4. DISK GALAXIES

4.1 Surface Photometry

• Radial brightness profiles of bulges and disks:
  
  • Analytic fitting functions
    
• Disk parameter corrrelations
  
• Bulge-disk decomposition
  
• Vertical brightness pro files of disks:
  
  • Analytic fitting functions
    
• Thick disks
  
  

4.2 Bulge Dynamics

• Evidence that some “bulges” are really disks
  
• Revised bulge-to-total luminosity ratios as function of Hubble type
  
  

4.3 Vertical Structure of Thin Disks: Theory

• The isothermal sheet
  
  

4.4 Local Stability of Disks

• Jeans instability: velocity dispersion stabilizes small-scale perturbations
  
• Rotation stabilizes large-scale perturbations
  
• Complete stability: Toomre ’s Q parameter
  
• Observations: Q in the Galactic solar neighborhood
  
• Observations: Q in other galaxy disks
  
• Other disk heating mechanisms:
  
  • Lumps: the Spitzer-Schwarzschild mechanism
    
  • Scattering by bars and spiral structure
    
  • Heating by accreted satellites
    
    

4.5 Spiral Structure

• Observations of global spiral structure
  
• Epicyclic theory
  
• Kinematic spiral density waves
  
• Dynamical spiral density waves
  
• Swing amplification
  
• Observational consequences and tests
  
• Alternatives:
  
  • Self-propagating star formation and flocculent spirals
    
  • Tidal spirals
    
    

4.6 Bars

• Observed properties of SB galaxies: bars, rings, and lenses
  
• Formation and evolution of bars: n-body simulations
  
• Importance of bars: secular evolution
  
  • Orbits in barred potentials
    
  • Radial transport of gas; star formation
    
  • Stellar-dynamical secular evolution <= density redistribution, angular momentum transport
    
  • Formation or box-shaped bulges and lenses (?)
    
    

4.7 Kinematics of the Galactic Solar Neighborhood

• Standards of rest
  
• Effects of galactic rotation
  
  • Intuitive picture
    
  • Global formulae
    
  • Local approximations
    
• Random velocities in the solar neighborhood: velocity ellipsoid
  
• Asymmetric drift
  
  

4.8 Global Structure of the Galaxy

• The Hubble type of the Galaxy
  
• Galactic parameters
  
• Thin disk (Population I)
  
• Stellar halo (Population II)
  
• Thick disk (Intermediate Population II)
  
• Evidence that the Galaxy is barred
  
  

4.9 Warps in Galaxy Disks

• Observations (mostly HI)
  
• The problem: formation and maintenance of warps
  
• The solution: triaxial dark halos?