creates large turbulent velocities in the photospheric layers of our simulations, on the order of ~30–100km s−1, with higher values for models with higher luminosity-to-mass ratios. This offers a generally good agreement with observations of large photospheric ‘macroturbulence’ in O stars. When compared to 1D models, the average structures in the 2D simulations display less envelope expansion and no sharp density-inversions, along with density and temperature profiles that are significantly less steep around the photosphere, and a strong anti-correlation between velocity and density in the supersonic wind. Although the wind initiation region is complex and highly variable in our simulations, our average mass-loss rates agree well with stationary wind models computed by means of full co-moving frame radiative transfer solutions. Conclusions. The different atmospheric structures found in 2D and 1D simulations are likely to affect the spectroscopic determination of fundamental stellar and wind parameters for O stars as well as the empirical derivation of their chemical abundance patterns. To qualitatively match the different density and temperature profiles seen in our multi-dimensional and 1D models, we need to add a modest amount of convective energy transport in the deep sub-surface layers and a large turbulent pressure around the photosphere to the 1D models.

Thick-shell model of indirect-drive yield sensitivity

We present an analytic thick shell model for indirect-drive ICF implosions that starts by using the Rocket equation to evaluate peak fuel kinetic energy and hence by energy balance, stagnated fuel internal energy. We then use the approximation of the hot spot decelerating adiabatically to an isobaric stagnated state coupled to a self-consistently calculated fuel aspect ratio. The model, validated by 1D radiation-hydrodynamics simulations, provides sensitivities of indirect-drive yield, DSR and ignition metrics to a host of initial and final state capsule and hohlraum parameters, applicable to the current relevant regime of igniting implosions. The model is used to highlight parameter trade-offs and estimate expected sensitivity in 1D compression, stagnated areal density and yield at current and higher performance levels. Several new insights are presented. Of note, we explain the weak dependence of ablator thickness on implosion velocity for designs with buried dopant layers, the uncertainty in performance improvement when adding fuel or reducing initial hot spot density, and the role of ionization energy and albedo in setting ablator efficiency.

The Physics of Indirect Estimators of Lyman Continuum Escape and their Application to High-Redshift JWST Galaxies

ABSTRACT Reliable indirect diagnostics of LyC photon escape from galaxies are required to understand which sources were the dominant contributors to reionization. While multiple LyC escape fraction (fesc) indicators have been proposed to trace favourable conditions for LyC leakage from the interstellar medium of low-redshift ‘analogue’ galaxies, it remains unclear whether these are applicable at high redshifts where LyC emission cannot be directly observed. Using a library of 14 120 mock spectra of star-forming galaxies with redshifts 4.64 ≤ z ≤ 10 from the SPHINX20 cosmological radiation hydrodynamics simulation, we develop a framework for the physics that leads to high fesc. We investigate LyC leakage from our galaxies based on the criteria that successful LyC escape diagnostics must (i) track a high-specific star formation rate, (ii) be sensitive to stellar population age in the range 3.5–10 Myr representing the times when supernova first explode to when LyC production significantly drops, and (iii) include a proxy for neutral gas content and gas density in the interstellar medium. O32, ΣSFR, MUV, and H β equivalent width select for one or fewer of our criteria, rendering them either necessary but insufficient or generally poor diagnostics. In contrast, UV slope (β), and E(B − V) match two or more of our criteria, rendering them good fesc diagnostics (albeit with significant scatter). Using our library, we build a quantitative model for predicting fesc based on direct observables. When applied to bright z > 6 Ly α emitters observed with JWST, we find that the majority of them have $f_{\rm esc} \lesssim 10~{{\ \rm per\ cent}}$.

Space-time dependent non-local thermal transport effects on laser ablation dynamics in inertial confinement fusion

In inertial confinement fusion (ICF), electron thermal transport plays a key role in laser ablation and the subsequent implosion processes, which always exhibits intractable non-local effects. Simple modifications of the local Spitzer–Härm model with either an artificially-assumed constant flux limiter or a purely time-dependent one are applied to explain some experimental data, but fail to simultaneously reproduce the space-time evolution of the whole laser ablation process. Here, by carrying out a series of one-dimensional and two-dimensional radiation hydrodynamic simulations where the space-time-dependent non-local thermal transport model proposed by Schurt, Nicolaï and Busquet (the SNB model) are self-consistently included, we systematically study the non-local effects on the whole laser ablation dynamics including those occurring at the critical surface, the conduction zone and the ablation front. Different from those obtained previously, our results show that due to the non-local heat flow redistribution and redirection, at the critical surface the thermal flux is more inhibited, in the conduction zone the lateral thermal transport is suppressed, and ahead of the ablation front the plasma is preheated. When combined together they eventually result in significant improvement of the laser absorption efficiency, extension of the conduction zone, increase of both the mass ablation rate and shock velocity. Furthermore, the dependence of these laser ablation dynamics on different drive laser intensities is investigated, which provides beneficial enlightenments on potential laser pulse shaping and/or ignition scheme optimization in ICF.

