arXiv subjects

Richard Wünsch

Publications and source records attributed to Richard Wünsch.

At least 19 recordsLinked to original sources

arXiv2026

X-rays from shock-heated gas in recurrent-nova remnants: Nested nova shells in a structured circumstellar medium

Recurrent symbiotic novae such as RS Oph show extended X-ray emission associated with the interaction of nova ejecta with the circumstellar environment. We investigate how repeated eruptions over more than a century structure the circumstellar medium and govern the long-term X-ray evolution of a symbiotic recurrent nova. We perform three-dimensional hydrodynamical simulations for a fiducial nine-eruption sequence spanning 130 years, modeling each nova as a supersonic bipolar shell expanding into a wind-shaped circumstellar medium. We post-process the resulting density and temperature distributions to compute X-ray emission in the 0.5-2.0 and 2.0-10.0 keV bands. The eruption sequence excavates a bipolar cavity bounded by nested shells. Soft X-rays trace dense compressed interfaces, whereas hard X-rays arise from the hottest shocked gas, including shell rims and the excavated nova-remnant interior. As the remnant expands, the soft-band emission shows a gradual long-term decline associated with the decreasing emission measure. The hard band evolves episodically, with individual eruptions imprinting distinct flares whose timing and relative strength change as the shell system grows. The extended X-ray morphology becomes progressively smoother and more volume-filling as density contrasts between successive shells are reduced. Our simulations identify extended shell-shock emission as a natural consequence of nested-shell evolution in recurrent novae. Remnant expansion regulates the slow fading of the soft component, and renewed ejecta-shell encounters drive hard-band variability on decade-long timescales. For a fiducial recurrent nova, the predicted diffuse soft X-ray luminosities are broadly consistent with the order of magnitude inferred for RS Oph, indicating that shock-heated gas can contribute appreciably to the observed X-ray environment.

astro-ph.HE↗

arXiv2026

Bipolar HII regions Produced by Cloud-Cloud Collisions

We use numerical experiments to explore two possibilities: (i) that Bipolar H II Regions are the result of Cloud-Cloud Collisions (CCCs), and (ii) that -- when allowance is made for the chaotic nature of such collisions, the short duration of the bipolar phase, and different viewing angles -- a large proportion of all H II Regions might be the aftermath of CCCs. To reduce the parameter space, our experiments only consider head-on collisions between two $500$ M$_\odot$ clouds, with three different levels of turbulence, and two different collision velocities; the collision velocities define the `collision axis'. In all experiments, OB stars only condense out after a Shock-Compressed Layer has formed (perpendicular to the collision axis), and fragmented to produce a Hub Filament System, with the OB stars forming in the Hub. Ionising radiation from the OB stars excites an H II Region, which tends to expand more rapidly in directions close to the collision axis, and more slowly in directions orthogonal to the collision axis, where it encounters the dense gas of the Shock-Compressed Layer. Consequently, the H II Region may appear bipolar, for a short period during its evolution, if observed at sufficiently large angle to the collision axis. Viewed from smaller angles, the waist appears as a Bright-Rim, similar to conventional approximately spherical H II Regions. Under this circumstance, there are other metrics -- based on the extent of diffuse freefree emission, the velocity dispersion of Radio Recombination Lines, dust emission at mid-infrared wavelengths -- that might indicate the aftermath of a CCC, and establish CCCs as a dominant trigger for high-mass star formation.

