Numerical simulations of shocks encountering clumpy regions

Alūzas, R.; Pittard, J. M.; Hartquist, T. W.; Falle, S. A. E. G.; Langton, Rebecca

doi:10.1111/j.1365-2966.2012.21598.x

Cited by 31 publications

(30 citation statements)

References 48 publications

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“…Thus, models Uni-0-0 and Tur-0-0 produce filaments that are structurally different: a uniform cloud favours the formation of a filament with a single current sheet while a turbulent cloud produces a filamentary tail filled with several highly-magnetised knots and sub-filaments (at which E m,cloud /E m 0 ∼ 10 2 −10 3 ). Similar structures have been found in purely HD and MHD simulations of shocks interacting with inhomogeneous media, i.e., systems that have more than one cloud (e.g., see Poludnenko et al 2002;Pittard et al 2005;Raga et al 2009;Alūzas et al 2012Alūzas et al , 2014Rybakin, Smirnov & Goryachev 2016).…”

Section: On the Morphology Of Filamentssupporting

confidence: 70%

Filament formation in wind–cloud interactions– II. Clouds with turbulent density, velocity, and magnetic fields

Banda-Barragán

Federrath

Crocker

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present a set of numerical experiments designed to systematically investigate how turbulence and magnetic fields influence the morphology, energetics, and dynamics of filaments produced in wind-cloud interactions. We cover three-dimensional, magnetohydrodynamic systems of supersonic winds impacting clouds with turbulent density, velocity, and magnetic fields. We find that log-normal density distributions aid shock propagation through clouds, increasing their velocity dispersion and producing filaments with expanded cross sections and highly-magnetised knots and sub-filaments. In self-consistently turbulent scenarios the ratio of filament to initial cloud magnetic energy densities is ∼ 1. The effect of Gaussian velocity fields is bound to the turbulence Mach number: Supersonic velocities trigger a rapid cloud expansion; subsonic velocities only have a minor impact. The role of turbulent magnetic fields depends on their tension and is similar to the effect of radiative losses: the stronger the magnetic field or the softer the gas equation of state, the greater the magnetic shielding at wind-filament interfaces and the suppression of Kelvin-Helmholtz instabilities. Overall, we show that including turbulence and magnetic fields is crucial to understanding cold gas entrainment in multi-phase winds. While cloud porosity and supersonic turbulence enhance the acceleration of clouds, magnetic shielding protects them from ablation and causes Rayleigh-Taylor-driven sub-filamentation. Wind-swept clouds in turbulent models reach distances ∼ 15 − 20 times their core radius and acquire bulk speeds ∼ 0.3 − 0.4 of the wind speed in one cloud-crushing time, which are three times larger than in non-turbulent models. In all simulations the ratio of turbulent magnetic to kinetic energy densities asymptotes at ∼ 0.1 − 0.4, and convergence of all relevant dynamical properties requires at least 64 cells per cloud radius.

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Section: On the Morphology Of Filamentssupporting

confidence: 70%

Filament formation in wind–cloud interactions– II. Clouds with turbulent density, velocity, and magnetic fields

Banda-Barragán

Federrath

Crocker

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…For instance, an alternative explanation for the observed differences could be that the mass in the compressive model (in this particular sample case) is arranged in such a way that high-density gas is somewhat protected from the wind by upstream gas that prevents it from being ablated, thus delaying its disruption. This would be akin to the shielding processes reported by Alūzas et al 2014;Forbes & Lin 2018 for multi-cloud media and cold gas streams embedded in hot outflows (although the mixing of upstream gas can enhance the turbulence-driven destruction of downstream clouds in some multi-cloud configurations; see e.g., Poludnenko, Frank & Blackman 2002;Alūzas et al 2012). However, as we show below, the differences seen in 3D solenoidal and compressive cloud models can actually be linked to the initial standard deviation of their density PDFs.…”

Section: Solenoidal Versus Compressive Cloud Modelsmentioning

confidence: 76%

“…All the diagnostics presented in Figure 6 show similar trends and solenoidal-to-compressive ratios. However, mixing processes are more effective in 3D models owing to their spherical geometry, to the extra degree of freedom intrinsic to this configuration (see also Xu & Stone 1995;Alūzas et al 2012;Sparre et al 2018), and to the softer standard deviations of the initial 3D density PDFs that we set up for these models. This is in agreement with previous studies, which show that 3D spherical clouds are more accelerated and mixed than their 2D and 3D cylindrical counterparts (e.g., see Sparre et al 2018), while 2.5D and 3D spherical clouds evolve similarly until non-azimuthal instabilities start to grow in 3D simulations (e.g., see Pittard & Parkin 2016).…”

