Atomic Collisions

• cross sections
• critical densities
• awesome example: C⁺ line [C II] 158 microns
  • in Orion
  • all sky map (Fixsen+ 1999)
  • in a model galaxy spectrum
  • galaxy images: NGC 7331 (HST optical), and fireworks galaxy
  • in a z~7 star-forming galaxy

Electron-Atom Collisions

Nebular Diagnostics

• examples:
  I Zwicky 18: optical image, spectrum
  • SN 1006: optical image, filament spectrum (Ghavamian+ 2002)
• temperature diagnostics
• density diagnostics