astro-ph.GA↗

arXiv2025

Feedback and Star Formation Efficiency in High-Mass Star-Forming Regions

To advance our understanding of massive star formation, it is essential to perform a comprehensive suite of simulations that explore the relevant parameter space and include enough physics to enable a comparison with observational data. We simulate the gravitational collapse of isolated, parsec-scale turbulent cores using the FLASH code, modelling stars as sink particles. Our simulations incorporate ionizing radiation and the associated radiation pressure from stellar sources, and non-ionizing radiation and its dust heating, along with self-consistent chemistry, to capture the properties of emerging ultra-compact HII regions. Dust, gas, and radiation temperature are computed independently. The initial conditions are informed by ALMAGAL observations. We assess stellar feedback, comparing ionizing radiation and radiation pressure. Ionizing radiation ultimately halts mass accretion on to sink particles, while direct radiation pressure enhances the expansion of HII regions. Heating from non-ionizing radiation suppresses fragmentation. We examine the effect of spatial resolution, finding that higher resolution leads to more sink particles which are situated in environments with higher densities. As a result, ionizing radiation remains trapped longer, allowing continued accretion and yielding a higher overall star formation efficiency (SFE). We explore the impact of varying initial conditions, including the core density profile, virial parameter, and metallicity. Our parameter study reveals that a flatter density profile, higher virial parameter, and increased metallicity promote fragmentation, potentially enhancing the SFE by slowing the growth of the most massive stars and delaying the onset of stellar feedback. Overall, we find SFEs between 35% and 57%. Stellar feedback dictates the final SFE.

astro-ph.GA↗

arXiv2025

SILCC -- IX. The multi-phase interstellar medium at low metallicity

The gas-phase metallicity affects heating and cooling processes in the star-forming galactic interstellar medium (ISM) as well as ionising luminosities, wind strengths, and lifetimes of massive stars. To investigate its impact, we conduct magnetohydrodynamic simulations of the ISM using the FLASH code as part of the SILCC project. The simulations assume a gas surface density of 10 M$_\odot$ pc$^{-2}$ and span metallicities from 1/50 Z$_\odot$ to 1 Z$_\odot$. We include non-equilibrium thermo-chemistry, a space- and time-variable far-UV background and cosmic ray ionisation rate, metal-dependent stellar tracks, the formation of HII regions, stellar winds, type II supernovae, and cosmic ray injection and transport. With the metallicity decreasing over the investigated range, the star formation rate decreases by more than a factor of ten, the mass fraction of cold gas decreases from 60% to 2.3%, while the volume filling fraction of the warm gas increases from 20% to 80%. Furthermore, the fraction of H$_\mathrm{2}$ in the densest regions drops by a factor of four, and the dense ISM fragments into approximately five times fewer structures at the lowest metallicity. Outflow mass loading factors remain largely unchanged, with values close to unity, except for a significant decline at the lowest metallicity. Including the major processes that regulate ISM properties, this study highlights the strong impact of gas phase metallicity on the star-forming ISM.

astro-ph.GA↗

arXiv2025

SILCC -- VIII: The impact of far-ultraviolet radiation on star formation and the interstellar medium

We present magnetohydrodynamic simulations of star formation in the multiphase interstellar medium to quantify the impact of non-ionising far-ultraviolet (FUV) radiation within the \textsc{Silcc Project} simulation framework. Our study incorporates the radiative transfer of ionising radiation and self-consistent modelling of variable FUV radiation from star clusters, advancing beyond previous studies using static or simplified FUV fields. This enables a more accurate capture of the dynamic interaction between radiation and the evolving ISM alongside other stellar feedback channels. The interstellar radiation field (ISRF) near young star clusters can reach $G_0 \approx 10^4$ (in Habing units), far exceeding the solar neighbourhood value of $G_0 = 1.7$. Despite these high intensities, FUV radiation minimally impacts the integrated star formation rate compared to ionising radiation, stellar winds, and supernovae. A slight reduction in star formation burstiness is linked to increased photoelectric (PE) heating efficiency by the variable FUV field. photoelectric (PE) heating efficiency by the variable FUV field. Dust near star-forming regions can be heated up to 60 K via the PE effect, with a broad temperature distribution. PE heating rates in variable FUV models exhibit higher peaks but lower averages than static ISRF models. Simulations under solar neighbourhood conditions without stellar winds or ionising radiation but with supernovae yield unexpectedly high star formation rates of $\sim 0.1 \mathrm{M_\odot~yr^{-1}~kpc^{-2}}$. Our analysis reveals increased cold neutral medium (CNM) volume-filling factors (VFF) outside stellar clusters, reduced thermally unstable gas, and sharper warm-cold gas separation. The variable FUV field also promotes a cold diffuse gas phase with a molecular component, exhibiting a VFF of $\sim5-10$~per cent.