Explaining the high nitrogen abundances observed in high-z galaxies via population III stars of a few thousand solar masses

The chemical enrichment of the early Universe is a crucial element in the formation and evolution of galaxies, and Population III (Pop III) stars must play a vital role in this process. In this study, we examine metal enrichment from massive stars in the early Universe’s embryonic galaxies. Using radiation hydrodynamic simulations and stellar evolution modelling, we calculated the expected metal yield from these stars. Specifically, we applied accretion rates from a previous radiation-hydrodynamic simulation to inform our stellar evolution modelling, executed with the Geneva code, across 11 selected datasets, with final stellar masses between 500 and 9000 M⊙. Our results demonstrate that the first generation of Pop III stars within a mass range of 2000−9000 M⊙ result in N/O, C/O and O/H ratios compatible with the values observed in very high-z galaxies GN-z11 and CEERS 1019. The ejecta of these Pop III stars are predominantly composed of 4He, 1H, and 14N. Our Pop III chemical enrichment model of the halo can accurately reproduce the observed N/O and C/O ratios, and, by incorporating a hundred times more zero-metallicity interstellar material with the stellar ejecta, it accurately attains the observed O/H ratio. Thus, a sub-population of extremely massive Pop III stars, with masses surpassing approximately 2000 M⊙, effectively reproduces the CNO elemental abundances observed in high-z JWST galaxies to date. We closely reproduced the observed Ne/O ratio in CEERS 1019 employing a model with several thousand solar masses and non-zero metallicity, and we projected a 12C/13C ratio of 7, substantially lower than the solar ratio of around 90. The significant nitrogen enrichment predicted by Pop III stars with a few thousand solar masses not only reinforces the argument for a heavy seed formation pathway for massive black holes at redshifts as high as z = 10.6 but it also accentuates the need for deeper investigations into their complex nature and pivotal role in the early Universe.

Effects of Kelvin–Helmholtz instability on the material mixing in the double-cone ignition

The Kelvin–Helmholtz instability (KHI) occurs on the interface of gold cones and embedded fuels for fusion schemes with gold cones. The development of KHI on the inner surface of gold cones in the double-cone ignition scheme is investigated with two-dimensional radiation hydrodynamic simulations. It has been found that the colliding high-density fuel plasma between the tips of the two cones is spatiotemporally separated from the mixed gold ions from the inner surface of the gold cones due to the KHI. Furthermore, it is found that fuel layers coated on the inner surface of the cones can effectively mitigate the energy loss in the compression process. These results could provide a reference for fast ignition schemes with gold cones.

The Effect of Ultraviolet Photon Pumping of H2 in Dust-deficient Protoplanetary Disks

We perform radiation hydrodynamics simulations to study the structure and evolution of a photoevaporating protoplanetary disk. Ultraviolet and X-ray radiation from the host star heats the disk surface, where H2 pumping also operates efficiently. We run a set of simulations in which we varied the number of dust grains or the dust-to-gas mass ratio, which determines the relative importance between photoelectric heating and H2 pumping. We show that H2 pumping and X-ray heating contribute more strongly to the mass loss of the disk when the dust-to-gas mass ratio is D≤10−3 . The disk mass-loss rate decreases with a lower dust amount, but remains around 10−10−11 M ⊙yr−1. In these dust-deficient disks, H2 pumping enhances photoevaporation from the inner disk region and shapes the disk mass-loss profile. We thus argue that the late-stage disk evolution is affected by the ultraviolet H2 pumping effect. The mass-loss rates derived from our simulations can be used in the study of long-term disk evolution.

How Population III Supernovae Determined the Properties of the First Galaxies

Massive Population III stars can die as energetic supernovae that enrich the early Universe with metals and determine the properties of the first galaxies. With masses of about 109 M ⊙ at z ≳ 10, these galaxies are believed to be the ancestors of the Milky Way. This paper investigates the impact of Population III supernova remnants (SNRs) from both Salpeter-like and top-heavy initial mass functions (IMFs) on the formation of first galaxies with high-resolution radiation-hydrodynamical simulations with the ENZO code. Our findings indicate that SNRs from a top-heavy Population III IMF produce more metals, leading to more efficient gas cooling and earlier Population II star formation in the first galaxies. From a few hundred to a few thousand Population II stars can form in the central regions of these galaxies. These stars have metallicities of 10−3–10−2, Z ⊙, greater than those of extremely metal-poor (EMP) stars. Their mass function follows a power-law distribution with dN(M*)/dM*∝M*α , where M * is stellar mass, and α = 2.66–5.83 and is steeper for a top-heavy IMF. We thus find that EMP stars were not typical of most primitive galaxies.