A systematic approach to studying the physics of cool clouds in the - - PowerPoint PPT Presentation

A systematic approach to studying the physics of cool clouds in the hot winds of galaxy halos

Ian Remming & Cameron Liang University of Chicago

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MHD+cooling O VI abundance Hot Wind

2 Image credit: HST

Why is the CGM multiphase?

Perform hi-res simulations (Δ < 1 pc) of … warm turbulent clouds

~~ moving through ~~

hot winds

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• 1. What role does radiative cooling/heating play?
• 2. How efficient is thermal conduction?
• 3. Are magnetic fields needed?

What are the physical processes shaping the CGM on small scales?

Image credit: HST

Why is the CGM multiphase?

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Low-ions as slow moving, dense cooling fragments. Is there characteristic size? High-ions in the stripped outer layers that forms the fast moving, turbulent wake.

Gnedin & Hollon 2012, Haardt & Madau 2012, McCourt+ 2017,

Radiative Cooling/Heating only

Schneider & Robertson 2017 , Scannapieco & Brüggen 2015

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The cloud cools, increasing the abundance of low-ions. Thermal conduction turns low-ion gas to high-ions. The cloud fully evaporates by < 7 Myr.

Spitzer 1962, Cowie & McKee 1977, Armillotta+ 2016, Armillotta+ 2017

Cooling/heating + isotropic thermal conduction

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Radiative Cooling/Heating

(Gnedin & Hollon 2012, Haardt & Madau 2012)

+

Anisotropic Thermal Conduction

(Meyer, Balsara & Aslam 2012, 2014)

… β-1 ≡ B2/(8 π P) = 1.0 … B ~ 2.6 μG

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High-ion gas form warm wake threaded by field lines.

Meyer, Balsara & Aslam 2012, 2014, Orlando+ 2008, McCourt+ 2015

Low-ion gas insulated by magnetic field.

Cooling/heating + anisotropic thermal conduction

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The B-field moves with the gas, tangles, and wraps around cold filaments. Protects cold gas from the wind. The stronger B-field contains the cooling gas in one long feature. The B-field insulates the cold gas from the hot environment. Cloud core cools and shatters. Wind compresses and breaks apart fragments.

β-1 = 0, cooling only β-1 =0.1, Weak Field and cooling β-1 =1.0, strong field and cooling β-1 =1.0, cooling, anisotropic conduction

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The B-field moves with the gas, tangles, and wraps around cold filaments. Protects cold gas from the wind. The stronger B-field contains the cooling gas in one long feature. The B-field insulates the cold gas from the hot environment. Cloud core cools and shatters. Wind compresses and breaks apart fragments.

β-1 = 0, cooling only β-1 =0.1, Weak Field and cooling β-1 =1.0, strong field and cooling β-1 =1.0, cooling, anisotropic conduction

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Magnetic field insulation

β-1 = 0.1 β-1 = 1.0 β-1 = 1.0 + conduction Around cold, dense features, the magnetic field lines are compressed. The B-field protects the gas from shear instabilities and conduction.

−4 −3 −2 −1 log nH [cm−3] 4 5 6 7 log T [K] 1.0 2.0 2.8 log β−1

51 pc 51 pc

Weak initial field Strong initial field

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• 1. What role does radiative cooling/heating play?
• 2. How efficient is thermal conduction?
• 3. Are magnetic fields needed?

◼ Protecting from shear instabilities

and conduction.

−4 −3 −2 −1 log nH [cm−3] 4 5 6 7 log T [K] 1.0 2.0 2.8 log β−1

◼ Field lines drape around pc-scale

dense features.

◼ The warm cloud shatters.

(see McCourt’s talk later today)

◼ The cloud fully evaporates on a short timescale < 7 Myr. ◼ Enhancing the local field strength,

even for initially weak fields.

Conclusion