15-03 Distance to Galaxies

  • Distance! distance! distance!
    parallax, spectroscopic parallax, main-sequence fitting, and the moving-cluster method
     
  • Distance indicators
     
  • Using Cepheids,
    with ground-based telescopes, up to about 6 Mpc
    with HST, up to about 40 Mpc
    (check, Mv ~ -3, @ 6 Mpc, mv ~ 26; @ 40 Mpc, mv ~ 30)


    [The absolute magnitude - period relation for Cepheids: Type I, Type II Cepheids, RR Lyrae]

  • Other distance indicators:
    Red supergiants, average absolute magnitude ~ -9     (4 times farther than using Cepheids with Mv ~ -6)
    Large globular clusters, average absolute magnitude ~ -10
    Large H-II regions, average absolute magnitude ~ -12
    *** Maxima of supernovae (Type Ia ~ -19)


    [The light curves of supernovae]

    Large spiral galaxies, average absolute magnitude ~ -21
     
  • Tully-Fisher relation
    The measured width of 21cm lines indicates the rotation of target spiral galaxies.


    [The rotation curves of spiral galaxies]



    [The Tully-Fisher relation]

  • Improvements of calibration


    [The distance ladder]