astro-ph.GA↗

arXiv2025

The bright, dusty aftermath of giant eruptions & H-rich supernovae. Late interaction of supernova shocks & dusty circumstellar shells

The late-stage evolution of massive stars is marked by intense instability as they approach core-collapse. During these phases, giant stellar eruptions lead to exceptionally high mass-loss rates, forming significant amounts of dust. However, the survival of these dust grains is challenged by the powerful shock waves generated when the progenitor explodes as a supernova (SN). We explore the impact of hydrogen-rich SN explosions from 45, 50, and 60 M$_\odot$ progenitors on dust formed after these eruptions, focusing on interactions with circumstellar shells occurring from a few years to centuries after the event. Using 3D hydrodynamical simulations, we track the evolution of dust particles in a scenario that includes the progenitor's stellar wind, a giant eruption, and the subsequent SN explosion, following the mass budgets predicted by stellar evolution models. For a standard SN ejecta mass of 10 M$_\odot$ and kinetic energy of $10^{51}$ erg, only 25% of the dust mass survives 250 years post-explosion in a spherical circumstellar medium (CSM), while merely 2% remains a century after the explosion in a bipolar CSM. If the SN follows the eruption within a dozen years, 75% of the dust survives for a standard explosion, dropping to 20% for more massive ejecta (15-20 M$_\odot$) with kinetic energy of $5 \times 10^{51}$ erg. The geometry of the CSM and the early transition of the SN remnant into a radiative phase significantly influence dust survival. As the shock wave weakens and efficiently converts kinetic energy into thermal radiation (up to half of the injected kinetic energy) the likelihood of dust survival increases, affecting not only pre-existing dust in the CSM but also SN-condensed dust and ambient interstellar dust. Contrary to expectations, a larger fraction of the dust mass can survive if the SN occurs only a few years after the eruption.

astro-ph.SR↗

arXiv2025

Mass flows in the Galactic Center by supernovae of the circumnuclear disk

Context. The circumnuclear disk (CND) is presently the main supply of mass for the accretion onto the supermassive black hole (SMBH) in the Galactic Center (GC). While the accretion is relatively slow, it has been suspected that local episodic explosive events play an important role in the temporary mass inflow toward the SMBH, while also affecting the evolution of the CND. Aims. The aim of this study is to follow the changes in mass flows caused by supernova (SN) explosions nestled in or near the CND. Methods. We perform simulations with the grid-based MHD code FLASH of the inner 5 pc of the Milky Way GC, including gravitational potential, rotation, magnetic field, central wind source, and the warm gas of the CND, all mimicking the observed physical properties. Results. Assuming a M$_\mathrm{SN}=10$ M$_\odot$ as the mass of the precursor of the core-collapse SN event at various locations within 2 pc from the GC, we detect a temporary increase in the accretion rate, transferring an additional 2-60 M$_\odot$ of warm gas to the immediate vicinity of the SMBH, depending on the explosion site. At the same time, the kinetic energy of the SN blows away even mass from the CND; the additional warm gas leaving the simulation domain after the explosion is on the order of $\sim100$ M$_\odot$. In the studied cases, the impact on mass flows and the turbulence caused by the explosion cease after $\sim250$ kyr.

astro-ph.GA↗

arXiv2025

The impact of cosmic ray heating on the cooling of the low-metallicity interstellar medium

