15-08 Formation and Evolution of Galaxies

• Does the tuning fork diagram, Hubble's galaxy types, tell us anything?
   
• Galaxies formed from merging of gas clouds?
  
  
  [The formation of galaxies; the so-called 'top-down' and 'bottom-up' scenarios.]
  
  
  [The building blocks of galaxies, containing young stars and gas]
   
• One possible way of forming spirals and ellipticals: When protogalaxies formed, star formation was triggered.
  stars form slowly --> spirals
  stars form quickly --> ellipticals
  
  
  [Star birth rate in elliptical and spiral galaxies]
  
   
• Looking back to the earlier universe:
  More spirals than now:
  in rich clusters at z = 0.4 (roughly 4 billion years look-back time), about 30% galaxies are spirals;
  in nearby ones only about 5%
   
  Does interaction produce ellipticals from spirals?
   
• Large scale structure : galaxies formed first, then structured? or ? why? Dark matter?