Magnetized High Velocity Clouds in the Galactic Halo: A New Distance Constraint

Grønnow, Asger; Tepper-García, Thor; Bland-Hawthorn, Joss; McClure-Griffiths, N. M.

doi:10.3847/1538-4357/aa7ed2

Cited by 33 publications

(36 citation statements)

References 66 publications

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“…This asymmetry is similar to that observed in previous studies (i.e. Gregori et al 1999;McCourt et al 2015;Grønnow et al 2017).…”

Section: Influence Of Transverse Fieldssupporting

confidence: 93%

“…The transverse fields produce a smooth, laminar flow with reduced effects of Kelvin-Helmhotlz (KH) instabilities due to the reorienting of the field lines as the wind pulls the lines to be more aligned with the flow. This is similar to what has been observed in previous studies (Orlando et al 2008;Banda-Barragán et al 2016;Grønnow et al 2017Grønnow et al , 2018. In the right panels of material is surrounded by an envelope of gas with β ≈ 1.…”

Section: Influence Of Transverse Fieldssupporting

confidence: 90%

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The Launching of Cold Clouds by Galaxy Outflows. III. The Influence of Magnetic Fields

Cottle

Scannapieco

Brüggen

et al. 2020

ApJ

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Motivated by observations of outflowing galaxies, we investigate the combined impact of magnetic fields and radiative cooling on the evolution of cold clouds embedded in a hot wind. We perform a collection of three-dimensional adaptive mesh refinement, magnetohydrodynamical simulations that span two resolutions, and include fields that are aligned and transverse to the oncoming, super-Alfvénic material. Aligned fields have little impact on the overall lifetime of the clouds over the non-magnetized case, although they do increase the mixing between the wind and cloud material by a factor of ≈ 3. Transverse fields lead to magnetic draping, which isolates the clouds, but they also squeeze material in the direction perpendicular to the field lines, which leads to rapid mass loss. A resolution study suggests that the magnetized simulations have somewhat better convergence properties than nonmagnetized simulations, and that a resolution of 64 zones per cloud radius is sufficient to accurately describe these interactions. We conclude that the combined effects of radiative cooling and magnetic fields are dependent on field orientation, but are unlikely to enhance cloud lifetimes beyond the effect of radiative cooling alone.

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“…This asymmetry is similar to that observed in previous studies (i.e. Gregori et al 1999;McCourt et al 2015;Grønnow et al 2017).…”

Section: Influence Of Transverse Fieldssupporting

confidence: 93%

Section: Influence Of Transverse Fieldssupporting

confidence: 90%

The Launching of Cold Clouds by Galaxy Outflows. III. The Influence of Magnetic Fields

Cottle

Scannapieco

Brüggen

et al. 2020

ApJ

View full text Add to dashboard Cite

show abstract

“…Magnetic fields have also been shown to delay cloud destruction by stabilising wind-cloud shear layers (Mac Low et al 1994;Shin et al 2008;Grønnow et al 2017;Banda-Barragán et al 2016Grønnow et al 2018) and favour RT-induced sub-filamentation (Gregori et al 1999(Gregori et al , 2000Banda-Barragán et al 2016). Since the density PDF is correlated with the magnetic field distribution in turbulent clouds (Federrath & Klessen 2012), we also expect the evolution of wind-swept solenoidal and compressive fractal cloud models to be different.…”

Section: Caveats and Future Workmentioning

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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“…Indeed, magnetic field are known to have non trivial effects on the dynamics of cold gas clouds travelling through the hot coronal medium (e.g. Grønnow et al 2017Grønnow et al , 2018.…”

Section: Discussionmentioning

confidence: 99%

The effect of rotation on the thermal instability of stratified galactic atmospheres – II. The formation of high-velocity clouds

Sormani

Sobacchi

2019

Monthly Notices of the Royal Astronomical Society

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Whether High Velocity Clouds (HVCs) can form by condensation of the hot (T ∼ 10 6 K) Galactic corona as a consequence of thermal instabilities has been controversial. Here we re-examine this problem and we suggest that rotation of the corona might be a missing key ingredient. We do this by studying the evolution of the models of rotating galactic coronae presented in Sormani et al. (2018) under the presence of cooling and thermal conduction. We combine a linear stability analysis with the results of local and global hydrodynamical simulations. We find that condensations are likely to occur in regions where the corona has substantial rotational support. Under reasonably general assumptions on the rotation profile of the corona, the locations where condensations are expected are in remarkable agreement with the observed location of the major non-magellanic HVCs complexes in our Galaxy (namely, at distances 15 kpc from the Sun and within 30 • from the disc plane). We conclude that HVCs can form by thermal instabilities provided that (i) the corona is rotating substantially in the inner (R 50 kpc) parts, as suggested by current observational data and predicted by cosmological simulations of galaxy formation; (ii) close to the disc the corona is well-represented by a nearly-equilibrium stratified rotating structure (as opposed to a fast cooling flow). Our results also suggest that a better understanding of the disc-halo interface, including supernova feedback, is critical to understand the origin of HVCs.

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Magnetized High Velocity Clouds in the Galactic Halo: A New Distance Constraint

Cited by 33 publications

References 66 publications

The Launching of Cold Clouds by Galaxy Outflows. III. The Influence of Magnetic Fields

The Launching of Cold Clouds by Galaxy Outflows. III. The Influence of Magnetic Fields

On the dynamics and survival of fractal clouds in galactic winds

The effect of rotation on the thermal instability of stratified galactic atmospheres – II. The formation of high-velocity clouds

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