Low-metallicity environments are subject to inefficient cooling. They also have low dust-to-gas ratios and therefore less efficient photoelectric (PE) heating than in solar-neighbourhood conditions, where PE heating is one of the most important heating processes in the warm neutral interstellar medium (ISM). We perform magneto-hydrodynamic simulations of stratified ISM patches with a gas metallicity of 0.02 Z$_\odot$ as part of the SILCC project. The simulations include non-equilibrium chemistry, heating, and cooling of the low-temperature ISM as well as anisotropic cosmic ray (CR) transport, and stellar tracks. We include stellar feedback in the form of far-UV and ionising (FUV and EUV) radiation, massive star winds, supernovae, and CR injection. From the local CR energy density, we compute a CR heating rate that is variable in space and time. In this way, we can compare the relative impact of PE and CR heating on the metal-poor ISM and find that CR heating can dominate over PE heating. Models with a uniform CR ionisation rate suppress or severely delay star formation, since they provide a larger amount of energy to the ISM due to CR heating. Models with a variable CR ionisation rate form stars predominantly in pristine regions with low PE heating and CR ionisation rates where the metal-poor gas is able to cool efficiently. Because of the low metallicity, the amount of formed stars in all runs is not enough to trigger outflows of gas from the mid-plane.

astro-ph.GA↗

arXiv2024

Radiation transport methods in star formation simulations

Radiation transport plays a crucial role in star formation models, as certain questions within this field cannot be accurately addressed without taking it into account. Given the high complexity of the interstellar medium from which stars form, numerical simulations are frequently employed to model the star formation process. This study reviews recent methods for incorporating radiation transport into star formation simulations, discussing them in terms of the used algorithms, treatment of radiation frequency dependence, the interaction of radiation with the gas, and the parallelization of methods for deployment on supercomputers. Broadly, the algorithms fall into two categories: (i) moment-based methods, encompassing the flux-limited diffusion approximation, M1 closure, and variable Eddington tensor methods, and (ii) methods directly solving the radiation transport equation, including forward and reverse ray tracing, characteristics-based methods, and Monte Carlo techniques. Beyond discussing advantages and disadvantages of these methods, the review also lists recent radiation hydrodynamic codes implemented the described methods.

astro-ph.IM↗

arXiv2023

Tree-based solvers for adaptive mesh refinement code FLASH -- IV: An X-ray radiation scheme to couple discrete and diffuse X-ray emission sources to the thermochemistry of the interstellar medium

X-ray radiation, in particular radiation between 0.1 keV and 10 keV, is evident from both point-like sources, such as compact objects and T-Tauri young stellar objects, and extended emission from hot, cooling gas, such as in supernova remnants. The X-ray radiation is absorbed by nearby gas, providing a source of both heating and ionization. While protoplanetary chemistry models now often include X-ray emission from the central young stellar object, simulations of star-forming regions have yet to include X-ray emission coupled to the chemo-dynamical evolution of the gas. We present an extension of the {\sc TreeRay} reverse raytrace algorithm implemented in the {\sc Flash} magneto-hydrodynamic code which enables the inclusion of X-ray radiation from 0.1 keV $< E_γ <$ 100 keV, dubbed {\rm XrayTheSpot}. {\sc XrayTheSpot} allows for the use of an arbitrary number of bins, minimum and maximum energies, and both temperature-independent and temperature-dependent user-defined cross sections, along with the ability to include both point and extended diffuse emission and is coupled to the thermochemical evolution. We demonstrate the method with several multi-bin benchmarks testing the radiation transfer solution and coupling to the thermochemistry. Finally, we show two example star formation science cases for this module: X-ray emission from protostellar accretion irradiating an accretion disk and simulations of molecular clouds with active chemistry, radiation pressure, protostellar radiation feedback from infrared to X-ray radiation.

astro-ph.IM↗

arXiv2023

SILCC VII -- Gas kinematics and multiphase outflows of the simulated ISM at high gas surface densities

