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We employ the IllustrisTNG simulation data to investigate the turbulent and thermal motions of the cosmic baryonic fluid. With continuous wavelet transform techniques, we define the pressure spectra, or density-weighted velocity power spectra, as well as the spectral ratios, for both turbulent and thermal motions. We find that the magnitude of the turbulent pressure spectrum grows slightly from $z=4$ to $2$ and increases significantly from $z=2$ to $1$ at large scales, suggesting progressive turbulence injection into the cosmic fluid, whereas from $z=1$ to $0$, the spectrum remains nearly constant, indicating that turbulence may be balanced by energy transfer and dissipation. The magnitude of the turbulent pressure spectra also increases with environmental density, with the highest density regions showing a turbulent pressure up to six times that of thermal pressure. We also explore the dynamical effects of turbulence and thermal motions, discovering that while thermal pressure provides support against structure collapse, turbulent pressure almost counteracts this support, challenging the common belief that turbulent pressure supports gas against overcooling., Comment: 7 pages, 4 figures, 1 table, submitted to the MNRAS Letters. arXiv admin note: text overlap with arXiv:2404.11255

We study a planar bubble wall that is traveling at an ultrarelativistic speed through a thermal plasma. This situation may arise during a first-order electroweak phase transition in the early universe. As particles cross the wall, it is assumed that their mass grows from $m_a$ to $m_b$, and they are decelerated causing them to emit massless radiation ($m_c=0$). We are interested in the momentum transfer to the wall, the thermal pressure felt by the wall, and the resultant terminal velocity of the wall. We employ the semiclassical current radiation (SCR) formalism to perform these calculations. An incident-charged particle is treated as a point-like classical electromagnetic current, and the spectrum of quantum electromagnetic radiation (photons) is derived by calculating appropriate matrix elements. To understand how the spectrum depends on the thickness of the wall, we explore simplified models for the current corresponding to an abrupt and a gradual deceleration. For the model of abrupt deceleration, we find that the SCR formalism can reproduce the $P_\mathrm{therm} \propto \gamma_w^0$ scaling found in earlier work by assuming that the emission is soft, but if the emission is not soft the SCR formalism can be used to obtain $P_\mathrm{therm} \propto \gamma_w^2$ instead. For the model of gradual deceleration, we find that the wall thickness $L_w$ enters to cutoff the otherwise log-flat radiation spectrum above a momentum of $\sim \gamma_w^2 / L_w$, and we discuss the connections with classical electromagnetic bremsstrahlung., Comment: 29 pages plus appendices, 4 figures, 1 table. v2: clarifications added, matches JCAP version

We investigate the relationship between a galaxy cluster's hydrostatic equilibrium state, the entropy profile, $K$, of the intracluster gas, and the system's non-thermal pressure (NTP), within an analytic model of cluster structures. When NTP is neglected from the cluster's hydrostatic state, we find that the gas' logarithmic entropy slope, $k\equiv \mathrm{d}\ln K/\mathrm{d}\ln r$, converges at large halocentric radius, $r$, to a value that is systematically higher than the value $k\simeq1.1$ that is found in observations and simulations. By applying a constraint on these `pristine equilibrium' slopes, $k_\mathrm{eq}$, we are able to predict the required NTP that must be introduced into the hydrostatic state of the cluster. We solve for the fraction, $\mathcal{F}\equiv p_\mathrm{nt}/p$, of NTP, $p_\mathrm{nt}$, to total pressure, $p$, of the cluster, and we find $\mathcal{F}(r)$ to be an increasing function of halocentric radius, $r$, that can be parameterised by its value in the cluster's core, $\mathcal{F}_0$, with this prediction able to be fit to the functional form proposed in numerical simulations. The minimum NTP fraction, as the solution with zero NTP in the core, $\mathcal{F}_0=0$, we find to be in excellent agreement with the mean NTP predicted in non-radiative simulations, beyond halocentric radii of $r\gtrsim0.7r_{500}$, and in tension with observational constraints derived at similar radii. For this minimum NTP profile, we predict $\mathcal{F}\simeq0.20$ at $r_{500}$, and $\mathcal{F}\simeq0.34$ at $2r_{500}$; this amount of NTP leads to a hydrostatic bias of $b\simeq0.12$ in the cluster mass $M_{500}$ when measured within $r_{500}$. Our results suggest that the NTP of galaxy clusters contributes a significant amount to their hydrostatic state near the virial radius, and must be accounted for when estimating the cluster's halo mass using hydrostatic equilibrium approaches., Comment: 10 pages, 5 figures. Accepted for publication in PASA

