16-02 Shapes of Galaxies

  • a galaxy gallery




     
  • Hubble's tuning fork diagram


    'early type' (ellipticals) vs 'late type' (spirals and irregulars)
     
  • spiral galaxies
     
    normal spirals: Sa, Sb, Sc


    barred spirals: SBa, SBb, SBc


    note: closer to type a, a larger central bulge, more tightly wound spiral arms, less gas and dust
     
  • elliptical galaxies
     
    giant ellipticals
    [Two giant ellipticals near the central part of the Virgo cluster, 15 Mpc away; M84 and M86 span 5 to 7 arcmin.]

    dwarf ellipticals
    [Leo I, a dwarf elliptical of size 1 kpc, 180 kpc away]

    note: giant ellipticals are rare, while dwarf ellipticals are quite common.
     
  • irregular galaxies



    [The Large Magellanic Cloud (LMC), 49 kpc away, 19 kpc across; to the left is a huge HII region called Tarantula Nebula or 30 Doradus, which is about 5 million solar masses, 250pc large.]

    [The Small Magellanic Cloud (SMC), 61 kpc away, 8 kpc across; to the right is a galactic globular cluster, 47 Tucanae)

    Irregulars often have more gas and dust, with active star formation.
    Irr I (with hint of some organized structure), or --> Sd(SBd), Sm(SBm), Im; (LMC is an SBm; SMC is an Im; 'm' stands for Magellanic type)
    Irr II (totally disorganized), or --> Ir (Amorphous); (M82 is an Ir)
     
    [Subaru telescope and Chandra X-ray Observatory images of M82, an amorphous galaxy]

  • some properties of galaxies
    Elliptical Spiral Irregular
    Mass (solar mass) 105 - 1013 109 - 4 x 1011 108 - 3 x 1010
    Luminosity (solar luminosity) 3 x 105 - 1011 108 - 2 x 1010 107 - 109
    Diameter (kpc) 1 - 200 5 - 250 1 - 10
    Stellar populations Population II
    and old Population I    		 disk: young Population I
    central bulge and halo:
    Population II and old Population I    		 mostly Population I
    Percentage of observed galaxies 20% 77% 3%
    note: many dwarf ellipticals are too dim to observe. Properties of Galaxies