We present magnetohydrodynamic (MHD) simulations of the star-forming multiphase interstellar medium (ISM) in stratified galactic patches with gas surface densities $Σ_\mathrm{gas} =$ 10, 30, 50, and 100 $\mathrm{M_\odot\,pc^{-2}}$. The SILCC project simulation framework accounts for non-equilibrium thermal and chemical processes in the warm and cold ISM. The sink-based star formation and feedback model includes stellar winds, hydrogen-ionising UV radiation, core-collapse supernovae, and cosmic ray (CR) injection and diffusion. The simulations follow the observed relation between $Σ_\mathrm{gas}$ and the star formation rate surface density $Σ_\mathrm{SFR}$. CRs qualitatively change the outflow phase structure. Without CRs, the outflows transition from a two-phase (warm and hot at 1 kpc) to a single-phase (hot at 2 kpc) structure. With CRs, the outflow always has three phases (cold, warm, and hot), dominated in mass by the warm phase. The impact of CRs on mass loading decreases for higher $Σ_\mathrm{gas}$ and the mass loading factors of the CR-supported outflows are of order unity independent of $Σ_\mathrm{SFR}$. Similar to observations, vertical velocity dispersions of the warm ionised medium (WIM) and the cold neutral medium (CNM) correlate with the star formation rate as $σ_\mathrm{z} \propto Σ_\mathrm{SFR}^a$, with $a \sim 0.20$. In the absence of stellar feedback, we find no correlation. The velocity dispersion of the WIM is a factor $\sim 2.2$ higher than that of the CNM, in agreement with local observations. For $Σ_\mathrm{SFR} \gtrsim 1.5 \times 10^{-2}\,\mathrm{M}_\odot\,\mathrm{yr}^{-1}\,\mathrm{kpc}^{-2}$ the WIM motions become supersonic.

astro-ph.GA↗

arXiv2023

Simulations of pre-supernova feedback in spherical clouds

We present a one-dimensional radiation-hydrodynamic model of a spherically symmetric cloud evolving under the influence of the self-gravity and the feedback from a star cluster forming in its centre. On one hand, the model is simple due to its 1D geometry, on the other hand, the feedback includes the ionising radiation, stellar winds and the radiation pressure acting on gas and dust. The star cluster is formed from the gas flowing into the cloud centre and the feedback parameters are determined from stellar evolution models and the cluster star forming history. The model is compared to the semi-analytic code WARPFIELD implementing similar physical processes and exploring the scenario that the young cluster R136 in the Large Magellanic Cloud was formed due to re-collapse of the shell formed by the previous generation star cluster. A good qualitative agreement is found, however, $3 - 4$ times higher stellar mass is needed to disrupt the cloud in our model, because it takes into account (contrary to WARPFIELD) self-gravity of the cloud surrounding the shell. We use the model to explore star formation in clouds with different mass, radius and density profile measuring their star formation efficiency (SFE), i.e. the fraction of the cloud mass converted to stars. We found that SFE is a function of a single parameter, $\mathrm{log(SFE)} \propto -n_{hm}^{-0.46}$, with $n_{hm}$ being the cloud mean particle density within its half-mass radius. Furthermore, we found that the feedback efficiency, i.e. a fraction of the feedback energy retained by gas, has a nearly constant value $\sim 10^{-3}$.

astro-ph.GA↗

arXiv2022

Dust Grain Growth & Dusty Supernovae in Low-Metallicity Molecular Clouds

We present 3-D hydrodynamical models of the evolution of superbubbles powered by stellar winds and supernovae from young coeval massive star clusters within low metallicity ($Z = 0.02$Z$_{\odot}$), clumpy molecular clouds. We explore the initial stages of the superbubble evolution, including the occurrence of pair-instability and core-collapse supernovae. Our aim is to study the occurrence of dust grain growth within orbiting dusty clumps, and in the superbubble's swept-up supershell. We also aim to address the survival of dust grains produced by sequential supernovae. The model accounts for the star cluster gravitational potential and self-gravity of the parent cloud. It also considers radiative cooling (including that induced by dust) and a state-of-the-art population synthesis model for the coeval cluster. As shown before, a superbubble embedded into a clumpy medium becomes highly distorted, expanding mostly due to the hot gas streaming through low density channels. Our results indicate that in the case of massive ($\sim10^7$M$_{\odot}$) molecular clouds, hosting a super star cluster ($\sim5.6\times10^5$M$_{\odot}$), grain growth increments the dust mass at a rate $\sim4.8\times10^{-5}$M$_{\odot}$ yr$^{-1}$ during the first $2.5$Myr of the superbubble's evolution, while the net contribution of pair-instability and core-collapse supernovae to the superbubble's dust budget is $\sim1200$M$_{\odot} (M_{SC}/5.6\times10^{5}$M$_{\odot})$, where $M_{SC}$ is the stellar mass of the starburst. Therefore, dust grain growth and dust injection by supernovae lead to create, without invoking a top-heavy initial mass function, massive amounts of dust within low-metallicity star-forming molecular clouds, in accordance with the large dust mass present in galaxies soon after the onset of cosmic reionization.