In cosmological simulations of large-scale structure star formation and feedback in galaxies are modelled by so-called sub-grid models, that represent a physically motivated approximation of processes occurring below the resolution limit. However, when additional physical processes are considered in these simulations, for instance, magnetic fields or cosmic rays, they are often not consistently coupled within the descriptions of the underlying sub-grid star formation models. Here, we present a careful study on how one of the most commonly used sub-grid models for star formation in current large-scale cosmological simulations can be modified to self consistently include the effects of non-thermal components (e.g., magnetic fields) within the fluid. We demonstrate that our new modelling approach, that includes the magnetic pressure as an additional regulation on star formation, can reproduce global properties of the magnetic field within galaxies in a setup of an isolated Milky Way-like galaxy simulation, but is also successful in reproducing local properties such as the anti-correlation between the local magnetic field strength with the local star formation rate as observed in galaxies (i.e. NGC 1097). This reveals how crucial a consistent treatment of different physical processes is within cosmological simulations and gives guidance for future simulations., Comment: 15 pages, 14 figures, comments welcome. Submitted to MNRAS

Solar partially ionized plasma is frequently modeled using single-fluid (1F) or two-fluid (2F) approaches. In the 1F case, charge-neutral interactions are often described through ambipolar diffusion, while the 2F model fully considers charge-neutral drifts. Here, we expand the definition of the ambipolar diffusion coefficient to include inelastic collisions (ion/rec) in two cases: a VAL3C 1D model and a 2F simulations of the Rayleigh-Taylor instability (RTI) in a solar prominence thread based on \cite{PopLukKho2021aa, PopLukKho2021ab}. On one side, we evaluate the relative importance of the inelastic contribution, compared to elastic and charge-exchange collisions. On the other side, we compare the contributions of ion/rec, thermal pressure, viscosity, and magnetic forces to the charge-neutral drift velocity of the turbulent flow of the RTI. Our analysis reveals that the contribution of inelastic collisions to the ambipolar diffusion coefficient is negligible across the chromosphere, allowing the classical definition of this coefficient to be safely used in 1F modeling. However, in the transition region, the contribution of inelastic collisions can become as significant as that of elastic collisions. Furthermore, we ascertain that the thermal pressure force predominantly influences the charge-neutral drifts in the RTI model, surpassing the impact of the magnetic force., Comment: Accepted

We present a modelization of the non-thermal pressure, $P_{NT}$, and we apply it to the X-ray (and Sunayev-Zel'dovich) derived radial profiles of the X-COP galaxy clusters. We relate the amount of non-thermal pressure support to the hydrostatic bias, $b$, and speculate on how we can interpret this $P_{NT}$ in terms of the expected levels of turbulent velocity and magnetic fields. Current upper limits on the turbulent velocity in the intracluster plasma are used to build a distribution $\mathcal{N}(

To experimentally search for signals of the Gardner transition, an active quasi-thermal granular glass is constructed using a monolayer of air-fluidized star-shaped granular particles. The pressure of the system is controlled by adjusting the tension exerted on an enclosing boundary. Velocity distributions of the internal particles and the scaling of the pressure, density, effective-temperature, and relaxation time are examined, demonstrating that the system has important features of a thermal system. Using a pressure-based quenching protocol that brings the system into deeper glassy states, signals of the Gardner transition are detected via cage size and separation order parameters for both particle positions and orientations, offering experimental evidence of the Gardner transition for a system with in low spatial dimensions that is quasi-thermal., Comment: 5 pages, 4 figures

