Lecture: Manifestations and Physics of Galactic Winds and Outflows (1/2)

The lecture is held in two parts. 1st part on Wednesday, 2nd part on Thursday.

By registering you agree to be listed as participant here on the event page.

Outline:

1. Manifestations of Galactic Outflows

• emphasis on Milky Way, but the physics is applicable to all Galaxies at all redshifts
• observed features
  • bipolar outflow on 10-pc scale
  •  the Galactic center chimneys, radio an X-ray - large-scale synchrotron radio features
  • Fermi Bubbles
  • eRosita Bubbles

2. Sources of gas outflow from galaxies

• AGNs: jets versus winds
• tidal disruption events
• star formation, —> supernovae
• collective supernovae

3. The Galactic wind

• broad angular distribution relative to Galactic center
• entrained neutral gas clumps as best evidence
• fate of dense gas clumps: disintegration or growth
  • ablation
  • instabilities: Rayleigh-Taylor, Kelvin-Helmholtz
  • compression —> enhanced cooling, density growth

4. Determinants of the expansion rate of outflows

• initial ejection velocity, if any
• temperature (sound speed) —> adiabatic expansion
  • plasma cooling time versus expansion time
• gravitational deceleration
• shocks with ambient gas, mass loading

5. The Galactic Magnetic Field

• a collimator for the wind
  • versus collimation caused by Galactic density gradient
• magnetic pressure versus ram pressure versus gas pressure how strong does the field need to be?

6. Relativistic gas —> Cosmic Rays

• acceleration mechanisms
• diffusion
• role of magnetic fields
• anisotropy of diffusion coefficients
• synchrotron emission
• application to Fermi Bubbles

7. Interaction with the Galactic halo

• shocks
• sharp bubble edges: quasi-steady shock or surface moving in response to energy injection?
• what goes up must come down: the Galactic fountain
  • cooling instabilities