astro-ph.GA↗

arXiv2022

X-ray emission from star cluster winds in starburst galaxies

Inspired by the excess soft X-ray emission recently detected in Green Pea galaxies, we model the soft X-ray emission (0.5 - 2.0 keV) of hot gas from star cluster winds. By combining individual star clusters, we estimate the soft X-ray emission expected from the typically unresolved diffuse hot gas in starburst galaxies, devoid of competing emission from e.g., AGN or other unresolved point sources. We use stellar models of sub-solar metallicities (0.02 $Z_{\odot}$ and 0.4 $Z_{\odot}$), and take into account supernova explosions for massive stars. For lower metallicities, we find that stellar winds do not contribute significantly ($\lesssim 3$ % of the mechanical energy) to the observed soft X-ray emission of normal star forming galaxies. For higher metallicities and possibly also for larger proportions of massive star clusters in the simulated starburst galaxies, we reproduce well the observed correlation between star formation rate and X-ray luminosity previously reported in the literature. However, we find that no combination of model assumptions is capable of reproducing the substantial soft X-ray emission observed from Green Pea galaxies, indicating that other emission mechanisms (i.e. unusually large quantities of High-/Low-Mass X-ray Binaries, Ultra-Luminous X-ray sources, a modified initial mass function, Intermediate-Mass Black Holes, or AGN) are more likely to be responsible for the X-ray excess.

astro-ph.GA↗

arXiv2021

Bonn Optimized Stellar Tracks (BoOST). Simulated Populations of Massive and Very Massive Stars for Astrophysical Applications

Massive and very massive stars can play important roles in stellar populations by ejecting strong stellar winds and exploding in energetic phenomena. It is therefore imperative that their behavior be properly accounted for in synthetic model populations. We present nine grids of stellar evolutionary model sequences, together with finely resolved interpolated sequences and synthetic populations, of stars with 9-500 Msun and with metallicities ranging from Galactic metallicity down to 1/250 Zsun. The stellar models were computed with the Bonn evolutionary code with consistent physical ingredients, and covering core hydrogen- and core helium-burning phases. The interpolation and population synthesis were performed with our newly developed routine 'synStars'. Eight of the grids represent slowly rotating massive stars with a normal or classical evolutionary path, while one grid represents fast-rotating, chemically homogeneously evolving models. The grids contain data on stellar wind properties such as estimated wind velocity and kinetic energy of the wind, as well as common stellar parameters such as mass, radius, surface temperature, luminosity, mass-loss rate, and surface abundances of 34 isotopes. We also provide estimates of the helium and carbon-oxygen core mass for calculating the mass of stellar remnants. The Bonn Optimized Stellar Tracks (BoOST) project is published as simple tables that include stellar models, interpolated tracks, and synthetic populations. Covering the broadest mass and metallicity range of any published massive star evolutionary model sets to date, BoOST is ideal for further scientific applications such as star formation studies in both low- and high-redshift galaxies.

astro-ph.SR↗

arXiv2021

Impact of the external radiation field on the structure and evolution of supernova remnants

