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 MHD+cooling Hot Wind O VI abundance 1

Why is the CGM multiphase? Image credit: HST Perform hi-res simulations ( Δ < 1 pc) of … warm turbulent clouds ~~ moving through ~~ hot winds 2

Why is the CGM multiphase? Image credit: HST 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? 3

Radiative Cooling/Heating only 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, Schneider & Robertson 2017 , Scannapieco & Brüggen 2015 4

Cooling/heating + isotropic thermal conduction 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 5

Radiative Cooling/Heating (Gnedin & Hollon 2012, Haardt & Madau 2012) + Anisotropic Thermal Conduction (Meyer, Balsara & Aslam 2012, 2014) … β -1 ≡ B 2 /(8 π P) = 1.0 … B ~ 2.6 μ G 6

Cooling/heating + anisotropic thermal conduction Low-ion gas insulated by magnetic field. High-ion gas form warm wake threaded by field lines. Meyer, Balsara & Aslam 2012, 2014 , Orlando+ 2008, McCourt+ 2015 7

β -1 = 0, cooling only β -1 =0.1, Weak Field and cooling The B-field moves with the gas, tangles, and Cloud core cools and shatters. Wind wraps around cold filaments. Protects cold gas compresses and breaks apart fragments. from the wind. β -1 =1.0, strong field and cooling β -1 =1.0, cooling, anisotropic conduction The stronger B-field contains the The B-field insulates the cold gas from the hot cooling gas in one long feature. environment. 8

β -1 = 0, cooling only β -1 =0.1, Weak Field and cooling The B-field moves with the gas, tangles, and Cloud core cools and shatters. Wind wraps around cold filaments. Protects cold gas compresses and breaks apart fragments. from the wind. β -1 =1.0, strong field and cooling β -1 =1.0, cooling, anisotropic conduction The stronger B-field contains the The B-field insulates the cold gas from the hot cooling gas in one long feature. environment. 9

Magnetic field insulation 51 pc β -1 = 0.1 51 pc Weak initial field β -1 = 1.0 Strong initial field β -1 = 1.0 + conduction Around cold, dense features, the magnetic field lines are compressed. The B-field protects the − 4 − 3 − 2 − 1 4 5 6 7 1 . 0 2 . 0 2 . 8 log n H [cm − 3 ] log T [K] log β − 1 gas from shear instabilities and conduction. 10

Conclusion 1. What role does radiative cooling/heating play? ◼ The warm cloud shatters . (see McCourt’s talk later today) 2. How efficient is thermal conduction ? ◼ The cloud fully evaporates on a short timescale < 7 Myr. 3. Are magnetic fields needed? ◼ Field lines drape around pc-scale dense features. ◼ Enhancing the local field strength, even for initially weak fields. ◼ Protecting from shear instabilities and conduction. − 4 − 3 − 2 − 1 4 5 6 7 1 . 0 2 . 0 2 . 8 11 log n H [cm − 3 ] log T [K] log β − 1