Modeling collisionless magnetic reconnection rate is an outstanding challenge in basic plasma physics research. While the seemingly universal rate of an order $\mathcal{O}(0.1)$ is often reported in the low-$\beta$ regime, it is not clear how reconnection rate scales with a higher plasma $\beta$. Due to the complexity of the pressure tensor, the available reconnection rate model is limited to the low plasma-$\beta$ regime, where the thermal pressure is arguably negligible. However, the thermal pressure effect becomes important when $\beta \gtrsim \mathcal{O}(1)$. Using first-principle kinetic simulations, we show that both the reconnection rate and outflow speed drop as $\beta$ gets larger. A simple analytical framework is derived to take account of the self-generated pressure anisotropy and pressure gradient in the force-balance around the diffusion region, explaining the varying trend of key quantities and reconnection rates in these simulations with different $\beta$. The predicted scaling of the normalized reconnection rate is $\simeq \mathcal{O}(0.1/\sqrt{\beta_{i0}})$ in the high $\beta$ limit, where $\beta_{i0}$ is the ion $\beta$ of the inflow plasma., Comment: 19 pages, 7 figures, accepted for publication in ApJ

We use a set of 45 simulated clusters with a wide mass range ($8\times 10^{13} < M_{500}~[$M$_{\odot}]~< 2\times 10^{15}$) to investigate the effect of varying hydrodynamics flavours on cluster mass estimates. The cluster zooms were simulated using the same cosmological models as the BAHAMAS and C-EAGLE projects, leading to differences in both the hydrodynamic solvers and the subgrid physics but still producing clusters which broadly match observations. At the same mass resolution as BAHAMAS, for the most massive clusters ($M_{500} > 10^{15}$ M$_{\odot}$), we find changes in the SPH method produce the greatest differences in the final halo, while the subgrid models dominate at lower mass. By calculating the mass of all of the clusters using different permutations of the pressure, temperature and density profiles, created with either the true simulated data or mock spectroscopic data, we find that the spectroscopic temperature causes a bias in the hydrostatic mass estimates which increases with the mass of the cluster, regardless of the SPH flavour used. For the most massive clusters, the estimated mass of the cluster using spectroscopic density and temperature profiles is found to be as low as 50 per cent of the true mass compared to $\sim$ 90 per cent for low mass clusters. When including a correction for non-thermal pressure, the spectroscopic hydrostatic mass estimates are less biased on average and the mass dependence of the bias is reduced, although the scatter in the measurements does increase., Comment: 21 pages, 14 figures. Accepted for publication by MNRAS

We explore the relation between the star formation rate surface density ($\Sigma$SFR) and the interstellar gas pressure for nearby compact starburst galaxies. The sample consists of 17 green peas and 19 Lyman break analogs. Green peas are nearby analogs of Ly$\alpha$ emitters at high redshift and Lyman break analogs are nearby analogs of Lyman break galaxies at high redshift. We measure the sizes for green peas using Hubble Space Telescope Cosmic Origins Spectrograph (COS) NUV images with a spatial resolution of $\sim$ 0.05$^{''}$. We estimate the gas thermal pressure in HII regions by $P = N_{total}Tk{_B} \simeq 2n_{e}Tk{_B}$. The electron density is derived using the [SII] doublet at 6716,6731 \AA, and the temperature is calculated from the [OIII] lines. The correlation is characterized by $\Sigma$ SFR = 2.40$\times$10$^{-3\,}$M$_{\odot\,}$yr$^{-1\,}$kpc$^{-2}$$\left(\frac{P/k_{B}}{10^{4}cm^{-3}K}\right)^{1.33}$. Green peas and Lyman break analogs have high $\Sigma$SFR up to 1.2 M$_{\odot\,}$yr$^{-1\,}$kpc$^{-2}$ and high thermal pressure in HII region up to P/k$_B$ $\sim$10$^{7.2}{\rm\, K\, cm}^{-3}$. These values are at the highest end of the range seen in nearby starburst galaxies. The high gas pressure and the correlation, are in agreement with those found in star-forming galaxies at z $\sim$ 2.5. These extreme pressures are shown to be responsible for driving galactic winds in nearby starbursts. These outflows may be a crucial in enabling Lyman-$\alpha$ and Lyman-continuum to escape., Comment: 16 pages, 6 figures, 1 table; Accepted for publication in ApJ