We carry out 1D hydrodynamical simulations of the evolution of a spherically symmetric supernova remnant (SNR) subject to an external radiation field (ERF) that influences the cooling and heating rates of the gas. We consider homogeneous media with ambient hydrogen number densities $n_{\rm H,0}$ of $0.1$ and $1$ cm$^{-3}$ permeated by an average radiation field including the cosmic microwave, extragalactic, and Galactic backgrounds, attenuated by an effective column density $N_{\rm H,eff}$ from $10^{18}$ to $10^{21}$~cm$^{-2}$. Our results may be classified into two broad categories: at low $N_{\rm H,eff}$, the ERF presents little absorption in the ultraviolet (ionising) regime, and all the 'unshielded' cases feature an equilibrium temperature $T_{eq} \sim 7000$~K below which the ambient gas cannot cool further. In this scenario, the SNR develops a nearly isothermal shock profile whose shell becomes thicker over time. At higher $N_{\rm H,eff}$, the ERF is heavily absorbed in the UV range, yielding a roughly constant heating function for temperatures $\lesssim 10^4$ K. These `shielded' cases develop a thin, cold and dense shell throughout their evolution. Energy and momentum injection to the medium do not change significantly between both scenarios, albeit luminosity is higher and more uniformly distributed over the shell for unshielded SNR.

astro-ph.GA↗

arXiv2021

Tree-based solvers for adaptive mesh refinement code FLASH -- II: radiation transport module TreeRay

The treatment of radiative transfer with multiple radiation sources is a critical challenge in simulations of star formation and the interstellar medium. In this paper we present the novel TreeRay method for solving general radiative transfer problems, based on reverse ray tracing combined with tree-based accelerated integration. We implement TreeRay in the adaptive mesh refinement code FLASH, as a module of the tree solver developed by Wünsch et al. However, the method itself is independent of the host code and can be implemented in any grid based or particle based hydrodynamics code. A key advantage of TreeRay is that its computational cost is independent of the number of sources, making it suitable for simulations with many point sources (e.g. massive star clusters) as well as simulations where diffuse emission is important. A very efficient communication and tree-walk strategy enables TreeRay to achieve almost ideal parallel scalings. TreeRay can easily be extended with sub-modules to treat radiative transfer at different wavelengths and to implement related physical processes. Here, we focus on ionising (EUV) radiation and use the On-the-Spot approximation to test the method and its parameters. The ability to set the tree solver time step independently enables the speedy calculation of radiative transfer in a multi-phase interstellar medium, where the hydrodynamic time step is typically limited by the sound speed of the hot gas produced in stellar wind bubbles or supernova remnants. We show that complicated simulations of star clusters with feedback from multiple massive stars become feasible with TreeRay.

astro-ph.IM↗

arXiv2021

SILCC VI -- Multi-phase ISM structure, stellar clustering, and outflows with supernovae, stellar winds, ionising radiation and cosmic rays

We present simulations of the multi-phase interstellar medium (ISM) at solar neighbourhood conditions including thermal and non-thermal ISM processes, star cluster formation, and feedback from massive stars: stellar winds, hydrogen ionising radiation computed with the novel TreeRay radiative transfer method, supernovae (SN), and the injection of cosmic rays (CR). N-body dynamics is computed with a 4th-order Hermite integrator. We systematically investigate the impact of stellar feedback on the self-gravitating ISM with magnetic fields, CR advection and diffusion and non-equilibrium chemical evolution. SN-only feedback results in strongly clustered star formation with very high star cluster masses, a bi-modal distribution of the ambient SN densities, and low volume-filling factors (VFF) of warm gas, typically inconsistent with local conditions. Early radiative feedback prevents an initial starburst, reduces star cluster masses and outflow rates. Furthermore, star formation rate surface densities of $Σ_{\dot{M}_\star} = 1.4-5.9 \times 10^{-3}$ $\mathrm{M}_\odot\,\mathrm{yr}^{-1}\,\mathrm{kpc}^{-2}$, VFF$_\mathrm{warm} = 60-80$ per cent as well as thermal, kinetic, magnetic, and cosmic ray energy densities of the model including all feedback mechanisms agree well with observational constraints. On the short, 100 Myr, timescales investigated here, CRs only have a moderate impact on star formation and the multi-phase gas structure and result in cooler outflows, if present. Our models indicate that at low gas surface densities SN-only feedback only captures some characteristics of the star-forming ISM and outflows/inflows relevant for regulating star formation. Instead, star formation is regulated on star cluster scales by radiation and winds from massive stars in clusters, whose peak masses agree with solar neighbourhood estimates.

astro-ph.GA↗