17-01 Seyfert Galaxies and Radio Galaxies

  • Seyfert Galaxies
    (what should the spectrum of a galaxy look like?)
    1943, Carl Seyfert published his study of some spiral galaxies with peculiar nuclei.
    'peculiar' - bright, unresolved
    They have emission lines on top of a strong continuum in their spectra!

    [the Seyfert galaxy NGC 1566]

    [the Seyfert galaxy NGC 7742]

     
  • Seyfert I: broad emission lines (1000 km/sec ~ 10000 km/sec), luminous in UV, X-rays
  • Seyfert II: narrow emission lines ( ~ 500 km/sec), luminous in IR
     
    [the Seyfert I spectrum]

    [the Seyfert II spectrum]

     
  • the Seyferts may vary significantly within weeks
  • about 1% of all spiral galaxies is Seyfert galaxies
    (what could make a bright, varying, compact core of a Seyfert galaxy?)

  • Radio Galaxies

    [Cygnus A]

    The first discrete radio sources other than the Sun is Cygnus A.
    Walter Baade and Rudolph Minkowski found the optical counterpart of Cyg A.
    It is a peculiar (with emission lines) cD (supergiant elliptical with a diffuse envelope) galaxy.
    Its redshift is 0.056, corresponding to a recession velocity of 16,000 km/sec, a distance of 170h-1 Mpc.
     
    double-lobed radio sources

    [3C 388]

    typical sizes are 50 kpc ~ 5 Mpc
    the central galaxy is usually a giant elliptical, also with emission lines (NLRGs, BLRGs)
    (Seyferts are radio-quiet spirals; radio galaxies are ellipticals)

    [Centaurus A]

     
  • jets or beams?

    1. hot spots

    [an inner section of the M87 jet]

    2. superluminal motion (a movie of the M87 jet; see the next section for the cause of being superluminal.)
     
    3. power-law spectra (nonthermal, very probably from synchrotron radition) 

    [the synchrotron radiation spectrum]

     
  • jets and lobes

    the formation (ejection and collimation) of jets is still poorly understood

    one-sided jets
    [the M87 radio image]

    head-tail radio galaxies
    [NGC1265]