Galaxy clusters are the endpoints of structure formation and are continuously growing through the merging and accretion of smaller structures. Numerical simulations predict that a fraction of their energy content is not yet thermalized, mainly in the form of kinetic motions (turbulence, bulk motions). Measuring the level of non-thermal pressure support is necessary to understand the processes leading to the virialization of the gas within the potential well of the main halo and to calibrate the biases in hydrostatic mass estimates. We present high-quality measurements of hydrostatic masses and intracluster gas fraction out to the virial radius for a sample of 12 nearby clusters with available XMM-Newton and Planck data. We compare our hydrostatic gas fractions with the expected universal gas fraction to constrain the level of non-thermal pressure support. We find that hydrostatic masses require little correction and infer a median non-thermal pressure fraction of $\sim6\%$ and $\sim10\%$ at $R_{500}$ and $R_{200}$, respectively. Our values are lower than the expectations of hydrodynamical simulations, possibly implying a faster thermalization of the gas. If instead we use the mass calibration adopted by the Planck team, we find that the gas fraction of massive local systems implies a mass bias $1-b=0.85\pm0.05$ for SZ-derived masses, with some evidence for a mass-dependent bias. Conversely, the high bias required to match Planck CMB and cluster count cosmology is excluded by the data at high significance, unless the most massive halos are missing a substantial fraction of their baryons., Comment: 11 pages, 7 figures, A&A in press. This is one of three companion papers (including Ghirardini et al. and Ettori et al.) on the X-COP sample. X-COP data products are available for download on https://www.astro.unige.ch/xcop

Recently a filamentation instability was observed when a laser-generated pair cloud interacted with an ambient plasma. The magnetic field it drove was strong enough to magnetize and accelerate the ambient electrons. It is of interest to determine if and how pair cloud-driven instabilities can accelerate ions in the laboratory or in astrophysical plasma. For this purpose, the expansion of a localized pair cloud with the temperature 400 keV into a cooler ambient electron-proton plasma is studied by means of one-dimensional particle-in-cell (PIC) simulations. The cloud's expansion triggers the formation of electron phase space holes that accelerate some protons to MeV energies. Forthcoming lasers might provide the energy needed to create a cloud that can accelerate protons., Comment: 5 pages 4 figures, accepted for publication in Physics of Plasmas

Dynamic and thermal processes regulate the structure of the multi-phase interstellar medium (ISM), and ultimately establish how galaxies evolve through star formation. Thus, to constrain ISM models and better understand the interplay of these processes, it is of great interest to measure the thermal pressure ($P_{\rm th}$) of the diffuse, neutral gas. By combining [C II] 158 $\mu$m, HI, and CO data from 31 galaxies selected from the Herschel KINGFISH sample, we have measured thermal pressures in 534 predominantly atomic regions with typical sizes of $\sim$1 kiloparsec. We find a distribution of thermal pressures in the $P_{\rm th}/k\sim10^3-10^5$ K cm$^{-3}$ range. For a sub-sample of regions with conditions similar to those of the diffuse, neutral gas in the Galactic plane, we find thermal pressures that follow a log-normal distribution with a median value of $P_{\rm th}/k\approx3600$ K cm$^{-3}$. These results are consistent with thermal pressure measurements using other observational methods. We find that $P_{\rm th}$ increases with radiation field strength and star formation activity, as expected from the close link between the heating of the gas and the star formation rate. Our thermal pressure measurements fall in the regime where a two-phase ISM with cold and warm neutral medium could exist in pressure equilibrium. Finally, we find that the midplane thermal pressure of the diffuse gas is about $\sim30$% of the vertical weight of the overlying ISM, consistent with results from hydrodynamical simulations of self-regulated star formation in galactic disks., Comment: Accepted for publication in ApJ on Dec. 20th, 2016; 17 pages; 7 figures and 1 table

