Radiative transfer of ionizing radiation through gas and dust: stellar source case

We present a new dust extension to the Monte Carlo radiative transfer code crash, which enables it to simulate the propagation of ionizing radiation through mixtures of gas and dust. The new code is applied to study the impact of dust absorption on idealized galactic H II regions and on small scale reionization. We find that H II regions are reduced in size by the presence of dust, while their inner temperature and ionization structure remain largely unaffected. In the small scale reionization simulation, dust hardens ionization fronts and delays the overlap of ionized bubbles. This effect is found to depend only weakly on the assumed abundance of dust in underdense regions.Comment: 17 pages, 14 figures. Accepted for publication in MNRA

Thermodynamic modeling for numerical simulations based on the generalized cubic equation of state

We further elaborate on the generalized formulation for cubic equation of state proposed by Cismondi and Mollerup [Fluid Phase Equilib. 232 (2005)]. With this formulation all well-known cubic equations of state can be described with a certain pair of values, which allows for a generic implementation of different equations of state. Based on this generalized formulation, we derive a complete thermodynamic model for computational fluid dynamics (CFD) simulations by providing the resulting correlations for all required thermodynamic properties. For the transport properties, we employ the Chung correlations. Our generic implementation includes the often used equations of state Soave-Redlich-Kwong and Peng-Robinson and the Redlich-Kwong-Peng-Robinson (RKPR) equation of state. The first two assume a universal compressibility factor and are therefore only suitable for fluids with a matching critical compressibility. The Redlich-Kwong-Peng-Robinson overcomes this limitation by considering the equation of state parameter as function of the critical compressibility. We compare the resulting thermodynamic modeling for the three equations of state for selected fluids with each other and CoolProp reference data. As supplementary material to this paper, we provide a Python tool called real gas thermodynamic python library (realtpl). This tool can be used to evaluate and compare the results for a wide range of different fluids. Additionally, we also provide the implementation of the generalized form in OpenFOAM

Ionizing photon production and escape fractions during cosmic reionization in the TNG50 simulation

In this work we investigate the dependence of the escape fraction of ionizing photons, $f_{\rm esc}$, on various galaxy and host halo properties during the epoch of reionization. We post-process the TNG50 magneto-hydrodynamical simulation from the IllustrisTNG project using the 3D multi-frequency radiative transfer code CRASH. Our work covers the stellar mass range $10^6 \lesssim M_\star/{\rm M_\odot} \lesssim 10^8$ at redshifts $6 < z < 10$. Adopting an unresolved, cloud-scale escape fraction parameter of unity, the halo escape fraction $f_{\rm esc}$ increases with mass from $\sim 0.3$ at $M_\star = 10^6$M$_\odot$ to $\sim 0.6$ at $M_\star = 10^{7.5}$M$_\odot$, after which we find hints of a turnover and decreasing escape fractions for even more massive galaxies. However, we demonstrate a strong and non-linear dependence of $f_{\rm esc}$ on the adopted sub-grid escape fraction. In addition, $f_{\rm esc}$ has significant scatter at fixed mass, driven by diversity in the ionizing photon rate together with a complex relationship between (stellar) source positions and the underling density distribution. The global emissivity is consistent with observations for reasonable cloud-scale absorption values, and halos with a stellar mass $\lesssim 10^{7.5}$M$_\odot$ contribute the majority of ionizing photons at all redshifts. Incorporating dust reduces $f_{\rm esc}$ by a few percent at $M_\star \lesssim 10^{6.5}$M$_\odot$, and up to 10\% for larger halos. Our multi-frequency approach shows that $f_{\rm esc}$ depends on photon energy, and is reduced substantially at $E>54.4$eV versus lower energies. This suggests that the impact of high energy photons from binary stars is reduced when accounting for an energy dependent escape fraction.Comment: 19 pages, 15 figures, submitted to MNRA

X­-rays ionization and heating by high­ redshift quasars

Here we discuss the impact of quasars (QSOs) on the ionization and heating of host and field galaxies and on the intergalactic medium (IGM), by showing the results of radiative transfer simulations accounting for X­rays and secondary electrons. By adopting a multi­scale approach (100 h­1 / 25 h­1 / 1 h­1 cMpc boxes) we study the importance of feedback in different environments and the impact on observables present at different scales. The role of QSO in the general context of a full reionization simulation [1­2] and their relative contribution in the evolution of the first Gyr of our Universe is addressed in the first box. The second box considers a single QSO HII region in a case matching a ULAS J1120+0641­like QSO. Implications for the HII region properties are also discussed [3]. Finally, new small scale simulations accounting for X­rays triggered photo­dissociation regions and metal ions are introduced in the last box [5­6­7]

The Role of Dust in the Transfer of Ionizing Radiation

Dust has been recognized as a crucial component of galaxies that strongly influences Interstellar Medium (ISM) chemistry and physics, such as the transport of electromagnetic radiation. In particular sources of hydrogen ionizing radiation (hν ≥ 13.6 eV) are frequently associated with dusty environments, resulting in a complicated interplay of radiation, gas and dust. By extension dust also shapes the spectra of radiation that escapes galaxies and thus might have played an indirect role in cosmic reionization. To quantitatively study these processes we extend the radiative transfer code CRASH by a dust module. While at the moment only the absorption of radiation is modelled, we are working on refining the treatment of the complex physics of solid grains to include effects such as grain charging and heating. To test the current implementation we perform simulations in different astrophysical environments using a Milky Way dust model from the literature. We confirm that the results are in accordance with expectations from more qualitative considerations

Radiative transfer of ionizing radiation through gas and dust: stellar source case

We present a new dust extension to the Monte Carlo radiative transfer code CRASH, which enables it to simulate the propagation of ionizing radiation through mixtures of gas and dust. The new code is applied to study the impact of dust absorption on idealized galactic H II regions and on small scale reionization. In general agreement with semianalytic predictions we find that H II regions are reduced in size by the presence of dust, while their inner temperature and ionization structure remain largely unaffected. In the small scale reionization simulation, dust hardens ionization fronts and delays the overlap of ionized bubbles. This effect is found to depend only weakly on the assumed abundance of dust in underdense regions. Grain charging is presented as a preview of future extensions focussing on the photo-electrons released by dust

Galactic extinction within 400pc in cartesian coordinates

Galactic 3D extinction of Leike et al 2020 using data of Anders et al 2019. See readme.txt or the information within the h5 files for more details