16-03 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]