UV absorption studies with FUSE have observed H2 molecular gas in translucent and diffuse clouds. Observations of the 158 micron [C II] fine structure line with Herschel also trace the same H2 molecular gas in emission. We present [C II] observations along 27 lines of sight (LOSs) towards target stars of which 25 have FUSE H2 UV absorption. We detect [C II] emission features in all but one target LOS. For three Target LOSs, which are close to the Galactic plane, we also present position-velocity maps of [C II] emission observed by HIFI in on-the-fly spectral line mapping. We use the velocity resolved [C II] spectra towards the target LOSs observed by FUSE to identify C II] velocity components associated with the H2 clouds. We analyze the observed velocity integrated [C II] spectral line intensities in terms of the densities and thermal pressures in the H2 gas using the H2 column densities and temperatures measured by the UV absorption data. We present the H2 gas densities and thermal pressures for 26 target LOSs and from the [C II] intensities derive a mean thermal pressure in the range 6100 to 7700 K cm^-3 in diffuse H2 clouds. We discuss the thermal pressures and densities towards 14 targets, comparing them to results obtained using the UV absorption data for two other tracers CI and CO., Comment: 16 pages; 13 figures

Galaxy cluster mass determinations achieved using X-ray and Sunyaev-Zel'dovich data combined with the assumption of hydrostatic equilibrium are generally biased. The bias exists for two main reasons: non-thermal pressure forces are expected to contribute to the overall pressure balance and deviations from spherical symmetry and hydrostatic equilibrium can be present. In this paper, we use a sample of zoom-in hydrodynamical simulations of galaxy clusters to measure the magnitude of hydrostatic bias and the non-thermal contribution to the total pressure. We propose a new empirical model for non-thermal pressure based on our simulations that can be applied to observations. We show that our model can be successfully applied to remove most of the bias related to neglection of non-thermal pressure, which is usually not included in hydrostatic cluster mass profile reconstructions. The use of this model may significantly improve the calibration of cluster scaling relations that are a key tool for cluster cosmology., Comment: 10 pages, 7 figures, 2 tables, submitted to MNRAS

We present a numerical solver for plasma dynamics simulations in Hall magnetohydrodynamic (HMHD) approximation in one, two and three dimensions. We consider both isotropic and anisotropic thermal pressure cases, where a general gyrotropic approximation is used. Both explicit energy conservation equation and general polytropic state equations are considered. The numerical scheme incorporates second-order Runge-Kutta advancing in time and Kurganov-Tadmor scheme with van Leer flux limiter for the approximation of fluxes. A flux-interpolated constrained-transport approach is used to preserve solenoidal magnetic field in the simulations. The implemented code is validated using several test problems previously described in the literature. Additionally, we propose a new validation method for HMHD codes based on solitary waves that provides a possibility of quantitative rigorous testing in nonlinear (large amplitude) regime as an extension to standard tests using small-amplitude whistler waves. Quantitative tests of accuracy and performance of the implemented code show the fidelity of the proposed approach., Comment: Accepted for publication in Journal of Computational Physics, 20 pages, 15 figures

Non-thermal pressure in galaxy clusters leads to underestimation of the mass of galaxy clusters based on hydrostatic equilibrium with thermal gas pressure. This occurs even for dynamically relaxed clusters that are used for calibrating the mass-observable scaling relations. We show that the analytical model for non-thermal pressure developed in Shi & Komatsu 2014 can correct for this so-called 'hydrostatic mass bias', if most of the non-thermal pressure comes from bulk and turbulent motions of gas in the intracluster medium. Our correction works for the sample average irrespective of the mass estimation method, or the dynamical state of the clusters. This makes it possible to correct for the bias in the hydrostatic mass estimates from X-ray surface brightness and the Sunyaev-Zel'dovich observations that will be available for clusters in a wide range of redshifts and dynamical states., Comment: 9 pages, 8 figures, published in MNRAS