Section: Gas Mixing and Dispersionmentioning

confidence: 99%

On the dynamics and survival of fractal clouds in galactic winds

Banda-Barragán

Zertuche

Federrath

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Recent observations suggest that dense gas clouds can survive even in hot galactic winds. Here we show that the inclusion of turbulent densities with different statistical properties has significant effects on the evolution of wind-swept clouds. We investigate how the initial standard deviation of the log-normal density field influences the dynamics of quasi-isothermal clouds embedded in supersonic winds. We compare uniform, fractal solenoidal, and fractal compressive cloud models in both 3D and 2D hydrodynamical simulations. We find that the processes of cloud disruption and dense gas entrainment are functions of the initial density distribution in the cloud. Fractal clouds accelerate, mix, and are disrupted earlier than uniform clouds. Within the fractal cloud sample, compressive clouds retain high-density nuclei, so they are more confined, less accelerated, and have lower velocity dispersions than their solenoidal counterparts. Compressive clouds are also less prone to Kelvin-Helmholtz and Rayleigh-Taylor instabilities, so they survive longer than solenoidal clouds. By comparing the cloud properties at the destruction time, we find that dense gas entrainment is more effective in uniform clouds than in either of the fractal clouds, and it is more effective in solenoidal than in compressive models. In contrast, mass loading into the wind is more efficient in compressive cloud models than in uniform or solenoidal models. Overall, wide density distributions lead to inefficient entrainment, but they facilitate mass loading and favour the survival of very dense gas in hot galactic winds.

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“…Prochter et al ). Thus, if the gas probed by this absorption system is poorly mixed, it is plausible that the gas is entrained in an outflowing wind (see Schaye, Carswell & Kim ; Alūzas et al ). However, the current observational evidence suggests that Mg ii entrained in outflowing material may, on average, have a maximum projected extension of ∼50 kpc.…”

Section: Discussionmentioning

confidence: 99%

Discovery of multiphase cold accretion in a massive galaxy at z = 0.7

Kacprzak

Churchill

Steidel

et al. 2012

Monthly Notices of the Royal Astronomical Society

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We present detailed photo+collisional ionization models and kinematic models of the multiphase absorbing gas, detected within the Hubble Space Telescope(HST)/COS, HST/STIS and Keck/HIRES spectra of the background quasar TON 153 at 104 kpc along the projected minor axis of a star-forming spiral galaxy (z = 0.6610). Complementary g r i Ks photometry and stellar population models indicate that the host galaxy is dominated by an ∼4 Gyr stellar population with slightly greater than solar metallicity and has an estimated log M * = 11 and a log M vir = 13. Photoionization models of the low-ionization absorption (Mg I, Si II, Mg II and C III), which trace the bulk of hydrogen, constrain the multicomponent gas to be cold (log T = 3.8-5.2) and metal poor (−2.6 ≤ [X/H] ≤ 1.32). A lagging halo model reproduces the low-ionization absorption kinematics, suggesting gas coupled to the disc angular momentum, consistent with cold accretion mode material in simulations. The C IV and O VI absorption is best modelled in a separate collisionally ionized metal-poor (−2.50 ≤ [X/H] ≤ −1.93) warm phase with log T = 5.3. Although their kinematics are consistent with a wind model, given the 2-2.5 dex difference between the galaxy stellar metallicity and the absorption metallicity we indicate that the gas cannot arise from galactic winds. We discuss and conclude that although the quasar sightline passes along the galaxy minor axis at a projected distance of 0.3 virial radii, well inside its virial shock radius, the combination of the relative kinematics, temperatures and relative metallicities indicates that the multiphase absorbing gas arises from cold accretion around this massive galaxy. Our results appear to contradict recent interpretations that absorption probing the projected minor axis of a galaxy is sampling winds.

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Numerical simulations of shocks encountering clumpy regions

Cited by 31 publications

References 48 publications

Filament formation in wind–cloud interactions– II. Clouds with turbulent density, velocity, and magnetic fields

Filament formation in wind–cloud interactions– II. Clouds with turbulent density, velocity, and magnetic fields

On the dynamics and survival of fractal clouds in galactic winds

Discovery of multiphase cold accretion in a massive galaxy at z = 0.7

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